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GFORTRAN(1)			      GNU			   GFORTRAN(1)

NAME
       gfortran - GNU Fortran 95 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 gfortran are documented here.

       All gcc and gfortran 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 gfortran to the gcc distribution enables acceptance of
       gfortran 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
	   -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  -frange-check

       Warning Options
	   -fsyntax-only  -pedantic  -pedantic-errors -w  -Wall	 -Waliasing
	   -Wampersand -Wconversion -Wimplicit-interface -Wnonstd-intrinsics
	   -Wsurprising -Wunderflow -Wunused-labels -Wline-truncation -W

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

       Directory Options
	   -Idir  -Mdir

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

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

       Options Controlling Fortran Dialect

       The following options control the dialect of Fortran that the compiler
       accepts:

       -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.

       -fd-lines-as-code
       -fd-lines-as-comment
	   Enables special treating for lines 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.

       -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
	   Compile switch to change the interpretation of a backslash 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 (corresponds to "extended-source" options in
	   some popular compilers).  n may 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. For free-form, 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 200x).

       -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
	   Enables the Cray pointer extension, which provides a C-like
	   pointer.

       -frange-check
	   Enable range checking on results of simplification of constant
	   expressions during compilation.  For example, by default, gfortran
	   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".

       -std=std
	   Conform to the specified standard.  Allowed values for std are gnu,
	   f95, f2003 and legacy.

       Options to Request or Suppress Warnings

       Warnings are diagnostic messages that report constructions which are
       not inherently erroneous but which are risky or suggest there might
       have been an error.

       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 warnings produced by GNU
       Fortran:

       -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
	   gfortran in this area are welcome.

	   This should be used in conjunction with -std=std.

       -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 -Wunused-labels, -Waliasing, -Wampersand,
	   -Wsurprising, -Wnonstd-intrinsic, 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 literals. The
	   warning is given with -Wampersand, -pedantic, and -std=f95.	Note:
	   With no ampersand given in a continued character literal, gfortran
	   assumes continuation at the first non-comment, non-whitespace
	   character.

       -Wconversion
	   Warn about implicit conversions between different types.

       -Wimplicit-interface
	   Warn about when procedure are 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-intrinsic
	   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:

	   ·   An INTEGER SELECT construct has a CASE that can never be
	       matched as its lower value is greater than its upper value.

	   ·   A LOGICAL SELECT construct has three CASE statements.

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

       -Wunused-labels
	   Warn whenever a label is defined but never referenced.

       -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 gfortran

       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 gfortran

       -fdump-parse-tree
	   Output the internal parse tree before starting code generation.
	   Only really useful for debugging gfortran 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 denormal value).

       Options for Directory Search

       These options affect how gfortran 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 gfortran.

       -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 whatever "off_t" is
	   specified to be on that particular system.  Note that specifying
	   length as 4 limits the record length of unformatted files to 2 GB.
	   This option does not extend the maximum possible record length on
	   systems where "off_t" is a four_byte quantity.

       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, gfortran 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 gfortran is incompatible with f2c
	   and g77, please use the -ff2c option if you want object files
	   compiled with gfortran 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 gfortran code
	   with other languages.

	   Note that just because the names match does not mean that the
	   interface implemented by gfortran for an external name matches the
	   interface implemented by some other language for that same name.
	   That is, getting code produced by gfortran 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 gfortran 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, gfortran appends an underscore to external names.  If
	   this option is used gfortran appends two underscores to names with
	   underscores and one underscore to external names with no
	   underscores.	 (gfortran 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, eg.
	   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 gfortran may improve this behavior.

	   The default value for n is 32768.

       -fpackderived
	   This option tells gfortran 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 gfortran may pass assumed shape array
	   sections via a descriptor describing a discontiguous 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 discontiguous.

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

ENVIRONMENT
       GNU Fortran 95 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 GFORTRAN.

COPYRIGHT
       Copyright (c) 2004, 2005 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-4.1.2			  2010-05-25			   GFORTRAN(1)
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