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GFORTRAN(1)			      GNU			   GFORTRAN(1)

NAME
       gfortran - GNU Fortran compiler

SYNOPSIS
       gfortran [-c|-S|-E]
		[-g] [-pg] [-Olevel]
		[-Wwarn...] [-pedantic]
		[-Idir...] [-Ldir...]
		[-Dmacro[=defn]...] [-Umacro]
		[-foption...]	     [-mmachine-option...]
		[-o outfile] infile...

       Only the most useful options are listed here; see below for the
       remainder.

DESCRIPTION
       The gfortran command supports all the options supported by the gcc
       command.	 Only options specific to GNU Fortran are documented here.

       All GCC and GNU Fortran options are accepted both by gfortran and by
       gcc (as well as any other drivers built at the same time, such as g++),
       since adding GNU Fortran to the GCC distribution enables acceptance of
       GNU Fortran options by all of the relevant drivers.

       In some cases, options have positive and negative forms; the negative
       form of -ffoo would be -fno-foo.	 This manual documents only one of
       these two forms, whichever one is not the default.

OPTIONS
       Here is a summary of all the options specific to GNU Fortran, grouped
       by type.	 Explanations are in the following sections.

       Fortran Language Options
	   -fall-intrinsics  -ffree-form  -fno-fixed-form -fdollar-ok
	   -fimplicit-none  -fmax-identifier-length -std=std -fd-lines-as-code
	   -fd-lines-as-comments -ffixed-line-length-n
	   -ffixed-line-length-none -ffree-line-length-n
	   -ffree-line-length-none -fdefault-double-8  -fdefault-integer-8
	   -fdefault-real-8 -fcray-pointer  -fopenmp  -frange-check
	   -fno-backslash

       Error and Warning Options
	   -fmax-errors=n -fsyntax-only	 -pedantic  -pedantic-errors -w	 -Wall
	   -Waliasing  -Wampersand  -Wcharacter-truncation  -Wconversion
	   -Wimplicit-interface	 -Wline-truncation  -Wnonstd-intrinsics
	   -Wsurprising -Wno-tabs  -Wunderflow	-W

       Debugging Options
	   -fdump-parse-tree  -ffpe-trap=list

       Directory Options
	   -Idir  -Jdir	 -Mdir

       Runtime Options
	   -fconvert=conversion	 -frecord-marker=length
	   -fmax-subrecord-length=length

       Code Generation Options
	   -fno-automatic  -ff2c  -fno-underscoring -fsecond-underscore
	   -fbounds-check  -fmax-stack-var-size=n -fpack-derived
	   -frepack-arrays  -fshort-enums

   Options Controlling Fortran Dialect
       The following options control the details of the Fortran dialect
       accepted by the compiler:

       -ffree-form

       -ffixed-form
	   Specify the layout used by the source file.	The free form layout
	   was introduced in Fortran 90.  Fixed form was traditionally used in
	   older Fortran programs.  When neither option is specified, the
	   source form is determined by the file extension.

       -fall-intrinsics
	   Accept all of the intrinsic procedures provided in libgfortran
	   without regard to the setting of -std.  In particular, this option
	   can be quite useful with -std=f95.  Additionally, gfortran will
	   ignore -Wnonstd-intrinsics.

       -fd-lines-as-code

       -fd-lines-as-comments
	   Enable special treatment for lines beginning with "d" or "D" in
	   fixed form sources.	If the -fd-lines-as-code option is given they
	   are treated as if the first column contained a blank.  If the
	   -fd-lines-as-comments option is given, they are treated as comment
	   lines.

       -fdefault-double-8
	   Set the "DOUBLE PRECISION" type to an 8 byte wide type.

       -fdefault-integer-8
	   Set the default integer and logical types to an 8 byte wide type.
	   Do nothing if this is already the default.

       -fdefault-real-8
	   Set the default real type to an 8 byte wide type.  Do nothing if
	   this is already the default.

       -fdollar-ok
	   Allow $ as a valid character in a symbol name.

       -fno-backslash
	   Change the interpretation of backslashes in string literals from
	   "C-style" escape characters to a single backslash character.

       -ffixed-line-length-n
	   Set column after which characters are ignored in typical fixed-form
	   lines in the source file, and through which spaces are assumed (as
	   if padded to that length) after the ends of short fixed-form lines.

