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FLEX(1)			   OpenBSD Reference Manual		       FLEX(1)

NAME
     flex - fast lexical analyzer generator

SYNOPSIS
     flex [-78BbcdFfhIiLlnpsTtVvw+?] [-C[aeFfmr]] [--help] [--version]
	  [-ooutput] [-Pprefix] [-Sskeleton] [file ...]

DESCRIPTION
     flex is a tool for generating scanners: programs which recognize lexical
     patterns in text.	flex reads the given input files, or its standard
     input if no file names are given, for a description of a scanner to
     generate.	The description is in the form of pairs of regular expressions
     and C code, called rules.	flex generates as output a C source file,
     lex.yy.c, which defines a routine yylex().	 This file is compiled and
     linked with the -lfl library to produce an executable.  When the
     executable is run, it analyzes its input for occurrences of the regular
     expressions.  Whenever it finds one, it executes the corresponding C
     code.

     The manual includes both tutorial and reference sections:

     Some Simple Examples

     Format of the Input File

     Patterns
     The extended regular expressions used by flex.

     How the Input is Matched
     The rules for determining what has been matched.

     Actions
     How to specify what to do when a pattern is matched.

     The Generated Scanner
     Details regarding the scanner that flex produces; how to control the
     input source.

     Start Conditions
     Introducing context into scanners, and managing "mini-scanners".

     Multiple Input Buffers
     How to manipulate multiple input sources; how to scan from strings
     instead of files.

     End-of-File Rules
     Special rules for matching the end of the input.

     Miscellaneous Macros
     A summary of macros available to the actions.

     Values Available to the User
     A summary of values available to the actions.

     Interfacing with Yacc
     Connecting flex scanners together with yacc(1) parsers.

     Options
     flex command-line options, and the ``%option'' directive.

     Performance Considerations
     How to make scanners go as fast as possible.

     Generating C++ Scanners
     The (experimental) facility for generating C++ scanner classes.

     Incompatibilities with Lex and POSIX
     How flex differs from AT&T lex and the POSIX lex standard.

     Files
     Files used by flex.

     Diagnostics
     Those error messages produced by flex (or scanners it generates) whose
     meanings might not be apparent.

     See Also
     Other documentation, related tools.

     Authors
     Includes contact information.

     Bugs
     Known problems with flex.

SOME SIMPLE EXAMPLES
     First some simple examples to get the flavor of how one uses flex.	 The
     following flex input specifies a scanner which whenever it encounters the
     string "username" will replace it with the user's login name:

	   %%
	   username    printf("%s", getlogin());

     By default, any text not matched by a flex scanner is copied to the
     output, so the net effect of this scanner is to copy its input file to
     its output with each occurrence of "username" expanded.  In this input,
     there is just one rule.  "username" is the pattern and the "printf" is
     the action.  The "%%" marks the beginning of the rules.

     Here's another simple example:

	   %{
	   int num_lines = 0, num_chars = 0;
	   %}

	   %%
	   \n	   ++num_lines; ++num_chars;
	   .	   ++num_chars;

	   %%
	   main()
	   {
		   yylex();
		   printf("# of lines = %d, # of chars = %d\n",
		       num_lines, num_chars);
	   }

     This scanner counts the number of characters and the number of lines in
     its input (it produces no output other than the final report on the
     counts).  The first line declares two globals, "num_lines" and
     "num_chars", which are accessible both inside yylex() and in the main()
     routine declared after the second "%%".  There are two rules, one which
     matches a newline ("\n") and increments both the line count and the
     character count, and one which matches any character other than a newline
     (indicated by the "." regular expression).

     A somewhat more complicated example:

	   /* scanner for a toy Pascal-like language */

	   %{
	   /* need this for the call to atof() below */
	   #include <math.h>
	   %}

	   DIGIT    [0-9]
	   ID	    [a-z][a-z0-9]*

	   %%

	   {DIGIT}+ {
		   printf("An integer: %s (%d)\n", yytext,
		       atoi(yytext));
	   }

	   {DIGIT}+"."{DIGIT}* {
		   printf("A float: %s (%g)\n", yytext,
		       atof(yytext));
	   }

	   if|then|begin|end|procedure|function {
		   printf("A keyword: %s\n", yytext);
	   }

	   {ID}	   printf("An identifier: %s\n", yytext);

	   "+"|"-"|"*"|"/"   printf("An operator: %s\n", yytext);

	   "{"[^}\n]*"}"     /* eat up one-line comments */

	   [ \t\n]+	     /* eat up whitespace */

	   .	   printf("Unrecognized character: %s\n", yytext);

	   %%

	   main(int argc, char *argv[])
	   {
		   ++argv; --argc;  /* skip over program name */
		   if (argc > 0)
			   yyin = fopen(argv[0], "r");
		   else
			   yyin = stdin;

		   yylex();
	   }

     This is the beginnings of a simple scanner for a language like Pascal.
     It identifies different types of tokens and reports on what it has seen.

     The details of this example will be explained in the following sections.

FORMAT OF THE INPUT FILE
     The flex input file consists of three sections, separated by a line with
     just "%%" in it:

	   definitions
	   %%
	   rules
	   %%
	   user code

     The definitions section contains declarations of simple name definitions
     to simplify the scanner specification, and declarations of start
     conditions, which are explained in a later section.

     Name definitions have the form:

	   name definition

     The "name" is a word beginning with a letter or an underscore (`_')
     followed by zero or more letters, digits, `_', or `-' (dash).  The
     definition is taken to begin at the first non-whitespace character
     following the name and continuing to the end of the line.	The definition
     can subsequently be referred to using "{name}", which will expand to
     "(definition)".  For example:

	   DIGIT    [0-9]
	   ID	    [a-z][a-z0-9]*

     This defines "DIGIT" to be a regular expression which matches a single
     digit, and "ID" to be a regular expression which matches a letter
     followed by zero-or-more letters-or-digits.  A subsequent reference to

	   {DIGIT}+"."{DIGIT}*

     is identical to

	   ([0-9])+"."([0-9])*

     and matches one-or-more digits followed by a `.' followed by zero-or-more
     digits.

     The rules section of the flex input contains a series of rules of the
     form:

	   pattern   action

     The pattern must be unindented and the action must begin on the same
     line.

     See below for a further description of patterns and actions.

     Finally, the user code section is simply copied to lex.yy.c verbatim.  It
     is used for companion routines which call or are called by the scanner.
     The presence of this section is optional; if it is missing, the second
     "%%" in the input file may be skipped too.

     In the definitions and rules sections, any indented text or text enclosed
     in `%{' and `%}' is copied verbatim to the output (with the %{}'s
     removed).	The %{}'s must appear unindented on lines by themselves.

     In the rules section, any indented or %{} text appearing before the first
     rule may be used to declare variables which are local to the scanning
     routine and (after the declarations) code which is to be executed
     whenever the scanning routine is entered.	Other indented or %{} text in
     the rule section is still copied to the output, but its meaning is not
     well-defined and it may well cause compile-time errors (this feature is
     present for POSIX compliance; see below for other such features).

     In the definitions section (but not in the rules section), an unindented
     comment (i.e., a line beginning with "/*") is also copied verbatim to the
     output up to the next "*/".

PATTERNS
     The patterns in the input are written using an extended set of regular
     expressions.  These are:

     x	       Match the character `x'.

     .	       Any character (byte) except newline.

     [xyz]     A "character class"; in this case, the pattern matches either
	       an `x', a `y', or a `z'.

     [abj-oZ]  A "character class" with a range in it; matches an `a', a `b',
	       any letter from `j' through `o', or a `Z'.

     [^A-Z]    A "negated character class", i.e., any character but those in
	       the class.  In this case, any character EXCEPT an uppercase
	       letter.

     [^A-Z\n]  Any character EXCEPT an uppercase letter or a newline.

     r*	       Zero or more r's, where `r' is any regular expression.

     r+	       One or more r's.

     r?	       Zero or one r's (that is, "an optional r").

     r{2,5}    Anywhere from two to five r's.

     r{2,}     Two or more r's.

     r{4}      Exactly 4 r's.

     {name}    The expansion of the "name" definition (see above).

     "[xyz]\"foo"
	       The literal string: [xyz]"foo.

     \X	       If `X' is an `a', `b', `f', `n', `r', `t', or `v', then the
	       ANSI-C interpretation of `\X'.  Otherwise, a literal `X' (used
	       to escape operators such as `*').

     \0	       A NUL character (ASCII code 0).

     \123      The character with octal value 123.

     \x2a      The character with hexadecimal value 2a.

     (r)       Match an `r'; parentheses are used to override precedence (see
	       below).

     rs	       The regular expression `r' followed by the regular expression
	       `s'; called "concatenation".

     r|s       Either an `r' or an `s'.

     r/s       An `r', but only if it is followed by an `s'.  The text matched
	       by `s' is included when determining whether this rule is the
	       "longest match", but is then returned to the input before the
	       action is executed.  So the action only sees the text matched
	       by `r'.	This type of pattern is called "trailing context".
	       (There are some combinations of r/s that flex cannot match
	       correctly; see notes in the BUGS section below regarding
	       "dangerous trailing context".)

     ^r	       An `r', but only at the beginning of a line (i.e., just
	       starting to scan, or right after a newline has been scanned).

     r$	       An `r', but only at the end of a line (i.e., just before a
	       newline).  Equivalent to "r/\n".

	       Note that flex's notion of "newline" is exactly whatever the C
	       compiler used to compile flex interprets `\n' as.

     <s>r      An `r', but only in start condition `s' (see below for
	       discussion of start conditions).

     <s1,s2,s3>r
	       The same, but in any of start conditions s1, s2, or s3.

     <*>r      An `r' in any start condition, even an exclusive one.

     <<EOF>>   An end-of-file.

     <s1,s2><<EOF>>
	       An end-of-file when in start condition s1 or s2.

     Note that inside of a character class, all regular expression operators
     lose their special meaning except escape (`\') and the character class
     operators, `-', `]', and, at the beginning of the class, `^'.

     The regular expressions listed above are grouped according to precedence,
     from highest precedence at the top to lowest at the bottom.  Those
     grouped together have equal precedence.  For example,

	   foo|bar*

     is the same as

	   (foo)|(ba(r*))

     since the `*' operator has higher precedence than concatenation, and
     concatenation higher than alternation (`|').  This pattern therefore
     matches either the string "foo" or the string "ba" followed by zero-or-
     more r's.	To match "foo" or zero-or-more "bar"'s, use:

	   foo|(bar)*

     and to match zero-or-more "foo"'s-or-"bar"'s:

	   (foo|bar)*

     In addition to characters and ranges of characters, character classes can
     also contain character class expressions.	These are expressions enclosed
     inside `[:' and `:]' delimiters (which themselves must appear between the
     `[' and `]' of the character class; other elements may occur inside the
     character class, too).  The valid expressions are:

	   [:alnum:] [:alpha:] [:blank:]
	   [:cntrl:] [:digit:] [:graph:]
	   [:lower:] [:print:] [:punct:]
	   [:space:] [:upper:] [:xdigit:]

     These expressions all designate a set of characters equivalent to the
     corresponding standard C isXXX() function.	 For example, [:alnum:]
     designates those characters for which isalnum(3) returns true - i.e., any
     alphabetic or numeric.  Some systems don't provide isblank(3), so flex
     defines [:blank:] as a blank or a tab.

     For example, the following character classes are all equivalent:

	   [[:alnum:]]
	   [[:alpha:][:digit:]]
	   [[:alpha:]0-9]
	   [a-zA-Z0-9]

     If the scanner is case-insensitive (the -i flag), then [:upper:] and
     [:lower:] are equivalent to [:alpha:].

     Some notes on patterns:

     -	 A negated character class such as the example "[^A-Z]" above will
	 match a newline unless "\n" (or an equivalent escape sequence) is one
	 of the characters explicitly present in the negated character class
	 (e.g., "[^A-Z\n]").  This is unlike how many other regular expression
	 tools treat negated character classes, but unfortunately the
	 inconsistency is historically entrenched.  Matching newlines means
	 that a pattern like "[^"]*" can match the entire input unless there's
	 another quote in the input.

     -	 A rule can have at most one instance of trailing context (the `/'
	 operator or the `$' operator).	 The start condition, `^', and
	 "<<EOF>>" patterns can only occur at the beginning of a pattern, and,
	 as well as with `/' and `$', cannot be grouped inside parentheses.  A
	 `^' which does not occur at the beginning of a rule or a `$' which
	 does not occur at the end of a rule loses its special properties and
	 is treated as a normal character.

     -	 The following are illegal:

	       foo/bar$
	       <sc1>foo<sc2>bar

	 Note that the first of these, can be written "foo/bar\n".

     -	 The following will result in `$' or `^' being treated as a normal
	 character:

	       foo|(bar$)
	       foo|^bar

	 If what's wanted is a "foo" or a bar-followed-by-a-newline, the
	 following could be used (the special `|' action is explained below):

	       foo	|
	       bar$	/* action goes here */

	 A similar trick will work for matching a foo or a bar-at-the-
	 beginning-of-a-line.

HOW THE INPUT IS MATCHED
     When the generated scanner is run, it analyzes its input looking for
     strings which match any of its patterns.  If it finds more than one
     match, it takes the one matching the most text (for trailing context
     rules, this includes the length of the trailing part, even though it will
     then be returned to the input).  If it finds two or more matches of the
     same length, the rule listed first in the flex input file is chosen.

     Once the match is determined, the text corresponding to the match (called
     the token) is made available in the global character pointer yytext, and
     its length in the global integer yyleng.  The action corresponding to the
     matched pattern is then executed (a more detailed description of actions
     follows), and then the remaining input is scanned for another match.

     If no match is found, then the default rule is executed: the next
     character in the input is considered matched and copied to the standard
     output.  Thus, the simplest legal flex input is:

	   %%

     which generates a scanner that simply copies its input (one character at
     a time) to its output.

     Note that yytext can be defined in two different ways: either as a
     character pointer or as a character array.	 Which definition flex uses
     can be controlled by including one of the special directives ``%pointer''
     or ``%array'' in the first (definitions) section of flex input.  The
     default is ``%pointer'', unless the -l lex compatibility option is used,
     in which case yytext will be an array.  The advantage of using
     ``%pointer'' is substantially faster scanning and no buffer overflow when
     matching very large tokens (unless not enough dynamic memory is
     available).  The disadvantage is that actions are restricted in how they
     can modify yytext (see the next section), and calls to the unput()
     function destroy the present contents of yytext, which can be a
     considerable porting headache when moving between different lex versions.

     The advantage of ``%array'' is that yytext can be modified as much as
     wanted, and calls to unput() do not destroy yytext (see below).
     Furthermore, existing lex programs sometimes access yytext externally
     using declarations of the form:

	   extern char yytext[];

     This definition is erroneous when used with ``%pointer'', but correct for
     ``%array''.

     ``%array'' defines yytext to be an array of YYLMAX characters, which
     defaults to a fairly large value.	The size can be changed by simply
     #define'ing YYLMAX to a different value in the first section of flex
     input.  As mentioned above, with ``%pointer'' yytext grows dynamically to
     accommodate large tokens.	While this means a ``%pointer'' scanner can
     accommodate very large tokens (such as matching entire blocks of
     comments), bear in mind that each time the scanner must resize yytext it
     also must rescan the entire token from the beginning, so matching such
     tokens can prove slow.  yytext presently does not dynamically grow if a
     call to unput() results in too much text being pushed back; instead, a
     run-time error results.

     Also note that ``%array'' cannot be used with C++ scanner classes (the
     c++ option; see below).

ACTIONS
     Each pattern in a rule has a corresponding action, which can be any
     arbitrary C statement.  The pattern ends at the first non-escaped
     whitespace character; the remainder of the line is its action.  If the
     action is empty, then when the pattern is matched the input token is
     simply discarded.	For example, here is the specification for a program
     which deletes all occurrences of "zap me" from its input:

	   %%
	   "zap me"

     (It will copy all other characters in the input to the output since they
     will be matched by the default rule.)

     Here is a program which compresses multiple blanks and tabs down to a
     single blank, and throws away whitespace found at the end of a line:

	   %%
	   [ \t]+	 putchar(' ');
	   [ \t]+$	 /* ignore this token */

     If the action contains a `{', then the action spans till the balancing
     `}' is found, and the action may cross multiple lines.  flex knows about
     C strings and comments and won't be fooled by braces found within them,
     but also allows actions to begin with `%{' and will consider the action
     to be all the text up to the next `%}' (regardless of ordinary braces
     inside the action).

     An action consisting solely of a vertical bar (`|') means "same as the
     action for the next rule".	 See below for an illustration.

     Actions can include arbitrary C code, including return statements to
     return a value to whatever routine called yylex().	 Each time yylex() is
     called, it continues processing tokens from where it last left off until
     it either reaches the end of the file or executes a return.

     Actions are free to modify yytext except for lengthening it (adding
     characters to its end - these will overwrite later characters in the
     input stream).  This, however, does not apply when using ``%array'' (see
     above); in that case, yytext may be freely modified in any way.

     Actions are free to modify yyleng except they should not do so if the
     action also includes use of yymore() (see below).

     There are a number of special directives which can be included within an
     action:

     ECHO    Copies yytext to the scanner's output.

     BEGIN   Followed by the name of a start condition, places the scanner in
	     the corresponding start condition (see below).

     REJECT  Directs the scanner to proceed on to the "second best" rule which
	     matched the input (or a prefix of the input).  The rule is chosen
	     as described above in HOW THE INPUT IS MATCHED, and yytext and
	     yyleng set up appropriately.  It may either be one which matched
	     as much text as the originally chosen rule but came later in the
	     flex input file, or one which matched less text.  For example,
	     the following will both count the words in the input and call the
	     routine special() whenever "frob" is seen:

		   int word_count = 0;
		   %%

		   frob	       special(); REJECT;
		   [^ \t\n]+   ++word_count;

	     Without the REJECT, any "frob"'s in the input would not be
	     counted as words, since the scanner normally executes only one
	     action per token.	Multiple REJECT's are allowed, each one
	     finding the next best choice to the currently active rule.	 For
	     example, when the following scanner scans the token "abcd", it
	     will write "abcdabcaba" to the output:

		   %%
		   a	    |
		   ab	    |
		   abc	    |
		   abcd	    ECHO; REJECT;
		   .|\n	    /* eat up any unmatched character */

	     (The first three rules share the fourth's action since they use
	     the special `|' action.)  REJECT is a particularly expensive
	     feature in terms of scanner performance; if it is used in any of
	     the scanner's actions it will slow down all of the scanner's
	     matching.	Furthermore, REJECT cannot be used with the -Cf or -CF
	     options (see below).

	     Note also that unlike the other special actions, REJECT is a
	     branch; code immediately following it in the action will not be
	     executed.

     yymore()
	     Tells the scanner that the next time it matches a rule, the
	     corresponding token should be appended onto the current value of
	     yytext rather than replacing it.  For example, given the input
	     "mega-kludge" the following will write "mega-mega-kludge" to the
	     output:

		   %%
		   mega-    ECHO; yymore();
		   kludge   ECHO;

	     First "mega-" is matched and echoed to the output.	 Then "kludge"
	     is matched, but the previous "mega-" is still hanging around at
	     the beginning of yytext so the ECHO for the "kludge" rule will
	     actually write "mega-kludge".

	     Two notes regarding use of yymore(): First, yymore() depends on
	     the value of yyleng correctly reflecting the size of the current
	     token, so yyleng must not be modified when using yymore().
	     Second, the presence of yymore() in the scanner's action entails
	     a minor performance penalty in the scanner's matching speed.

     yyless(n)
	     Returns all but the first n characters of the current token back
	     to the input stream, where they will be rescanned when the
	     scanner looks for the next match.	yytext and yyleng are adjusted
	     appropriately (e.g., yyleng will now be equal to n).  For
	     example, on the input "foobar" the following will write out
	     "foobarbar":

		   %%
		   foobar    ECHO; yyless(3);
		   [a-z]+    ECHO;

	     An argument of 0 to yyless will cause the entire current input
	     string to be scanned again.  Unless how the scanner will
	     subsequently process its input has been changed (using BEGIN, for
	     example), this will result in an endless loop.

	     Note that yyless is a macro and can only be used in the flex
	     input file, not from other source files.

     unput(c)
	     Puts the character c back into the input stream.  It will be the
	     next character scanned.  The following action will take the
	     current token and cause it to be rescanned enclosed in
	     parentheses.

		   {
			   int i;
			   char *yycopy;

			   /* Copy yytext because unput() trashes yytext */
			   if ((yycopy = strdup(yytext)) == NULL)
				   err(1, NULL);
			   unput(')');
			   for (i = yyleng - 1; i >= 0; --i)
				   unput(yycopy[i]);
			   unput('(');
			   free(yycopy);
		   }

	     Note that since each unput() puts the given character back at the
	     beginning of the input stream, pushing back strings must be done
	     back-to-front.

	     An important potential problem when using unput() is that if
	     using ``%pointer'' (the default), a call to unput() destroys the
	     contents of yytext, starting with its rightmost character and
	     devouring one character to the left with each call.  If the value
	     of yytext should be preserved after a call to unput() (as in the
	     above example), it must either first be copied elsewhere, or the
	     scanner must be built using ``%array'' instead (see HOW THE INPUT
	     IS MATCHED).

	     Finally, note that EOF cannot be put back to attempt to mark the
	     input stream with an end-of-file.

     input()
	     Reads the next character from the input stream.  For example, the
	     following is one way to eat up C comments:

		   %%
		   "/*" {
			   int c;

			   for (;;) {
				   while ((c = input()) != '*' && c != EOF)
					   ; /* eat up text of comment */

				   if (c == '*') {
					   while ((c = input()) == '*')
						   ;
					   if (c == '/')
						   break; /* found the end */
				   }

				   if (c == EOF) {
					   errx(1, "EOF in comment");
					   break;
				   }
			   }
		   }

	     (Note that if the scanner is compiled using C++, then input() is
	     instead referred to as yyinput(), in order to avoid a name clash
	     with the C++ stream by the name of input.)

     YY_FLUSH_BUFFER
	     Flushes the scanner's internal buffer so that the next time the
	     scanner attempts to match a token, it will first refill the
	     buffer using YY_INPUT (see THE GENERATED SCANNER, below).	This
	     action is a special case of the more general yy_flush_buffer()
	     function, described below in the section MULTIPLE INPUT BUFFERS.

     yyterminate()
	     Can be used in lieu of a return statement in an action.  It
	     terminates the scanner and returns a 0 to the scanner's caller,
	     indicating "all done".  By default, yyterminate() is also called
	     when an end-of-file is encountered.  It is a macro and may be
	     redefined.

THE GENERATED SCANNER
     The output of flex is the file lex.yy.c, which contains the scanning
     routine yylex(), a number of tables used by it for matching tokens, and a
     number of auxiliary routines and macros.  By default, yylex() is declared
     as follows:

	   int yylex()
	   {
	       ... various definitions and the actions in here ...
	   }

     (If the environment supports function prototypes, then it will be "int
     yylex(void)".)  This definition may be changed by defining the YY_DECL
     macro.  For example:

	   #define YY_DECL float lexscan(a, b) float a, b;

     would give the scanning routine the name lexscan, returning a float, and
     taking two floats as arguments.  Note that if arguments are given to the
     scanning routine using a K&R-style/non-prototyped function declaration,
     the definition must be terminated with a semi-colon (`;').