	   Popular values for n include 72 (the standard and the default), 80
	   (card image), and 132 (corresponding to "extended-source" options
	   in some popular compilers).	n may also be none, meaning that the
	   entire line is meaningful and that continued character constants
	   never have implicit spaces appended to them to fill out the line.
	   -ffixed-line-length-0 means the same thing as
	   -ffixed-line-length-none.

       -ffree-line-length-n
	   Set column after which characters are ignored in typical free-form
	   lines in the source file. The default value is 132.	n may be none,
	   meaning that the entire line is meaningful.	-ffree-line-length-0
	   means the same thing as -ffree-line-length-none.

       -fmax-identifier-length=n
	   Specify the maximum allowed identifier length. Typical values are
	   31 (Fortran 95) and 63 (Fortran 2003).

       -fimplicit-none
	   Specify that no implicit typing is allowed, unless overridden by
	   explicit "IMPLICIT" statements.  This is the equivalent of adding
	   "implicit none" to the start of every procedure.

       -fcray-pointer
	   Enable the Cray pointer extension, which provides C-like pointer
	   functionality.

       -fopenmp
	   Enable the OpenMP extensions.  This includes OpenMP "!$omp"
	   directives in free form and "c$omp", *$omp and "!$omp" directives
	   in fixed form, "!$" conditional compilation sentinels in free form
	   and "c$", "*$" and "!$" sentinels in fixed form, and when linking
	   arranges for the OpenMP runtime library to be linked in.

       -frange-check
	   Enable range checking on results of simplification of constant
	   expressions during compilation.  For example, by default, GNU
	   Fortran will give an overflow error at compile time when
	   simplifying "a = EXP(1000)". With -fno-range-check, no error will
	   be given and the variable "a" will be assigned the value
	   "+Infinity".	 Similarly, "DATA i/Z'FFFFFFFF'/" will result in an
	   integer overflow on most systems, but with -fno-range-check the
	   value will "wrap around" and "i" will be initialized to -1 instead.

       -std=std
	   Specify the standard to which the program is expected to conform,
	   which may be one of f95, f2003, gnu, or legacy.  The default value
	   for std is gnu, which specifies a superset of the Fortran 95
	   standard that includes all of the extensions supported by GNU
	   Fortran, although warnings will be given for obsolete extensions
	   not recommended for use in new code.	 The legacy value is
	   equivalent but without the warnings for obsolete extensions, and
	   may be useful for old non-standard programs.	 The f95 and f2003
	   values specify strict conformance to the Fortran 95 and Fortran
	   2003 standards, respectively; errors are given for all extensions
	   beyond the relevant language standard, and warnings are given for
	   the Fortran 77 features that are permitted but obsolescent in later
	   standards.

   Options to Request or Suppress Errors and Warnings
       Errors are diagnostic messages that report that the GNU Fortran
       compiler cannot compile the relevant piece of source code.  The
       compiler will continue to process the program in an attempt to report
       further errors to aid in debugging, but will not produce any compiled
       output.

       Warnings are diagnostic messages that report constructions which are
       not inherently erroneous but which are risky or suggest there is likely
       to be a bug in the program.  Unless -Werror is specified, they do not
       prevent compilation of the program.

       You can request many specific warnings with options beginning -W, for
       example -Wimplicit to request warnings on implicit declarations.	 Each
       of these specific warning options also has a negative form beginning
       -Wno- to turn off warnings; for example, -Wno-implicit.	This manual
       lists only one of the two forms, whichever is not the default.

       These options control the amount and kinds of errors and warnings
       produced by GNU Fortran:

       -fmax-errors-n
	   Limits the maximum number of error messages to n, at which point
	   GNU Fortran bails out rather than attempting to continue processing
	   the source code.  If n is 0, there is no limit on the number of
	   error messages produced.

       -fsyntax-only
	   Check the code for syntax errors, but don't do anything beyond
	   that.

       -pedantic
	   Issue warnings for uses of extensions to Fortran 95.	 -pedantic
	   also applies to C-language constructs where they occur in GNU
	   Fortran source files, such as use of \e in a character constant
	   within a directive like "#include".

	   Valid Fortran 95 programs should compile properly with or without
	   this option.	 However, without this option, certain GNU extensions
	   and traditional Fortran features are supported as well.  With this
	   option, many of them are rejected.

	   Some users try to use -pedantic to check programs for conformance.
	   They soon find that it does not do quite what they want---it finds
	   some nonstandard practices, but not all.  However, improvements to
	   GNU Fortran in this area are welcome.

	   This should be used in conjunction with -std=f95 or -std=f2003.