     Whenever yylex() is called, it scans tokens from the global input file
     yyin (which defaults to stdin).  It continues until it either reaches an
     end-of-file (at which point it returns the value 0) or one of its actions
     executes a return statement.

     If the scanner reaches an end-of-file, subsequent calls are undefined
     unless either yyin is pointed at a new input file (in which case scanning
     continues from that file), or yyrestart() is called.  yyrestart() takes
     one argument, a FILE * pointer (which can be nil, if YY_INPUT has been
     set up to scan from a source other than yyin), and initializes yyin for
     scanning from that file.  Essentially there is no difference between just
     assigning yyin to a new input file or using yyrestart() to do so; the
     latter is available for compatibility with previous versions of flex, and
     because it can be used to switch input files in the middle of scanning.
     It can also be used to throw away the current input buffer, by calling it
     with an argument of yyin; but better is to use YY_FLUSH_BUFFER (see
     above).  Note that yyrestart() does not reset the start condition to
     INITIAL (see START CONDITIONS, below).

     If yylex() stops scanning due to executing a return statement in one of
     the actions, the scanner may then be called again and it will resume
     scanning where it left off.

     By default (and for purposes of efficiency), the scanner uses block-reads
     rather than simple getc(3) calls to read characters from yyin.  The
     nature of how it gets its input can be controlled by defining the
     YY_INPUT macro.  YY_INPUT's calling sequence is
     "YY_INPUT(buf,result,max_size)".  Its action is to place up to max_size
     characters in the character array buf and return in the integer variable
     result either the number of characters read or the constant YY_NULL (0 on
     UNIX systems) to indicate EOF.  The default YY_INPUT reads from the
     global file-pointer "yyin".

     A sample definition of YY_INPUT (in the definitions section of the input
     file):

	   %{
	   #define YY_INPUT(buf,result,max_size) \
	   { \
		   int c = getchar(); \
		   result = (c == EOF) ? YY_NULL : (buf[0] = c, 1); \
	   }
	   %}

     This definition will change the input processing to occur one character
     at a time.

     When the scanner receives an end-of-file indication from YY_INPUT, it
     then checks the yywrap() function.	 If yywrap() returns false (zero),
     then it is assumed that the function has gone ahead and set up yyin to
     point to another input file, and scanning continues.  If it returns true
     (non-zero), then the scanner terminates, returning 0 to its caller.  Note
     that in either case, the start condition remains unchanged; it does not
     revert to INITIAL.

     If you do not supply your own version of yywrap(), then you must either
     use ``%option noyywrap'' (in which case the scanner behaves as though
     yywrap() returned 1), or you must link with -lfl to obtain the default
     version of the routine, which always returns 1.

     Three routines are available for scanning from in-memory buffers rather
     than files: yy_scan_string(), yy_scan_bytes(), and yy_scan_buffer().  See
     the discussion of them below in the section MULTIPLE INPUT BUFFERS.

     The scanner writes its ECHO output to the yyout global (default, stdout),
     which may be redefined by the user simply by assigning it to some other
     FILE pointer.

START CONDITIONS
     flex provides a mechanism for conditionally activating rules.  Any rule
     whose pattern is prefixed with "<sc>" will only be active when the
     scanner is in the start condition named "sc".  For example,

	   <STRING>[^"]* { /* eat up the string body ... */
		   ...
	   }

     will be active only when the scanner is in the "STRING" start condition,
     and

	   <INITIAL,STRING,QUOTE>\. { /* handle an escape ... */
		   ...
	   }

     will be active only when the current start condition is either "INITIAL",
     "STRING", or "QUOTE".

     Start conditions are declared in the definitions (first) section of the
     input using unindented lines beginning with either `%s' or `%x' followed
     by a list of names.  The former declares inclusive start conditions, the
     latter exclusive start conditions.	 A start condition is activated using
     the BEGIN action.	Until the next BEGIN action is executed, rules with
     the given start condition will be active and rules with other start
     conditions will be inactive.  If the start condition is inclusive, then
     rules with no start conditions at all will also be active.	 If it is
     exclusive, then only rules qualified with the start condition will be
     active.  A set of rules contingent on the same exclusive start condition
     describe a scanner which is independent of any of the other rules in the
     flex input.  Because of this, exclusive start conditions make it easy to
     specify "mini-scanners" which scan portions of the input that are
     syntactically different from the rest (e.g., comments).

     If the distinction between inclusive and exclusive start conditions is
     still a little vague, here's a simple example illustrating the connection
     between the two.  The set of rules:

	   %s example
	   %%

	   <example>foo	  do_something();

	   bar		  something_else();

     is equivalent to

	   %x example
	   %%

	   <example>foo	  do_something();

	   <INITIAL,example>bar	   something_else();

     Without the <INITIAL,example> qualifier, the ``bar'' pattern in the
     second example wouldn't be active (i.e., couldn't match) when in start
     condition ``example''.  If we just used <example> to qualify ``bar'',
     though, then it would only be active in ``example'' and not in INITIAL,
     while in the first example it's active in both, because in the first
     example the ``example'' start condition is an inclusive (`%s') start
     condition.

     Also note that the special start-condition specifier `<*>' matches every
     start condition.  Thus, the above example could also have been written:

	   %x example
	   %%

	   <example>foo	  do_something();

	   <*>bar	  something_else();

     The default rule (to ECHO any unmatched character) remains active in
     start conditions.	It is equivalent to:

	   <*>.|\n     ECHO;

     ``BEGIN(0)'' returns to the original state where only the rules with no
     start conditions are active.  This state can also be referred to as the
     start-condition INITIAL, so ``BEGIN(INITIAL)'' is equivalent to
     ``BEGIN(0)''.  (The parentheses around the start condition name are not
     required but are considered good style.)

     BEGIN actions can also be given as indented code at the beginning of the
     rules section.  For example, the following will cause the scanner to
     enter the "SPECIAL" start condition whenever yylex() is called and the
     global variable enter_special is true:

	   int enter_special;

	   %x SPECIAL
	   %%
		   if (enter_special)
			   BEGIN(SPECIAL);

	   <SPECIAL>blahblahblah
	   ...more rules follow...

     To illustrate the uses of start conditions, here is a scanner which
     provides two different interpretations of a string like "123.456".	 By
     default it will treat it as three tokens: the integer "123", a dot (`.'),
     and the integer "456".  But if the string is preceded earlier in the line
     by the string "expect-floats" it will treat it as a single token, the
     floating-point number 123.456:

	   %{
	   #include <math.h>
	   %}
	   %s expect

	   %%
	   expect-floats	BEGIN(expect);

	   <expect>[0-9]+"."[0-9]+ {
		   printf("found a float, = %f\n",
		       atof(yytext));
	   }
	   <expect>\n {
		   /*
		    * That's the end of the line, so
		    * we need another "expect-number"
		    * before we'll recognize any more
		    * numbers.
		    */
		   BEGIN(INITIAL);
	   }

	   [0-9]+ {
		   printf("found an integer, = %d\n",
		       atoi(yytext));
	   }

	   "."	   printf("found a dot\n");

     Here is a scanner which recognizes (and discards) C comments while
     maintaining a count of the current input line:

	   %x comment
	   %%
	   int line_num = 1;

	   "/*"			   BEGIN(comment);

	   <comment>[^*\n]*	   /* eat anything that's not a '*' */
	   <comment>"*"+[^*/\n]*   /* eat up '*'s not followed by '/'s */
	   <comment>\n		   ++line_num;
	   <comment>"*"+"/"	   BEGIN(INITIAL);

     This scanner goes to a bit of trouble to match as much text as possible
     with each rule.  In general, when attempting to write a high-speed
     scanner try to match as much as possible in each rule, as it's a big win.

     Note that start-condition names are really integer values and can be
     stored as such.  Thus, the above could be extended in the following
     fashion:

	   %x comment foo
	   %%
	   int line_num = 1;
	   int comment_caller;

	   "/*" {
		   comment_caller = INITIAL;
		   BEGIN(comment);
	   }

	   ...

	   <foo>"/*" {
		   comment_caller = foo;
		   BEGIN(comment);
	   }

	   <comment>[^*\n]*	   /* eat anything that's not a '*' */
	   <comment>"*"+[^*/\n]*   /* eat up '*'s not followed by '/'s */
	   <comment>\n		   ++line_num;
	   <comment>"*"+"/"	   BEGIN(comment_caller);

     Furthermore, the current start condition can be accessed by using the
     integer-valued YY_START macro.  For example, the above assignments to
     comment_caller could instead be written

	   comment_caller = YY_START;

     Flex provides YYSTATE as an alias for YY_START (since that is what's used
     by AT&T lex).

     Note that start conditions do not have their own name-space; %s's and
     %x's declare names in the same fashion as #define's.

     Finally, here's an example of how to match C-style quoted strings using
     exclusive start conditions, including expanded escape sequences (but not
     including checking for a string that's too long):

	   %x str

	   %%
	   #define MAX_STR_CONST 1024
	   char string_buf[MAX_STR_CONST];
	   char *string_buf_ptr;

	   \"	   string_buf_ptr = string_buf; BEGIN(str);

	   <str>\" { /* saw closing quote - all done */
		   BEGIN(INITIAL);
		   *string_buf_ptr = '\0';
		   /*
		    * return string constant token type and
		    * value to parser
		    */
	   }

	   <str>\n {
		   /* error - unterminated string constant */
		   /* generate error message */
	   }

	   <str>\\[0-7]{1,3} {
		   /* octal escape sequence */
		   int result;

		   (void) sscanf(yytext + 1, "%o", &result);

		   if (result > 0xff) {
			   /* error, constant is out-of-bounds */
		   } else
			   *string_buf_ptr++ = result;
	   }

	   <str>\\[0-9]+ {
		   /*
		    * generate error - bad escape sequence; something
		    * like '\48' or '\0777777'
		    */
	   }

	   <str>\\n  *string_buf_ptr++ = '\n';
	   <str>\\t  *string_buf_ptr++ = '\t';
	   <str>\\r  *string_buf_ptr++ = '\r';
	   <str>\\b  *string_buf_ptr++ = '\b';
	   <str>\\f  *string_buf_ptr++ = '\f';

	   <str>\\(.|\n)  *string_buf_ptr++ = yytext[1];

	   <str>[^\\\n\"]+ {
		   char *yptr = yytext;

		   while (*yptr)
			   *string_buf_ptr++ = *yptr++;
	   }

     Often, such as in some of the examples above, a whole bunch of rules are
     all preceded by the same start condition(s).  flex makes this a little
     easier and cleaner by introducing a notion of start condition scope.  A
     start condition scope is begun with:

	   <SCs>{

     where ``SCs'' is a list of one or more start conditions.  Inside the
     start condition scope, every rule automatically has the prefix <SCs>
     applied to it, until a `}' which matches the initial `{'.	So, for
     example,

	   <ESC>{
	       "\\n"   return '\n';
	       "\\r"   return '\r';
	       "\\f"   return '\f';
	       "\\0"   return '\0';
	   }

     is equivalent to:

	   <ESC>"\\n"  return '\n';
	   <ESC>"\\r"  return '\r';
	   <ESC>"\\f"  return '\f';
	   <ESC>"\\0"  return '\0';

     Start condition scopes may be nested.

     Three routines are available for manipulating stacks of start conditions:

     void yy_push_state(int new_state)
	     Pushes the current start condition onto the top of the start
	     condition stack and switches to new_state as though ``BEGIN
	     new_state'' had been used (recall that start condition names are
	     also integers).

     void yy_pop_state()
	     Pops the top of the stack and switches to it via BEGIN.

     int yy_top_state()
	     Returns the top of the stack without altering the stack's
	     contents.

     The start condition stack grows dynamically and so has no built-in size
     limitation.  If memory is exhausted, program execution aborts.

     To use start condition stacks, scanners must include a ``%option stack''
     directive (see OPTIONS below).

MULTIPLE INPUT BUFFERS
     Some scanners (such as those which support "include" files) require
     reading from several input streams.  As flex scanners do a large amount
     of buffering, one cannot control where the next input will be read from
     by simply writing a YY_INPUT which is sensitive to the scanning context.
     YY_INPUT is only called when the scanner reaches the end of its buffer,
     which may be a long time after scanning a statement such as an "include"
     which requires switching the input source.

     To negotiate these sorts of problems, flex provides a mechanism for
     creating and switching between multiple input buffers.  An input buffer
     is created by using:

	   YY_BUFFER_STATE yy_create_buffer(FILE *file, int size)

     which takes a FILE pointer and a size and creates a buffer associated
     with the given file and large enough to hold size characters (when in
     doubt, use YY_BUF_SIZE for the size).  It returns a YY_BUFFER_STATE
     handle, which may then be passed to other routines (see below).  The
     YY_BUFFER_STATE type is a pointer to an opaque ``struct yy_buffer_state''
     structure, so YY_BUFFER_STATE variables may be safely initialized to
     ``((YY_BUFFER_STATE) 0)'' if desired, and the opaque structure can also
     be referred to in order to correctly declare input buffers in source
     files other than that of scanners.	 Note that the FILE pointer in the
     call to yy_create_buffer() is only used as the value of yyin seen by
     YY_INPUT; if YY_INPUT is redefined so that it no longer uses yyin, then a
     nil FILE pointer can safely be passed to yy_create_buffer().  To select a
     particular buffer to scan:

	   void yy_switch_to_buffer(YY_BUFFER_STATE new_buffer)

     It switches the scanner's input buffer so subsequent tokens will come
     from new_buffer.  Note that yy_switch_to_buffer() may be used by yywrap()
     to set things up for continued scanning, instead of opening a new file
     and pointing yyin at it.  Note also that switching input sources via
     either yy_switch_to_buffer() or yywrap() does not change the start
     condition.

	   void yy_delete_buffer(YY_BUFFER_STATE buffer)

     is used to reclaim the storage associated with a buffer.  (buffer can be
     nil, in which case the routine does nothing.)  To clear the current
     contents of a buffer:

	   void yy_flush_buffer(YY_BUFFER_STATE buffer)

     This function discards the buffer's contents, so the next time the
     scanner attempts to match a token from the buffer, it will first fill the
     buffer anew using YY_INPUT.

     yy_new_buffer() is an alias for yy_create_buffer(), provided for
     compatibility with the C++ use of new and delete for creating and
     destroying dynamic objects.

     Finally, the YY_CURRENT_BUFFER macro returns a YY_BUFFER_STATE handle to
     the current buffer.

     Here is an example of using these features for writing a scanner which
     expands include files (the <<EOF>> feature is discussed below):

	   /*
	    * the "incl" state is used for picking up the name
	    * of an include file
	    */
	   %x incl

	   %{
	   #define MAX_INCLUDE_DEPTH 10
	   YY_BUFFER_STATE include_stack[MAX_INCLUDE_DEPTH];
	   int include_stack_ptr = 0;
	   %}

	   %%
	   include	       BEGIN(incl);

	   [a-z]+	       ECHO;
	   [^a-z\n]*\n?	       ECHO;

	   <incl>[ \t]*	       /* eat the whitespace */
	   <incl>[^ \t\n]+ {   /* got the include file name */
		   if (include_stack_ptr >= MAX_INCLUDE_DEPTH)
			   errx(1, "Includes nested too deeply");

		   include_stack[include_stack_ptr++] =
		       YY_CURRENT_BUFFER;

		   yyin = fopen(yytext, "r");

		   if (yyin == NULL)
			   err(1, NULL);

		   yy_switch_to_buffer(
		       yy_create_buffer(yyin, YY_BUF_SIZE));

		   BEGIN(INITIAL);
	   }

	   <<EOF>> {
		   if (--include_stack_ptr < 0)
			   yyterminate();
		   else {
			   yy_delete_buffer(YY_CURRENT_BUFFER);
			   yy_switch_to_buffer(
			       include_stack[include_stack_ptr]);
		  }
	   }

     Three routines are available for setting up input buffers for scanning
     in-memory strings instead of files.  All of them create a new input
     buffer for scanning the string, and return a corresponding
     YY_BUFFER_STATE handle (which should be deleted afterwards using
     yy_delete_buffer()).  They also switch to the new buffer using
     yy_switch_to_buffer(), so the next call to yylex() will start scanning
     the string.

     yy_scan_string(const char *str)
	     Scans a NUL-terminated string.

     yy_scan_bytes(const char *bytes, int len)
	     Scans len bytes (including possibly NUL's) starting at location
	     bytes.

     Note that both of these functions create and scan a copy of the string or
     bytes.  (This may be desirable, since yylex() modifies the contents of
     the buffer it is scanning.)  The copy can be avoided by using:

     yy_scan_buffer(char *base, yy_size_t size)
	     Which scans the buffer starting at base, consisting of size
	     bytes, the last two bytes of which must be YY_END_OF_BUFFER_CHAR
	     (ASCII NUL).  These last two bytes are not scanned; thus,
	     scanning consists of base[0] through base[size-2], inclusive.

	     If base is not set up in this manner (i.e., forget the final two
	     YY_END_OF_BUFFER_CHAR bytes), then yy_scan_buffer() returns a nil
	     pointer instead of creating a new input buffer.

	     The type yy_size_t is an integral type which can be cast to an
	     integer expression reflecting the size of the buffer.

END-OF-FILE RULES
     The special rule "<<EOF>>" indicates actions which are to be taken when
     an end-of-file is encountered and yywrap() returns non-zero (i.e.,
     indicates no further files to process).  The action must finish by doing
     one of four things:

     -	 Assigning yyin to a new input file (in previous versions of flex,
	 after doing the assignment, it was necessary to call the special
	 action YY_NEW_FILE; this is no longer necessary).

     -	 Executing a return statement.

     -	 Executing the special yyterminate() action.

     -	 Switching to a new buffer using yy_switch_to_buffer() as shown in the
	 example above.

     <<EOF>> rules may not be used with other patterns; they may only be
     qualified with a list of start conditions.	 If an unqualified <<EOF>>
     rule is given, it applies to all start conditions which do not already
     have <<EOF>> actions.  To specify an <<EOF>> rule for only the initial
     start condition, use

	   <INITIAL><<EOF>>

     These rules are useful for catching things like unclosed comments.	 An
     example:

	   %x quote
	   %%

	   ...other rules for dealing with quotes...

	   <quote><<EOF>> {
		    error("unterminated quote");
		    yyterminate();
	   }
	   <<EOF>> {
		    if (*++filelist)
			    yyin = fopen(*filelist, "r");
		    else
			    yyterminate();
	   }

MISCELLANEOUS MACROS
     The macro YY_USER_ACTION can be defined to provide an action which is
     always executed prior to the matched rule's action.  For example, it
     could be #define'd to call a routine to convert yytext to lower-case.
     When YY_USER_ACTION is invoked, the variable yy_act gives the number of
     the matched rule (rules are numbered starting with 1).  For example, to
     profile how often each rule is matched, the following would do the trick:

	   #define YY_USER_ACTION ++ctr[yy_act]

     where ctr is an array to hold the counts for the different rules.	Note
     that the macro YY_NUM_RULES gives the total number of rules (including
     the default rule, even if -s is used), so a correct declaration for ctr
     is:

	   int ctr[YY_NUM_RULES];

     The macro YY_USER_INIT may be defined to provide an action which is
     always executed before the first scan (and before the scanner's internal
     initializations are done).	 For example, it could be used to call a
     routine to read in a data table or open a logging file.

     The macro yy_set_interactive(is_interactive) can be used to control
     whether the current buffer is considered interactive.  An interactive
     buffer is processed more slowly, but must be used when the scanner's
     input source is indeed interactive to avoid problems due to waiting to
     fill buffers (see the discussion of the -I flag below).  A non-zero value
     in the macro invocation marks the buffer as interactive, a zero value as
     non-interactive.  Note that use of this macro overrides ``%option
     always-interactive'' or ``%option never-interactive'' (see OPTIONS
     below).  yy_set_interactive() must be invoked prior to beginning to scan
     the buffer that is (or is not) to be considered interactive.

     The macro yy_set_bol(at_bol) can be used to control whether the current
     buffer's scanning context for the next token match is done as though at
     the beginning of a line.  A non-zero macro argument makes rules anchored
     with `^' active, while a zero argument makes `^' rules inactive.

     The macro YY_AT_BOL returns true if the next token scanned from the
     current buffer will have `^' rules active, false otherwise.

     In the generated scanner, the actions are all gathered in one large
     switch statement and separated using YY_BREAK, which may be redefined.
     By default, it is simply a "break", to separate each rule's action from
     the following rules.  Redefining YY_BREAK allows, for example, C++ users
     to ``#define YY_BREAK'' to do nothing (while being very careful that
     every rule ends with a "break" or a "return"!) to avoid suffering from
     unreachable statement warnings where because a rule's action ends with
     ``return'', the YY_BREAK is inaccessible.

VALUES AVAILABLE TO THE USER
     This section summarizes the various values available to the user in the
     rule actions.

     char *yytext
	     Holds the text of the current token.  It may be modified but not
	     lengthened (characters cannot be appended to the end).

	     If the special directive ``%array'' appears in the first section
	     of the scanner description, then yytext is instead declared
	     ``char yytext[YYLMAX]'', where YYLMAX is a macro definition that
	     can be redefined in the first section to change the default value
	     (generally 8KB).  Using ``%array'' results in somewhat slower
	     scanners, but the value of yytext becomes immune to calls to
	     input() and unput(), which potentially destroy its value when
	     yytext is a character pointer.  The opposite of ``%array'' is
	     ``%pointer'', which is the default.

	     ``%array'' cannot be used when generating C++ scanner classes
	     (the -+ flag).

     int yyleng
	     Holds the length of the current token.

     FILE *yyin
	     Is the file which by default flex reads from.  It may be
	     redefined, but doing so only makes sense before scanning begins
	     or after an EOF has been encountered.  Changing it in the midst
	     of scanning will have unexpected results since flex buffers its
	     input; use yyrestart() instead.  Once scanning terminates because
	     an end-of-file has been seen, yyin can be assigned as the new
	     input file and the scanner can be called again to continue
	     scanning.

     void yyrestart(FILE *new_file)
	     May be called to point yyin at the new input file.	 The switch-
	     over to the new file is immediate (any previously buffered-up
	     input is lost).  Note that calling yyrestart() with yyin as an
	     argument thus throws away the current input buffer and continues
	     scanning the same input file.

     FILE *yyout
	     Is the file to which ECHO actions are done.  It can be reassigned
	     by the user.

     YY_CURRENT_BUFFER
	     Returns a YY_BUFFER_STATE handle to the current buffer.

     YY_START
	     Returns an integer value corresponding to the current start
	     condition.	 This value can subsequently be used with BEGIN to
	     return to that start condition.

INTERFACING WITH YACC
     One of the main uses of flex is as a companion to the yacc(1) parser-
     generator.	 yacc parsers expect to call a routine named yylex() to find
     the next input token.  The routine is supposed to return the type of the
     next token as well as putting any associated value in the global yylval,
     which is defined externally, and can be a union or any other complex data
     structure.	 To use flex with yacc, one specifies the -d option to yacc to
     instruct it to generate the file y.tab.h containing definitions of all
     the ``%tokens'' appearing in the yacc input.  This file is then included
     in the flex scanner.  For example, if one of the tokens is "TOK_NUMBER",
     part of the scanner might look like:

	   %{
	   #include "y.tab.h"
	   %}

	   %%

	   [0-9]+	 yylval = atoi(yytext); return TOK_NUMBER;

OPTIONS
     flex has the following options:

     -7	     Instructs flex to generate a 7-bit scanner, i.e., one which can
	     only recognize 7-bit characters in its input.  The advantage of
	     using -7 is that the scanner's tables can be up to half the size
	     of those generated using the -8 option (see below).  The
	     disadvantage is that such scanners often hang or crash if their
	     input contains an 8-bit character.