       -pedantic-errors
	   Like -pedantic, except that errors are produced rather than
	   warnings.

       -w  Inhibit all warning messages.

       -Wall
	   Enables commonly used warning options pertaining to usage that we
	   recommend avoiding and that we believe are easy to avoid.  This
	   currently includes -Waliasing, -Wampersand, -Wsurprising,
	   -Wnonstd-intrinsics, -Wno-tabs, and -Wline-truncation.

       -Waliasing
	   Warn about possible aliasing of dummy arguments. Specifically, it
	   warns if the same actual argument is associated with a dummy
	   argument with "INTENT(IN)" and a dummy argument with "INTENT(OUT)"
	   in a call with an explicit interface.

	   The following example will trigger the warning.

		     interface
		       subroutine bar(a,b)
			 integer, intent(in) :: a
			 integer, intent(out) :: b
		       end subroutine
		     end interface
		     integer :: a

		     call bar(a,a)

       -Wampersand
	   Warn about missing ampersand in continued character constants. The
	   warning is given with -Wampersand, -pedantic, -std=f95, and
	   -std=f2003. Note: With no ampersand given in a continued character
	   constant, GNU Fortran assumes continuation at the first
	   non-comment, non-whitespace character after the ampersand that
	   initiated the continuation.

       -Wcharacter-truncation
	   Warn when a character assignment will truncate the assigned string.

       -Wconversion
	   Warn about implicit conversions between different types.

       -Wimplicit-interface
	   Warn if a procedure is called without an explicit interface.	 Note
	   this only checks that an explicit interface is present.  It does
	   not check that the declared interfaces are consistent across
	   program units.

       -Wnonstd-intrinsics
	   Warn if the user tries to use an intrinsic that does not belong to
	   the standard the user has chosen via the -std option.

       -Wsurprising
	   Produce a warning when "suspicious" code constructs are
	   encountered.	 While technically legal these usually indicate that
	   an error has been made.

	   This currently produces a warning under the following
	   circumstances:
	   o   An INTEGER SELECT construct has a CASE that can never be
	       matched as its lower value is greater than its upper value.

	   o   A LOGICAL SELECT construct has three CASE statements.

       -Wtabs
	   By default, tabs are accepted as whitespace, but tabs are not
	   members of the Fortran Character Set.  -Wno-tabs will cause a
	   warning to be issued if a tab is encountered. Note, -Wno-tabs is
	   active for -pedantic, -std=f95, -std=f2003, and -Wall.

       -Wunderflow
	   Produce a warning when numerical constant expressions are
	   encountered, which yield an UNDERFLOW during compilation.

       -Werror
	   Turns all warnings into errors.

       -W  Turns on "extra warnings" and, if optimization is specified via -O,
	   the -Wuninitialized option.	(This might change in future versions
	   of GNU Fortran.)

       Some of these have no effect when compiling programs written in
       Fortran.

   Options for Debugging Your Program or GNU Fortran
       GNU Fortran has various special options that are used for debugging
       either your program or the GNU Fortran compiler.

       -fdump-parse-tree
	   Output the internal parse tree before starting code generation.
	   Only really useful for debugging the GNU Fortran compiler itself.

       -ffpe-trap=list
	   Specify a list of IEEE exceptions when a Floating Point Exception
	   (FPE) should be raised.  On most systems, this will result in a
	   SIGFPE signal being sent and the program being interrupted,
	   producing a core file useful for debugging.	list is a (possibly
	   empty) comma-separated list of the following IEEE exceptions:
	   invalid (invalid floating point operation, such as "SQRT(-1.0)"),
	   zero (division by zero), overflow (overflow in a floating point
	   operation), underflow (underflow in a floating point operation),
	   precision (loss of precision during operation) and denormal
	   (operation produced a denormal value).

   Options for Directory Search
       These options affect how GNU Fortran searches for files specified by
       the "INCLUDE" directive and where it searches for previously compiled
       modules.

       It also affects the search paths used by cpp when used to preprocess
       Fortran source.

       -Idir
	   These affect interpretation of the "INCLUDE" directive (as well as
	   of the "#include" directive of the cpp preprocessor).

	   Also note that the general behavior of -I and "INCLUDE" is pretty
	   much the same as of -I with "#include" in the cpp preprocessor,
	   with regard to looking for header.gcc files and other such things.

	   This path is also used to search for .mod files when previously
	   compiled modules are required by a "USE" statement.