	     Note, however, that unless generating a scanner using the -Cf or
	     -CF table compression options, use of -7 will save only a small
	     amount of table space, and make the scanner considerably less
	     portable.	flex's default behavior is to generate an 8-bit
	     scanner unless -Cf or -CF is specified, in which case flex
	     defaults to generating 7-bit scanners unless it was configured to
	     generate 8-bit scanners (as will often be the case with non-USA
	     sites).  It is possible tell whether flex generated a 7-bit or an
	     8-bit scanner by inspecting the flag summary in the -v output as
	     described below.

	     Note that if -Cfe or -CFe are used (the table compression
	     options, but also using equivalence classes as discussed below),
	     flex still defaults to generating an 8-bit scanner, since usually
	     with these compression options full 8-bit tables are not much
	     more expensive than 7-bit tables.

     -8	     Instructs flex to generate an 8-bit scanner, i.e., one which can
	     recognize 8-bit characters.  This flag is only needed for
	     scanners generated using -Cf or -CF, as otherwise flex defaults
	     to generating an 8-bit scanner anyway.

	     See the discussion of -7 above for flex's default behavior and
	     the tradeoffs between 7-bit and 8-bit scanners.

     -B	     Instructs flex to generate a batch scanner, the opposite of
	     interactive scanners generated by -I (see below).	In general, -B
	     is used when the scanner will never be used interactively, and
	     you want to squeeze a little more performance out of it.  If the
	     aim is instead to squeeze out a lot more performance, use the -Cf
	     or -CF options (discussed below), which turn on -B automatically
	     anyway.

     -b	     Generate backing-up information to lex.backup.  This is a list of
	     scanner states which require backing up and the input characters
	     on which they do so.  By adding rules one can remove backing-up
	     states.  If all backing-up states are eliminated and -Cf or -CF
	     is used, the generated scanner will run faster (see the -p flag).
	     Only users who wish to squeeze every last cycle out of their
	     scanners need worry about this option.  (See the section on
	     PERFORMANCE CONSIDERATIONS below.)

     -C[aeFfmr]
	     Controls the degree of table compression and, more generally,
	     trade-offs between small scanners and fast scanners.

	     -Ca     Instructs flex to trade off larger tables in the
		     generated scanner for faster performance because the
		     elements of the tables are better aligned for memory
		     access and computation.  On some RISC architectures,
		     fetching and manipulating longwords is more efficient
		     than with smaller-sized units such as shortwords.	This
		     option can double the size of the tables used by the
		     scanner.

	     -Ce     Directs flex to construct equivalence classes, i.e., sets
		     of characters which have identical lexical properties
		     (for example, if the only appearance of digits in the
		     flex input is in the character class "[0-9]" then the
		     digits `0', `1', `...', `9' will all be put in the same
		     equivalence class).  Equivalence classes usually give
		     dramatic reductions in the final table/object file sizes
		     (typically a factor of 2-5) and are pretty cheap
		     performance-wise (one array look-up per character
		     scanned).

	     -CF     Specifies that the alternate fast scanner representation
		     (described below under the -F option) should be used.
		     This option cannot be used with -+.

	     -Cf     Specifies that the full scanner tables should be
		     generated - flex should not compress the tables by taking
		     advantage of similar transition functions for different
		     states.

	     -Cm     Directs flex to construct meta-equivalence classes, which
		     are sets of equivalence classes (or characters, if
		     equivalence classes are not being used) that are commonly
		     used together.  Meta-equivalence classes are often a big
		     win when using compressed tables, but they have a
		     moderate performance impact (one or two "if" tests and
		     one array look-up per character scanned).

	     -Cr     Causes the generated scanner to bypass use of the
		     standard I/O library (stdio) for input.  Instead of
		     calling fread(3) or getc(3), the scanner will use the
		     read(2) system call, resulting in a performance gain
		     which varies from system to system, but in general is
		     probably negligible unless -Cf or -CF are being used.
		     Using -Cr can cause strange behavior if, for example,
		     reading from yyin using stdio prior to calling the
		     scanner (because the scanner will miss whatever text
		     previous reads left in the stdio input buffer).

		     -Cr has no effect if YY_INPUT is defined (see THE
		     GENERATED SCANNER above).

	     A lone -C specifies that the scanner tables should be compressed
	     but neither equivalence classes nor meta-equivalence classes
	     should be used.

	     The options -Cf or -CF and -Cm do not make sense together - there
	     is no opportunity for meta-equivalence classes if the table is
	     not being compressed.  Otherwise the options may be freely mixed,
	     and are cumulative.

	     The default setting is -Cem which specifies that flex should
	     generate equivalence classes and meta-equivalence classes.	 This
	     setting provides the highest degree of table compression.	It is
	     possible to trade off faster-executing scanners at the cost of
	     larger tables with the following generally being true:

		   slowest & smallest
			 -Cem
			 -Cm
			 -Ce
			 -C
			 -C{f,F}e
			 -C{f,F}
			 -C{f,F}a
		   fastest & largest

	     Note that scanners with the smallest tables are usually generated
	     and compiled the quickest, so during development the default is
	     usually best, maximal compression.

	     -Cfe is often a good compromise between speed and size for
	     production scanners.

     -c	     A do-nothing, deprecated option included for POSIX compliance.

     -d	     Makes the generated scanner run in debug mode.  Whenever a
	     pattern is recognized and the global yy_flex_debug is non-zero
	     (which is the default), the scanner will write to stderr a line
	     of the form:

		   --accepting rule at line 53 ("the matched text")

	     The line number refers to the location of the rule in the file
	     defining the scanner (i.e., the file that was fed to flex).
	     Messages are also generated when the scanner backs up, accepts
	     the default rule, reaches the end of its input buffer (or
	     encounters a NUL; at this point, the two look the same as far as
	     the scanner's concerned), or reaches an end-of-file.

     -F	     Specifies that the fast scanner table representation should be
	     used (and stdio bypassed).	 This representation is about as fast
	     as the full table representation (-f), and for some sets of
	     patterns will be considerably smaller (and for others, larger).
	     In general, if the pattern set contains both "keywords" and a
	     catch-all, "identifier" rule, such as in the set:

		   "case"    return TOK_CASE;
		   "switch"  return TOK_SWITCH;
		   ...
		   "default" return TOK_DEFAULT;
		   [a-z]+    return TOK_ID;

	     then it's better to use the full table representation.  If only
	     the "identifier" rule is present and a hash table or some such is
	     used to detect the keywords, it's better to use -F.

	     This option is equivalent to -CFr (see above).  It cannot be used
	     with -+.

     -f	     Specifies fast scanner.  No table compression is done and stdio
	     is bypassed.  The result is large but fast.  This option is
	     equivalent to -Cfr (see above).

     -h	     Generates a help summary of flex's options to stdout and then
	     exits.  -? and --help are synonyms for -h.

     -I	     Instructs flex to generate an interactive scanner.	 An
	     interactive scanner is one that only looks ahead to decide what
	     token has been matched if it absolutely must.  It turns out that
	     always looking one extra character ahead, even if the scanner has
	     already seen enough text to disambiguate the current token, is a
	     bit faster than only looking ahead when necessary.	 But scanners
	     that always look ahead give dreadful interactive performance; for
	     example, when a user types a newline, it is not recognized as a
	     newline token until they enter another token, which often means
	     typing in another whole line.

	     flex scanners default to interactive unless -Cf or -CF table-
	     compression options are specified (see above).  That's because if
	     high-performance is most important, one of these options should
	     be used, so if they weren't, flex assumes it is preferable to
	     trade off a bit of run-time performance for intuitive interactive
	     behavior.	Note also that -I cannot be used in conjunction with
	     -Cf or -CF.  Thus, this option is not really needed; it is on by
	     default for all those cases in which it is allowed.

	     A scanner can be forced to not be interactive by using -B (see
	     above).

     -i	     Instructs flex to generate a case-insensitive scanner.  The case
	     of letters given in the flex input patterns will be ignored, and
	     tokens in the input will be matched regardless of case.  The
	     matched text given in yytext will have the preserved case (i.e.,
	     it will not be folded).

     -L	     Instructs flex not to generate ``#line'' directives.  Without
	     this option, flex peppers the generated scanner with #line
	     directives so error messages in the actions will be correctly
	     located with respect to either the original flex input file (if
	     the errors are due to code in the input file), or lex.yy.c (if
	     the errors are flex's fault - these sorts of errors should be
	     reported to the email address given below).

     -l	     Turns on maximum compatibility with the original AT&T lex
	     implementation.  Note that this does not mean full compatibility.
	     Use of this option costs a considerable amount of performance,
	     and it cannot be used with the -+, -f, -F, -Cf, or -CF options.
	     For details on the compatibilities it provides, see the section
	     INCOMPATIBILITIES WITH LEX AND POSIX below.  This option also
	     results in the name YY_FLEX_LEX_COMPAT being #define'd in the
	     generated scanner.

     -n	     Another do-nothing, deprecated option included only for POSIX
	     compliance.

     -ooutput
	     Directs flex to write the scanner to the file output instead of
	     lex.yy.c.	If -o is combined with the -t option, then the scanner
	     is written to stdout but its ``#line'' directives (see the -L
	     option above) refer to the file output.

     -Pprefix
	     Changes the default "yy" prefix used by flex for all globally
	     visible variable and function names to instead be prefix.	For
	     example, -Pfoo changes the name of yytext to footext.  It also
	     changes the name of the default output file from lex.yy.c to
	     lex.foo.c.	 Here are all of the names affected:

		   yy_create_buffer
		   yy_delete_buffer
		   yy_flex_debug
		   yy_init_buffer
		   yy_flush_buffer
		   yy_load_buffer_state
		   yy_switch_to_buffer
		   yyin
		   yyleng
		   yylex
		   yylineno
		   yyout
		   yyrestart
		   yytext
		   yywrap

	     (If using a C++ scanner, then only yywrap and yyFlexLexer are
	     affected.)	 Within the scanner itself, it is still possible to
	     refer to the global variables and functions using either version
	     of their name; but externally, they have the modified name.

	     This option allows multiple flex programs to be easily linked
	     together into the same executable.	 Note, though, that using this
	     option also renames yywrap(), so now either an (appropriately
	     named) version of the routine for the scanner must be supplied,
	     or ``%option noyywrap'' must be used, as linking with -lfl no
	     longer provides one by default.

     -p	     Generates a performance report to stderr.	The report consists of
	     comments regarding features of the flex input file which will
	     cause a serious loss of performance in the resulting scanner.  If
	     the flag is specified twice, comments regarding features that
	     lead to minor performance losses will also be reported>

	     Note that the use of REJECT, ``%option yylineno'', and variable
	     trailing context (see the BUGS section below) entails a
	     substantial performance penalty; use of yymore(), the `^'
	     operator, and the -I flag entail minor performance penalties.

     -Sskeleton
	     Overrides the default skeleton file from which flex constructs
	     its scanners.  This option is needed only for flex maintenance or
	     development.

     -s	     Causes the default rule (that unmatched scanner input is echoed
	     to stdout) to be suppressed.  If the scanner encounters input
	     that does not match any of its rules, it aborts with an error.
	     This option is useful for finding holes in a scanner's rule set.

     -T	     Makes flex run in trace mode.  It will generate a lot of messages
	     to stderr concerning the form of the input and the resultant non-
	     deterministic and deterministic finite automata.  This option is
	     mostly for use in maintaining flex.

     -t	     Instructs flex to write the scanner it generates to standard
	     output instead of lex.yy.c.

     -V	     Prints the version number to stdout and exits.  --version is a
	     synonym for -V.

     -v	     Specifies that flex should write to stderr a summary of
	     statistics regarding the scanner it generates.  Most of the
	     statistics are meaningless to the casual flex user, but the first
	     line identifies the version of flex (same as reported by -V), and
	     the next line the flags used when generating the scanner,
	     including those that are on by default.

     -w	     Suppresses warning messages.

     -+	     Specifies that flex should generate a C++ scanner class.  See the
	     section on GENERATING C++ SCANNERS below for details.

     flex also provides a mechanism for controlling options within the scanner
     specification itself, rather than from the flex command-line.  This is
     done by including ``%option'' directives in the first section of the
     scanner specification.  Multiple options can be specified with a single
     ``%option'' directive, and multiple directives in the first section of
     the flex input file.

     Most options are given simply as names, optionally preceded by the word
     "no" (with no intervening whitespace) to negate their meaning.  A number
     are equivalent to flex flags or their negation:

	   7bit		   -7 option
	   8bit		   -8 option
	   align	   -Ca option
	   backup	   -b option
	   batch	   -B option
	   c++		   -+ option

	   caseful or
	   case-sensitive  opposite of -i (default)

	   case-insensitive or
	   caseless	   -i option

	   debug	   -d option
	   default	   opposite of -s option
	   ecs		   -Ce option
	   fast		   -F option
	   full		   -f option
	   interactive	   -I option
	   lex-compat	   -l option
	   meta-ecs	   -Cm option
	   perf-report	   -p option
	   read		   -Cr option
	   stdout	   -t option
	   verbose	   -v option
	   warn		   opposite of -w option
			   (use "%option nowarn" for -w)

	   array	   equivalent to "%array"
	   pointer	   equivalent to "%pointer" (default)

     Some %option's provide features otherwise not available:

     always-interactive
	     Instructs flex to generate a scanner which always considers its
	     input "interactive".  Normally, on each new input file the
	     scanner calls isatty() in an attempt to determine whether the
	     scanner's input source is interactive and thus should be read a
	     character at a time.  When this option is used, however, no such
	     call is made.

     main    Directs flex to provide a default main() program for the scanner,
	     which simply calls yylex().  This option implies ``noyywrap''
	     (see below).

     never-interactive
	     Instructs flex to generate a scanner which never considers its
	     input "interactive" (again, no call made to isatty()).  This is
	     the opposite of ``always-interactive''.

     stack   Enables the use of start condition stacks (see START CONDITIONS
	     above).

     stdinit
	     If set (i.e., ``%option stdinit''), initializes yyin and yyout to
	     stdin and stdout, instead of the default of ``nil''.  Some
	     existing lex programs depend on this behavior, even though it is
	     not compliant with ANSI C, which does not require stdin and
	     stdout to be compile-time constant.

     yylineno
	     Directs flex to generate a scanner that maintains the number of
	     the current line read from its input in the global variable
	     yylineno.	This option is implied by ``%option lex-compat''.

     yywrap  If unset (i.e., ``%option noyywrap''), makes the scanner not call
	     yywrap() upon an end-of-file, but simply assume that there are no
	     more files to scan (until the user points yyin at a new file and
	     calls yylex() again).

     flex scans rule actions to determine whether the REJECT or yymore()
     features are being used.  The ``reject'' and ``yymore'' options are
     available to override its decision as to whether to use the options,
     either by setting them (e.g., ``%option reject'') to indicate the feature
     is indeed used, or unsetting them to indicate it actually is not used
     (e.g., ``%option noyymore'').

     Three options take string-delimited values, offset with `=':

	   %option outfile="ABC"

     is equivalent to -oABC, and

	   %option prefix="XYZ"

     is equivalent to -PXYZ.  Finally,

	   %option yyclass="foo"

     only applies when generating a C++ scanner (-+ option).  It informs flex
     that ``foo'' has been derived as a subclass of yyFlexLexer, so flex will
     place actions in the member function ``foo::yylex()'' instead of
     ``yyFlexLexer::yylex()''.	It also generates a ``yyFlexLexer::yylex()''
     member function that emits a run-time error (by invoking
     ``yyFlexLexer::LexerError()'') if called.	See GENERATING C++ SCANNERS,
     below, for additional information.

     A number of options are available for lint(1) purists who want to
     suppress the appearance of unneeded routines in the generated scanner.
     Each of the following, if unset (e.g., ``%option nounput''), results in
     the corresponding routine not appearing in the generated scanner:

	   input, unput
	   yy_push_state, yy_pop_state, yy_top_state
	   yy_scan_buffer, yy_scan_bytes, yy_scan_string

     (though yy_push_state() and friends won't appear anyway unless ``%option
     stack'' is being used).

PERFORMANCE CONSIDERATIONS
     The main design goal of flex is that it generate high-performance
     scanners.	It has been optimized for dealing well with large sets of
     rules.  Aside from the effects on scanner speed of the table compression
     -C options outlined above, there are a number of options/actions which
     degrade performance.  These are, from most expensive to least:

	   REJECT
	   %option yylineno
	   arbitrary trailing context

	   pattern sets that require backing up
	   %array
	   %option interactive
	   %option always-interactive

	   '^' beginning-of-line operator
	   yymore()

     with the first three all being quite expensive and the last two being
     quite cheap.  Note also that unput() is implemented as a routine call
     that potentially does quite a bit of work, while yyless() is a quite-
     cheap macro; so if just putting back some excess text, use yyless().

     REJECT should be avoided at all costs when performance is important.  It
     is a particularly expensive option.

     Getting rid of backing up is messy and often may be an enormous amount of
     work for a complicated scanner.  In principal, one begins by using the -b
     flag to generate a lex.backup file.  For example, on the input

	   %%
	   foo	      return TOK_KEYWORD;
	   foobar     return TOK_KEYWORD;

     the file looks like:

	   State #6 is non-accepting -
	    associated rule line numbers:
		  2	  3
	    out-transitions: [ o ]
	    jam-transitions: EOF [ \001-n  p-\177 ]

	   State #8 is non-accepting -
	    associated rule line numbers:
		  3
	    out-transitions: [ a ]
	    jam-transitions: EOF [ \001-`  b-\177 ]

	   State #9 is non-accepting -
	    associated rule line numbers:
		  3
	    out-transitions: [ r ]
	    jam-transitions: EOF [ \001-q  s-\177 ]

	   Compressed tables always back up.

     The first few lines tell us that there's a scanner state in which it can
     make a transition on an `o' but not on any other character, and that in
     that state the currently scanned text does not match any rule.  The state
     occurs when trying to match the rules found at lines 2 and 3 in the input
     file.  If the scanner is in that state and then reads something other
     than an `o', it will have to back up to find a rule which is matched.
     With a bit of headscratching one can see that this must be the state it's
     in when it has seen `fo'.	When this has happened, if anything other than
     another `o' is seen, the scanner will have to back up to simply match the
     `f' (by the default rule).

     The comment regarding State #8 indicates there's a problem when "foob"
     has been scanned.	Indeed, on any character other than an `a', the
     scanner will have to back up to accept "foo".  Similarly, the comment for
     State #9 concerns when "fooba" has been scanned and an `r' does not
     follow.

     The final comment reminds us that there's no point going to all the
     trouble of removing backing up from the rules unless we're using -Cf or
     -CF, since there's no performance gain doing so with compressed scanners.

     The way to remove the backing up is to add "error" rules:

	   %%
	   foo	  return TOK_KEYWORD;
	   foobar return TOK_KEYWORD;

	   fooba  |
	   foob	  |
	   fo {
		   /* false alarm, not really a keyword */
		   return TOK_ID;
	   }

     Eliminating backing up among a list of keywords can also be done using a
     "catch-all" rule:

	   %%
	   foo	  return TOK_KEYWORD;
	   foobar return TOK_KEYWORD;

	   [a-z]+ return TOK_ID;

     This is usually the best solution when appropriate.

     Backing up messages tend to cascade.  With a complicated set of rules
     it's not uncommon to get hundreds of messages.  If one can decipher them,
     though, it often only takes a dozen or so rules to eliminate the backing
     up (though it's easy to make a mistake and have an error rule
     accidentally match a valid token; a possible future flex feature will be
     to automatically add rules to eliminate backing up).

     It's important to keep in mind that the benefits of eliminating backing
     up are gained only if every instance of backing up is eliminated.
     Leaving just one gains nothing.

     Variable trailing context (where both the leading and trailing parts do
     not have a fixed length) entails almost the same performance loss as
     REJECT (i.e., substantial).  So when possible a rule like:

	   %%
	   mouse|rat/(cat|dog)	 run();

     is better written:

	   %%
	   mouse/cat|dog	 run();
	   rat/cat|dog		 run();

     or as

	   %%
	   mouse|rat/cat	 run();
	   mouse|rat/dog	 run();

     Note that here the special `|' action does not provide any savings, and
     can even make things worse (see BUGS below).

     Another area where the user can increase a scanner's performance (and one
     that's easier to implement) arises from the fact that the longer the
     tokens matched, the faster the scanner will run.  This is because with
     long tokens the processing of most input characters takes place in the
     (short) inner scanning loop, and does not often have to go through the
     additional work of setting up the scanning environment (e.g., yytext) for
     the action.  Recall the scanner for C comments:

	   %x comment
	   %%
	   int line_num = 1;

	   "/*"			   BEGIN(comment);

	   <comment>[^*\n]*
	   <comment>"*"+[^*/\n]*
	   <comment>\n		   ++line_num;
	   <comment>"*"+"/"	   BEGIN(INITIAL);

     This could be sped up by writing it as:

	   %x comment
	   %%
	   int line_num = 1;

	   "/*"			   BEGIN(comment);

	   <comment>[^*\n]*
	   <comment>[^*\n]*\n	   ++line_num;
	   <comment>"*"+[^*/\n]*
	   <comment>"*"+[^*/\n]*\n ++line_num;
	   <comment>"*"+"/"	   BEGIN(INITIAL);

     Now instead of each newline requiring the processing of another action,
     recognizing the newlines is "distributed" over the other rules to keep
     the matched text as long as possible.  Note that adding rules does not
     slow down the scanner!  The speed of the scanner is independent of the
     number of rules or (modulo the considerations given at the beginning of
     this section) how complicated the rules are with regard to operators such
     as `*' and `|'.

     A final example in speeding up a scanner: scan through a file containing
     identifiers and keywords, one per line and with no other extraneous
     characters, and recognize all the keywords.  A natural first approach is:

	   %%
	   asm	    |
	   auto	    |
	   break    |
	   ... etc ...
	   volatile |
	   while    /* it's a keyword */

	   .|\n	    /* it's not a keyword */

     To eliminate the back-tracking, introduce a catch-all rule:

	   %%
	   asm	    |
	   auto	    |
	   break    |
	   ... etc ...
	   volatile |
	   while    /* it's a keyword */

	   [a-z]+   |
	   .|\n	    /* it's not a keyword */

     Now, if it's guaranteed that there's exactly one word per line, then we
     can reduce the total number of matches by a half by merging in the
     recognition of newlines with that of the other tokens:

	   %%
	   asm\n      |
	   auto\n     |
	   break\n    |
	   ... etc ...
	   volatile\n |
	   while\n    /* it's a keyword */

	   [a-z]+\n   |
	   .|\n	      /* it's not a keyword */

     One has to be careful here, as we have now reintroduced backing up into
     the scanner.  In particular, while we know that there will never be any
     characters in the input stream other than letters or newlines, flex can't
     figure this out, and it will plan for possibly needing to back up when it
     has scanned a token like "auto" and then the next character is something
     other than a newline or a letter.	Previously it would then just match
     the "auto" rule and be done, but now it has no "auto" rule, only an
     "auto\n" rule.  To eliminate the possibility of backing up, we could
     either duplicate all rules but without final newlines, or, since we never
     expect to encounter such an input and therefore don't how it's
     classified, we can introduce one more catch-all rule, this one which
     doesn't include a newline:

	   %%
	   asm\n      |
	   auto\n     |
	   break\n    |
	   ... etc ...
	   volatile\n |
	   while\n    /* it's a keyword */

	   [a-z]+\n   |
	   [a-z]+     |
	   .|\n	      /* it's not a keyword */

     Compiled with -Cf, this is about as fast as one can get a flex scanner to
     go for this particular problem.