       -Mdir

       -Jdir
	   This option specifies where to put .mod files for compiled modules.
	   It is also added to the list of directories to searched by an "USE"
	   statement.

	   The default is the current directory.

	   -J is an alias for -M to avoid conflicts with existing GCC options.

   Influencing runtime behavior
       These options affect the runtime behavior of programs compiled with GNU
       Fortran.

       -fconvert=conversion
	   Specify the representation of data for unformatted files.  Valid
	   values for conversion are: native, the default; swap, swap between
	   big- and little-endian; big-endian, use big-endian representation
	   for unformatted files; little-endian, use little-endian
	   representation for unformatted files.

	   This option has an effect only when used in the main program.  The
	   "CONVERT" specifier and the GFORTRAN_CONVERT_UNIT environment
	   variable override the default specified by -fconvert.

       -frecord-marker=length
	   Specify the length of record markers for unformatted files.	Valid
	   values for length are 4 and 8.  Default is 4.  This is different
	   from previous versions of gfortran, which specified a default
	   record marker length of 8 on most systems.  If you want to read or
	   write files compatible with earlier versions of gfortran, use
	   -frecord-marker=8.

       -fmax-subrecord-length=length
	   Specify the maximum length for a subrecord.	The maximum permitted
	   value for length is 2147483639, which is also the default.  Only
	   really useful for use by the gfortran testsuite.

   Options for Code Generation Conventions
       These machine-independent options control the interface conventions
       used in code generation.

       Most of them have both positive and negative forms; the negative form
       of -ffoo would be -fno-foo.  In the table below, only one of the forms
       is listed---the one which is not the default.  You can figure out the
       other form by either removing no- or adding it.

       -fno-automatic
	   Treat each program unit as if the "SAVE" statement was specified
	   for every local variable and array referenced in it. Does not
	   affect common blocks. (Some Fortran compilers provide this option
	   under the name -static.)

       -ff2c
	   Generate code designed to be compatible with code generated by g77
	   and f2c.

	   The calling conventions used by g77 (originally implemented in f2c)
	   require functions that return type default "REAL" to actually
	   return the C type "double", and functions that return type
	   "COMPLEX" to return the values via an extra argument in the calling
	   sequence that points to where to store the return value.  Under the
	   default GNU calling conventions, such functions simply return their
	   results as they would in GNU C---default "REAL" functions return
	   the C type "float", and "COMPLEX" functions return the GNU C type
	   "complex".  Additionally, this option implies the
	   -fsecond-underscore option, unless -fno-second-underscore is
	   explicitly requested.

	   This does not affect the generation of code that interfaces with
	   the libgfortran library.

	   Caution: It is not a good idea to mix Fortran code compiled with
	   -ff2c with code compiled with the default -fno-f2c calling
	   conventions as, calling "COMPLEX" or default "REAL" functions
	   between program parts which were compiled with different calling
	   conventions will break at execution time.

	   Caution: This will break code which passes intrinsic functions of
	   type default "REAL" or "COMPLEX" as actual arguments, as the
	   library implementations use the -fno-f2c calling conventions.

       -fno-underscoring
	   Do not transform names of entities specified in the Fortran source
	   file by appending underscores to them.

	   With -funderscoring in effect, GNU Fortran appends one underscore
	   to external names with no underscores.  This is done to ensure
	   compatibility with code produced by many UNIX Fortran compilers.

	   Caution: The default behavior of GNU Fortran is incompatible with
	   f2c and g77, please use the -ff2c option if you want object files
	   compiled with GNU Fortran to be compatible with object code created
	   with these tools.

	   Use of -fno-underscoring is not recommended unless you are
	   experimenting with issues such as integration of GNU Fortran into
	   existing system environments (vis-a-vis existing libraries, tools,
	   and so on).

	   For example, with -funderscoring, and assuming other defaults like
	   -fcase-lower and that "j()" and "max_count()" are external
	   functions while "my_var" and "lvar" are local variables, a
	   statement like

		   I = J() + MAX_COUNT (MY_VAR, LVAR)

	   is implemented as something akin to:

		   i = j_() + max_count__(&my_var__, &lvar);

	   With -fno-underscoring, the same statement is implemented as:

		   i = j() + max_count(&my_var, &lvar);

	   Use of -fno-underscoring allows direct specification of
	   user-defined names while debugging and when interfacing GNU Fortran
	   code with other languages.