     A final note: flex is slow when matching NUL's, particularly when a token
     contains multiple NUL's.  It's best to write rules which match short
     amounts of text if it's anticipated that the text will often include
     NUL's.

     Another final note regarding performance: as mentioned above in the
     section HOW THE INPUT IS MATCHED, dynamically resizing yytext to
     accommodate huge tokens is a slow process because it presently requires
     that the (huge) token be rescanned from the beginning.  Thus if
     performance is vital, it is better to attempt to match "large" quantities
     of text but not "huge" quantities, where the cutoff between the two is at
     about 8K characters/token.

GENERATING C++ SCANNERS
     flex provides two different ways to generate scanners for use with C++.
     The first way is to simply compile a scanner generated by flex using a
     C++ compiler instead of a C compiler.  This should not generate any
     compilation errors (please report any found to the email address given in
     the AUTHORS section below).  C++ code can then be used in rule actions
     instead of C code.	 Note that the default input source for scanners
     remains yyin, and default echoing is still done to yyout.	Both of these
     remain FILE * variables and not C++ streams.

     flex can also be used to generate a C++ scanner class, using the -+
     option (or, equivalently, ``%option c++''), which is automatically
     specified if the name of the flex executable ends in a `+', such as
     flex++.  When using this option, flex defaults to generating the scanner
     to the file lex.yy.cc instead of lex.yy.c.	 The generated scanner
     includes the header file <g++/FlexLexer.h>, which defines the interface
     to two C++ classes.

     The first class, FlexLexer, provides an abstract base class defining the
     general scanner class interface.  It provides the following member
     functions:

     const char* YYText()
	     Returns the text of the most recently matched token, the
	     equivalent of yytext.

     int YYLeng()
	     Returns the length of the most recently matched token, the
	     equivalent of yyleng.

     int lineno() const
	     Returns the current input line number (see ``%option yylineno''),
	     or 1 if ``%option yylineno'' was not used.

     void set_debug(int flag)
	     Sets the debugging flag for the scanner, equivalent to assigning
	     to yy_flex_debug (see the OPTIONS section above).	Note that the
	     scanner must be built using ``%option debug'' to include
	     debugging information in it.

     int debug() const
	     Returns the current setting of the debugging flag.

     Also provided are member functions equivalent to yy_switch_to_buffer(),
     yy_create_buffer() (though the first argument is an std::istream* object
     pointer and not a FILE*), yy_flush_buffer(), yy_delete_buffer(), and
     yyrestart() (again, the first argument is an std::istream* object
     pointer).

     The second class defined in <g++/FlexLexer.h> is yyFlexLexer, which is
     derived from FlexLexer.  It defines the following additional member
     functions:

     yyFlexLexer(std::istream* arg_yyin = 0, std::ostream* arg_yyout = 0)
	     Constructs a yyFlexLexer object using the given streams for input
	     and output.  If not specified, the streams default to cin and
	     cout, respectively.

     virtual int yylex()
	     Performs the same role as yylex() does for ordinary flex
	     scanners: it scans the input stream, consuming tokens, until a
	     rule's action returns a value.  If subclass `S' is derived from
	     yyFlexLexer, in order to access the member functions and
	     variables of `S' inside yylex(), use ``%option yyclass="S"'' to
	     inform flex that the `S' subclass will be used instead of
	     yyFlexLexer.  In this case, rather than generating
	     ``yyFlexLexer::yylex()'', flex generates ``S::yylex()'' (and also
	     generates a dummy ``yyFlexLexer::yylex()'' that calls
	     ``yyFlexLexer::LexerError()'' if called).

     virtual void switch_streams(std::istream* new_in = 0, std::ostream*
	      new_out = 0)
	     Reassigns yyin to new_in (if non-nil) and yyout to new_out
	     (ditto), deleting the previous input buffer if yyin is
	     reassigned.

     int yylex(std::istream* new_in, std::ostream* new_out = 0)
	     First switches the input streams via ``switch_streams(new_in,
	     new_out)'' and then returns the value of yylex().

     In addition, yyFlexLexer defines the following protected virtual
     functions which can be redefined in derived classes to tailor the
     scanner:

     virtual int LexerInput(char* buf, int max_size)
	     Reads up to max_size characters into buf and returns the number
	     of characters read.  To indicate end-of-input, return 0
	     characters.  Note that "interactive" scanners (see the -B and -I
	     flags) define the macro YY_INTERACTIVE.  If LexerInput() has been
	     redefined, and it's necessary to take different actions depending
	     on whether or not the scanner might be scanning an interactive
	     input source, it's possible to test for the presence of this name
	     via ``#ifdef''.

     virtual void LexerOutput(const char* buf, int size)
	     Writes out size characters from the buffer buf, which, while NUL-
	     terminated, may also contain "internal" NUL's if the scanner's
	     rules can match text with NUL's in them.

     virtual void LexerError(const char* msg)
	     Reports a fatal error message.  The default version of this
	     function writes the message to the stream cerr and exits.

     Note that a yyFlexLexer object contains its entire scanning state.	 Thus
     such objects can be used to create reentrant scanners.  Multiple
     instances of the same yyFlexLexer class can be instantiated, and multiple
     C++ scanner classes can be combined in the same program using the -P
     option discussed above.

     Finally, note that the ``%array'' feature is not available to C++ scanner
     classes; ``%pointer'' must be used (the default).

     Here is an example of a simple C++ scanner:

	   // An example of using the flex C++ scanner class.

	   %{
	   #include <errno.h>
	   int mylineno = 0;
	   %}

	   string  \"[^\n"]+\"

	   ws	   [ \t]+

	   alpha   [A-Za-z]
	   dig	   [0-9]
	   name	   ({alpha}|{dig}|\$)({alpha}|{dig}|[_.\-/$])*
	   num1	   [-+]?{dig}+\.?([eE][-+]?{dig}+)?
	   num2	   [-+]?{dig}*\.{dig}+([eE][-+]?{dig}+)?
	   number  {num1}|{num2}

	   %%

	   {ws}	   /* skip blanks and tabs */

	   "/*" {
		   int c;

		   while ((c = yyinput()) != 0) {
			   if(c == '\n')
			       ++mylineno;
			   else if(c == '*') {
			       if ((c = yyinput()) == '/')
				   break;
			       else
				   unput(c);
			   }
		   }
	   }

	   {number}  cout << "number " << YYText() << '\n';

	   \n	     mylineno++;

	   {name}    cout << "name " << YYText() << '\n';

	   {string}  cout << "string " << YYText() << '\n';

	   %%

	   int main(int /* argc */, char** /* argv */)
	   {
		   FlexLexer* lexer = new yyFlexLexer;
		   while(lexer->yylex() != 0)
		       ;
		   return 0;
	   }

     To create multiple (different) lexer classes, use the -P flag (or the
     ``prefix='' option) to rename each yyFlexLexer to some other xxFlexLexer.
     <g++/FlexLexer.h> can then be included in other sources once per lexer
     class, first renaming yyFlexLexer as follows:

	   #undef yyFlexLexer
	   #define yyFlexLexer xxFlexLexer
	   #include <g++/FlexLexer.h>

	   #undef yyFlexLexer
	   #define yyFlexLexer zzFlexLexer
	   #include <g++/FlexLexer.h>

     If, for example, ``%option prefix="xx"'' is used for one scanner and
     ``%option prefix="zz"'' is used for the other.

     IMPORTANT: the present form of the scanning class is experimental and may
     change considerably between major releases.

INCOMPATIBILITIES WITH LEX AND POSIX
     flex is a rewrite of the AT&T UNIX lex tool (the two implementations do
     not share any code, though), with some extensions and incompatibilities,
     both of which are of concern to those who wish to write scanners
     acceptable to either implementation.  flex is fully compliant with the
     POSIX lex specification, except that when using ``%pointer'' (the
     default), a call to unput() destroys the contents of yytext, which is
     counter to the POSIX specification.

     In this section we discuss all of the known areas of incompatibility
     between flex, AT&T lex, and the POSIX specification.

     flex's -l option turns on maximum compatibility with the original AT&T
     lex implementation, at the cost of a major loss in the generated
     scanner's performance.  We note below which incompatibilities can be
     overcome using the -l option.

     flex is fully compatible with lex with the following exceptions:

     -	 The undocumented lex scanner internal variable yylineno is not
	 supported unless -l or ``%option yylineno'' is used.

	 yylineno should be maintained on a per-buffer basis, rather than a
	 per-scanner (single global variable) basis.

	 yylineno is not part of the POSIX specification.

     -	 The input() routine is not redefinable, though it may be called to
	 read characters following whatever has been matched by a rule.	 If
	 input() encounters an end-of-file, the normal yywrap() processing is
	 done.	A ``real'' end-of-file is returned by input() as EOF.

	 Input is instead controlled by defining the YY_INPUT macro.

	 The flex restriction that input() cannot be redefined is in
	 accordance with the POSIX specification, which simply does not
	 specify any way of controlling the scanner's input other than by
	 making an initial assignment to yyin.

     -	 The unput() routine is not redefinable.  This restriction is in
	 accordance with POSIX.

     -	 flex scanners are not as reentrant as lex scanners.  In particular,
	 if a scanner is interactive and an interrupt handler long-jumps out
	 of the scanner, and the scanner is subsequently called again, the
	 following error message may be displayed:

	       fatal flex scanner internal error--end of buffer missed

	 To reenter the scanner, first use

	       yyrestart(yyin);

	 Note that this call will throw away any buffered input; usually this
	 isn't a problem with an interactive scanner.

	 Also note that flex C++ scanner classes are reentrant, so if using
	 C++ is an option , they should be used instead.  See GENERATING C++
	 SCANNERS above for details.

     -	 output() is not supported.  Output from the ECHO macro is done to the
	 file-pointer yyout (default stdout).

	 output() is not part of the POSIX specification.

     -	 lex does not support exclusive start conditions (%x), though they are
	 in the POSIX specification.

     -	 When definitions are expanded, flex encloses them in parentheses.
	 With lex, the following:

	       NAME    [A-Z][A-Z0-9]*
	       %%
	       foo{NAME}?      printf("Found it\n");
	       %%

	 will not match the string "foo" because when the macro is expanded
	 the rule is equivalent to "foo[A-Z][A-Z0-9]*?" and the precedence is
	 such that the `?' is associated with "[A-Z0-9]*".  With flex, the
	 rule will be expanded to "foo([A-Z][A-Z0-9]*)?" and so the string
	 "foo" will match.

	 Note that if the definition begins with `^' or ends with `$' then it
	 is not expanded with parentheses, to allow these operators to appear
	 in definitions without losing their special meanings.	But the `<s>',
	 `/', and <<EOF>> operators cannot be used in a flex definition.

	 Using -l results in the lex behavior of no parentheses around the
	 definition.

	 The POSIX specification is that the definition be enclosed in
	 parentheses.

     -	 Some implementations of lex allow a rule's action to begin on a
	 separate line, if the rule's pattern has trailing whitespace:

	       %%
	       foo|bar<space here>
		 { foobar_action(); }

	 flex does not support this feature.

     -	 The lex `%r' (generate a Ratfor scanner) option is not supported.  It
	 is not part of the POSIX specification.