	   Note that just because the names match does not mean that the
	   interface implemented by GNU Fortran for an external name matches
	   the interface implemented by some other language for that same
	   name.  That is, getting code produced by GNU Fortran to link to
	   code produced by some other compiler using this or any other method
	   can be only a small part of the overall solution---getting the code
	   generated by both compilers to agree on issues other than naming
	   can require significant effort, and, unlike naming disagreements,
	   linkers normally cannot detect disagreements in these other areas.

	   Also, note that with -fno-underscoring, the lack of appended
	   underscores introduces the very real possibility that a
	   user-defined external name will conflict with a name in a system
	   library, which could make finding unresolved-reference bugs quite
	   difficult in some cases---they might occur at program run time, and
	   show up only as buggy behavior at run time.

	   In future versions of GNU Fortran we hope to improve naming and
	   linking issues so that debugging always involves using the names as
	   they appear in the source, even if the names as seen by the linker
	   are mangled to prevent accidental linking between procedures with
	   incompatible interfaces.

       -fsecond-underscore
	   By default, GNU Fortran appends an underscore to external names.
	   If this option is used GNU Fortran appends two underscores to names
	   with underscores and one underscore to external names with no
	   underscores.	 GNU Fortran also appends two underscores to internal
	   names with underscores to avoid naming collisions with external
	   names.

	   This option has no effect if -fno-underscoring is in effect.	 It is
	   implied by the -ff2c option.

	   Otherwise, with this option, an external name such as "MAX_COUNT"
	   is implemented as a reference to the link-time external symbol
	   "max_count__", instead of "max_count_".  This is required for
	   compatibility with g77 and f2c, and is implied by use of the -ff2c
	   option.

       -fbounds-check
	   Enable generation of run-time checks for array subscripts and
	   against the declared minimum and maximum values.  It also checks
	   array indices for assumed and deferred shape arrays against the
	   actual allocated bounds.

	   In the future this may also include other forms of checking, e.g.,
	   checking substring references.

       -fmax-stack-var-size=n
	   This option specifies the size in bytes of the largest array that
	   will be put on the stack.

	   This option currently only affects local arrays declared with
	   constant bounds, and may not apply to all character variables.
	   Future versions of GNU Fortran may improve this behavior.

	   The default value for n is 32768.

       -fpack-derived
	   This option tells GNU Fortran to pack derived type members as
	   closely as possible.	 Code compiled with this option is likely to
	   be incompatible with code compiled without this option, and may
	   execute slower.

       -frepack-arrays
	   In some circumstances GNU Fortran may pass assumed shape array
	   sections via a descriptor describing a noncontiguous area of
	   memory.  This option adds code to the function prologue to repack
	   the data into a contiguous block at runtime.

	   This should result in faster accesses to the array.	However it can
	   introduce significant overhead to the function call, especially
	   when the passed data is noncontiguous.

       -fshort-enums
	   This option is provided for interoperability with C code that was
	   compiled with the -fshort-enums option.  It will make GNU Fortran
	   choose the smallest "INTEGER" kind a given enumerator set will fit
	   in, and give all its enumerators this kind.

ENVIRONMENT
       The gfortran compiler currently does not make use of any environment
       variables to control its operation above and beyond those that affect
       the operation of gcc.

BUGS
       For instructions on reporting bugs, see <http://gcc.gnu.org/bugs.html>.

SEE ALSO
       gpl(7), gfdl(7), fsf-funding(7), cpp(1), gcov(1), gcc(1), as(1), ld(1),
       gdb(1), adb(1), dbx(1), sdb(1) and the Info entries for gcc, cpp,
       gfortran, as, ld, binutils and gdb.

AUTHOR
       See the Info entry for gfortran for contributors to GCC and GNU
       Fortran.

COPYRIGHT
       Copyright (c) 2004, 2005, 2006, 2007 Free Software Foundation, Inc.

       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.2 or
       any later version published by the Free Software Foundation; with the
       Invariant Sections being "GNU General Public License" and "Funding Free
       Software", the Front-Cover texts being (a) (see below), and with the
       Back-Cover Texts being (b) (see below).	A copy of the license is
       included in the gfdl(7) man page.

       (a) The FSF's Front-Cover Text is:

	    A GNU Manual

       (b) The FSF's Back-Cover Text is:

	    You have freedom to copy and modify this GNU Manual, like GNU
	    software.  Copies published by the Free Software Foundation raise
	    funds for GNU development.

gcc-4.2.1						     February 17, 2011
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