     -	 After a call to unput(), yytext is undefined until the next token is
	 matched, unless the scanner was built using ``%array''.  This is not
	 the case with lex or the POSIX specification.	The -l option does
	 away with this incompatibility.

     -	 The precedence of the `{}' (numeric range) operator is different.
	 lex interprets "abc{1,3}" as match one, two, or three occurrences of
	 `abc', whereas flex interprets it as match `ab' followed by one, two,
	 or three occurrences of `c'.  The latter is in agreement with the
	 POSIX specification.

     -	 The precedence of the `^' operator is different.  lex interprets
	 "^foo|bar" as match either `foo' at the beginning of a line, or `bar'
	 anywhere, whereas flex interprets it as match either `foo' or `bar'
	 if they come at the beginning of a line.  The latter is in agreement
	 with the POSIX specification.

     -	 The special table-size declarations such as `%a' supported by lex are
	 not required by flex scanners; flex ignores them.

     -	 The name FLEX_SCANNER is #define'd so scanners may be written for use
	 with either flex or lex.  Scanners also include YY_FLEX_MAJOR_VERSION
	 and YY_FLEX_MINOR_VERSION indicating which version of flex generated
	 the scanner (for example, for the 2.5 release, these defines would be
	 2 and 5, respectively).

     The following flex features are not included in lex or the POSIX
     specification:

	   C++ scanners
	   %option
	   start condition scopes
	   start condition stacks
	   interactive/non-interactive scanners
	   yy_scan_string() and friends
	   yyterminate()
	   yy_set_interactive()
	   yy_set_bol()
	   YY_AT_BOL()
	   <<EOF>>
	   <*>
	   YY_DECL
	   YY_START
	   YY_USER_ACTION
	   YY_USER_INIT
	   #line directives
	   %{}'s around actions
	   multiple actions on a line

     plus almost all of the flex flags.	 The last feature in the list refers
     to the fact that with flex Multiple actions ican be placed on the same
     line, separated with semi-colons, while with lex, the following

	   foo handle_foo(); ++num_foos_seen;

     is (rather surprisingly) truncated to

	   foo handle_foo();

     flex does not truncate the action.	 Actions that are not enclosed in
     braces are simply terminated at the end of the line.

FILES
     flex.skl		Skeleton scanner.  This file is only used when
			building flex, not when flex executes.

     lex.backup		Backing-up information for the -b flag (called lex.bck
			on some systems).

     lex.yy.c		Generated scanner (called lexyy.c on some systems).

     lex.yy.cc		Generated C++ scanner class, when using -+.

     <g++/FlexLexer.h>	Header file defining the C++ scanner base class,
			FlexLexer, and its derived class, yyFlexLexer.

     /usr/lib/libl.*	flex libraries.	 The /usr/lib/libfl.* libraries are
			links to these.	 Scanners must be linked using either
			-ll or -lfl.

EXIT STATUS
     The flex utility exits 0 on success, and >0 if an error occurs.

DIAGNOSTICS
     warning, rule cannot be matched  Indicates that the given rule cannot be
     matched because it follows other rules that will always match the same
     text as it.  For example, in the following ``foo'' cannot be matched
     because it comes after an identifier "catch-all" rule:

	   [a-z]+    got_identifier();
	   foo	     got_foo();

     Using REJECT in a scanner suppresses this warning.

     warning, -s option given but default rule can be matched  Means that it
     is possible (perhaps only in a particular start condition) that the
     default rule (match any single character) is the only one that will match
     a particular input.  Since -s was given, presumably this is not intended.

     reject_used_but_not_detected undefined
     yymore_used_but_not_detected undefined  These errors can occur at compile
     time.  They indicate that the scanner uses REJECT or yymore() but that
     flex failed to notice the fact, meaning that flex scanned the first two
     sections looking for occurrences of these actions and failed to find any,
     but somehow they snuck in (via an #include file, for example).  Use
     ``%option reject'' or ``%option yymore'' to indicate to flex that these
     features are really needed.

     flex scanner jammed  A scanner compiled with -s has encountered an input
     string which wasn't matched by any of its rules.  This error can also
     occur due to internal problems.

     token too large, exceeds YYLMAX  The scanner uses ``%array'' and one of
     its rules matched a string longer than the YYLMAX constant (8K bytes by
     default).	The value can be increased by #define'ing YYLMAX in the
     definitions section of flex input.

     scanner requires -8 flag to use the character 'x'	The scanner
     specification includes recognizing the 8-bit character `x' and the -8
     flag was not specified, and defaulted to 7-bit because the -Cf or -CF
     table compression options were used.  See the discussion of the -7 flag
     for details.

     flex scanner push-back overflow  unput() was used to push back so much
     text that the scanner's buffer could not hold both the pushed-back text
     and the current token in yytext.  Ideally the scanner should dynamically
     resize the buffer in this case, but at present it does not.

     input buffer overflow, can't enlarge buffer because scanner uses
     REJECT  The scanner was working on matching an extremely large token and
     needed to expand the input buffer.	 This doesn't work with scanners that
     use REJECT.

     fatal flex scanner internal error--end of buffer missed  This can occur
     in an scanner which is reentered after a long-jump has jumped out (or
     over) the scanner's activation frame.  Before reentering the scanner,
     use:

	   yyrestart(yyin);

     or, as noted above, switch to using the C++ scanner class.

     too many start conditions in <> construct!	 More start conditions than
     exist were listed in a <> construct (so at least one of them must have
     been listed twice).

SEE ALSO
     awk(1), sed(1), yacc(1)

     John Levine, Tony Mason, and Doug Brown, Lex & Yacc, O'Reilly and
     Associates, 2nd edition.

     Alfred Aho, Ravi Sethi, and Jeffrey Ullman, Compilers: Principles,
     Techniques and Tools, Addison-Wesley, 1986, Describes the
     pattern-matching techniques used by flex (deterministic finite automata).

STANDARDS
     The lex utility is compliant with the IEEE Std 1003.1-2008 (``POSIX'')
     specification, though its presence is optional.

     The flags [-78BbCcdFfhIiLloPpSsTVw+?], [--help], and [--version] are
     extensions to that specification.

AUTHORS
     Vern Paxson, with the help of many ideas and much inspiration from Van
     Jacobson.	Original version by Jef Poskanzer.  The fast table
     representation is a partial implementation of a design done by Van
     Jacobson.	The implementation was done by Kevin Gong and Vern Paxson.

     Thanks to the many flex beta-testers, feedbackers, and contributors,
     especially Francois Pinard, Casey Leedom, Robert Abramovitz, Stan
     Adermann, Terry Allen, David Barker-Plummer, John Basrai, Neal Becker,
     Nelson H.F. Beebe, benson@odi.com, Karl Berry, Peter A. Bigot, Simon
     Blanchard, Keith Bostic, Frederic Brehm, Ian Brockbank, Kin Cho, Nick
     Christopher, Brian Clapper, J.T. Conklin, Jason Coughlin, Bill Cox, Nick
     Cropper, Dave Curtis, Scott David Daniels, Chris G. Demetriou, Theo de
     Raadt, Mike Donahue, Chuck Doucette, Tom Epperly, Leo Eskin, Chris
     Faylor, Chris Flatters, Jon Forrest, Jeffrey Friedl, Joe Gayda, Kaveh R.
     Ghazi, Wolfgang Glunz, Eric Goldman, Christopher M. Gould, Ulrich Grepel,
     Peer Griebel, Jan Hajic, Charles Hemphill, NORO Hideo, Jarkko Hietaniemi,
     Scott Hofmann, Jeff Honig, Dana Hudes, Eric Hughes, John Interrante,
     Ceriel Jacobs, Michal Jaegermann, Sakari Jalovaara, Jeffrey R. Jones,
     Henry Juengst, Klaus Kaempf, Jonathan I. Kamens, Terrence O Kane, Amir
     Katz, ken@ken.hilco.com, Kevin B. Kenny, Steve Kirsch, Winfried Koenig,
     Marq Kole, Ronald Lamprecht, Greg Lee, Rohan Lenard, Craig Leres, John
     Levine, Steve Liddle, David Loffredo, Mike Long, Mohamed el Lozy, Brian
     Madsen, Malte, Joe Marshall, Bengt Martensson, Chris Metcalf, Luke
     Mewburn, Jim Meyering, R. Alexander Milowski, Erik Naggum, G.T. Nicol,
     Landon Noll, James Nordby, Marc Nozell, Richard Ohnemus, Karsten Pahnke,
     Sven Panne, Roland Pesch, Walter Pelissero, Gaumond Pierre, Esmond Pitt,
     Jef Poskanzer, Joe Rahmeh, Jarmo Raiha, Frederic Raimbault, Pat Rankin,
     Rick Richardson, Kevin Rodgers, Kai Uwe Rommel, Jim Roskind, Alberto
     Santini, Andreas Scherer, Darrell Schiebel, Raf Schietekat, Doug Schmidt,
     Philippe Schnoebelen, Andreas Schwab, Larry Schwimmer, Alex Siegel,
     Eckehard Stolz, Jan-Erik Strvmquist, Mike Stump, Paul Stuart, Dave
     Tallman, Ian Lance Taylor, Chris Thewalt, Richard M. Timoney, Jodi Tsai,
     Paul Tuinenga, Gary Weik, Frank Whaley, Gerhard Wilhelms, Kent Williams,
     Ken Yap, Ron Zellar, Nathan Zelle, David Zuhn, and those whose names have
     slipped my marginal mail-archiving skills but whose contributions are
     appreciated all the same.

     Thanks to Keith Bostic, Jon Forrest, Noah Friedman, John Gilmore, Craig
     Leres, John Levine, Bob Mulcahy, G.T.  Nicol, Francois Pinard, Rich Salz,
     and Richard Stallman for help with various distribution headaches.

     Thanks to Esmond Pitt and Earle Horton for 8-bit character support; to
     Benson Margulies and Fred Burke for C++ support; to Kent Williams and Tom
     Epperly for C++ class support; to Ove Ewerlid for support of NUL's; and
     to Eric Hughes for support of multiple buffers.

     This work was primarily done when I was with the Real Time Systems Group
     at the Lawrence Berkeley Laboratory in Berkeley, CA.  Many thanks to all
     there for the support I received.

     Send comments to <vern@ee.lbl.gov>.

BUGS
     Some trailing context patterns cannot be properly matched and generate
     warning messages (dangerous trailing context).  These are patterns where
     the ending of the first part of the rule matches the beginning of the
     second part, such as "zx*/xy*", where the `x*' matches the `x' at the
     beginning of the trailing context.	 (Note that the POSIX draft states
     that the text matched by such patterns is undefined.)

     For some trailing context rules, parts which are actually fixed-length
     are not recognized as such, leading to the above mentioned performance
     loss.  In particular, parts using `|' or `{n}' (such as "foo{3}") are
     always considered variable-length.

     Combining trailing context with the special `|' action can result in
     fixed trailing context being turned into the more expensive variable
     trailing context.	For example, in the following:

	   %%
	   abc	    |
	   xyz/def

     Use of unput() invalidates yytext and yyleng, unless the ``%array''
     directive or the -l option has been used.

     Pattern-matching of NUL's is substantially slower than matching other
     characters.

     Dynamic resizing of the input buffer is slow, as it entails rescanning
     all the text matched so far by the current (generally huge) token.

     Due to both buffering of input and read-ahead, it is not possible to
     intermix calls to <stdio.h> routines, such as, for example, getchar(),
     with flex rules and expect it to work.  Call input() instead.

     The total table entries listed by the -v flag excludes the number of
     table entries needed to determine what rule has been matched.  The number
     of entries is equal to the number of DFA states if the scanner does not
     use REJECT, and somewhat greater than the number of states if it does.

     REJECT cannot be used with the -f or -F options.

     The flex internal algorithms need documentation.

OpenBSD 4.9		       October 18, 2010			   OpenBSD 4.9
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