mirror of git://gcc.gnu.org/git/gcc.git
934 lines
35 KiB
Plaintext
934 lines
35 KiB
Plaintext
@c Copyright (C) 2004, 2005, 2006, 2007
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@c Free Software Foundation, Inc.
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@c This is part of the GNU Fortran manual.
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@c For copying conditions, see the file gfortran.texi.
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@ignore
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@c man begin COPYRIGHT
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Copyright @copyright{} 2004, 2005, 2006, 2007
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Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.2 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being ``GNU General Public License'' and ``Funding
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Free Software'', the Front-Cover texts being (a) (see below), and with
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the Back-Cover Texts being (b) (see below). A copy of the license is
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included in the gfdl(7) man page.
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development.
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@c man end
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@c Set file name and title for the man page.
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@setfilename gfortran
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@settitle GNU Fortran compiler.
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@c man begin SYNOPSIS
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gfortran [@option{-c}|@option{-S}|@option{-E}]
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[@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
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[@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
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[@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
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[@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
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[@option{-f}@var{option}@dots{}]
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[@option{-m}@var{machine-option}@dots{}]
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[@option{-o} @var{outfile}] @var{infile}@dots{}
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Only the most useful options are listed here; see below for the
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remainder.
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@c man end
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@c man begin SEEALSO
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gpl(7), gfdl(7), fsf-funding(7),
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cpp(1), gcov(1), gcc(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
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and the Info entries for @file{gcc}, @file{cpp}, @file{gfortran}, @file{as},
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@file{ld}, @file{binutils} and @file{gdb}.
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@c man end
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@c man begin BUGS
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For instructions on reporting bugs, see
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@w{@uref{http://gcc.gnu.org/bugs.html}}.
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@c man end
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@c man begin AUTHOR
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See the Info entry for @command{gfortran} for contributors to GCC and
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GNU Fortran.
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@c man end
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@end ignore
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@node Invoking GNU Fortran
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@chapter GNU Fortran Command Options
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@cindex GNU Fortran command options
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@cindex command options
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@cindex options, @command{gfortran} command
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@c man begin DESCRIPTION
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The @command{gfortran} command supports all the options supported by the
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@command{gcc} command. Only options specific to GNU Fortran are documented here.
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@xref{Invoking GCC,,GCC Command Options,gcc,Using the GNU Compiler
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Collection (GCC)}, for information
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on the non-Fortran-specific aspects of the @command{gcc} command (and,
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therefore, the @command{gfortran} command).
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@cindex options, negative forms
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@cindex negative forms of options
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All GCC and GNU Fortran options
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are accepted both by @command{gfortran} and by @command{gcc}
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(as well as any other drivers built at the same time,
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such as @command{g++}),
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since adding GNU Fortran to the GCC distribution
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enables acceptance of GNU Fortran options
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by all of the relevant drivers.
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In some cases, options have positive and negative forms;
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the negative form of @option{-ffoo} would be @option{-fno-foo}.
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This manual documents only one of these two forms, whichever
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one is not the default.
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@c man end
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@menu
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* Option Summary:: Brief list of all @command{gfortran} options,
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without explanations.
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* Fortran Dialect Options:: Controlling the variant of Fortran language
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compiled.
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* Error and Warning Options:: How picky should the compiler be?
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* Debugging Options:: Symbol tables, measurements, and debugging dumps.
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* Directory Options:: Where to find module files
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* Runtime Options:: Influencing runtime behavior
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* Code Gen Options:: Specifying conventions for function calls, data layout
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and register usage.
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* Environment Variables:: Env vars that affect @command{gfortran}.
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@end menu
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@node Option Summary
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@section Option Summary
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@c man begin OPTIONS
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Here is a summary of all the options specific to GNU Fortran, grouped
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by type. Explanations are in the following sections.
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@table @emph
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@item Fortran Language Options
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@xref{Fortran Dialect Options,,Options Controlling Fortran Dialect}.
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@gccoptlist{-fall-intrinsics -ffree-form -fno-fixed-form @gol
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-fdollar-ok -fimplicit-none -fmax-identifier-length @gol
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-std=@var{std} -fd-lines-as-code -fd-lines-as-comments @gol
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-ffixed-line-length-@var{n} -ffixed-line-length-none @gol
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-ffree-line-length-@var{n} -ffree-line-length-none @gol
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-fdefault-double-8 -fdefault-integer-8 -fdefault-real-8 @gol
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-fcray-pointer -fopenmp -frange-check -fno-backslash }
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@item Error and Warning Options
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@xref{Error and Warning Options,,Options to Request or Suppress Errors
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and Warnings}.
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@gccoptlist{-fmax-errors=@var{n} @gol
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-fsyntax-only -pedantic -pedantic-errors @gol
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-w -Wall -Waliasing -Wampersand -Wconversion -Wimplicit-interface @gol
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-Wtabs -Wnonstd-intrinsics -Wsurprising -Wunderflow @gol
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-Wline-truncation -W}
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@item Debugging Options
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@xref{Debugging Options,,Options for Debugging Your Program or GCC}.
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@gccoptlist{-fdump-parse-tree -ffpe-trap=@var{list}
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-fdump-core}
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@item Directory Options
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@xref{Directory Options,,Options for Directory Search}.
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@gccoptlist{-I@var{dir} -M@var{dir}}
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@item Runtime Options
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@xref{Runtime Options,,Options for influencing runtime behavior}.
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@gccoptlist{-fconvert=@var{conversion} -frecord-marker=@var{length}}
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@item Code Generation Options
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@xref{Code Gen Options,,Options for Code Generation Conventions}.
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@gccoptlist{-fno-automatic -ff2c -fno-underscoring
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-fsecond-underscore @gol
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-fbounds-check -fmax-stack-var-size=@var{n} @gol
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-fpack-derived -frepack-arrays -fshort-enums -fexternal-blas @gol
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-fblas-matmul-limit=@var{n}}
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@end table
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@menu
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* Fortran Dialect Options:: Controlling the variant of Fortran language
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compiled.
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* Error and Warning Options:: How picky should the compiler be?
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* Debugging Options:: Symbol tables, measurements, and debugging dumps.
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* Directory Options:: Where to find module files
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* Runtime Options:: Influencing runtime behavior
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* Code Gen Options:: Specifying conventions for function calls, data layout
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and register usage.
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@end menu
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@node Fortran Dialect Options
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@section Options Controlling Fortran Dialect
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@cindex dialect options
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@cindex language, dialect options
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@cindex options, dialect
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The following options control the details of the Fortran dialect
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accepted by the compiler:
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@table @gcctabopt
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@item -ffree-form
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@item -ffixed-form
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@cindex @code{-ffree-form} option
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@cindex option, @code{-ffree-form}
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@cindex @code{-fno-fixed-form} option
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@cindex option, @code{-fno-fixed-form}
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@cindex source file format
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@cindex free form
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@cindex fixed form
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@cindex Source Form
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@cindex Fortran 90, features
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Specify the layout used by the source file. The free form layout
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was introduced in Fortran 90. Fixed form was traditionally used in
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older Fortran programs. When neither option is specified, the source
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form is determined by the file extension.
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@item -fall-intrinsics
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@cindex @code{-fall-intrinsics} option
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@cindex option, @code{-fall-intrinsics}
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Accept all of the intrinsic procedures provided in libgfortran
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without regard to the setting of @option{-std}. In particular,
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this option can be quite useful with @option{-std=f95}. Additionally,
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@command{gfortran} will ignore @option{-Wnonstd-intrinsics}.
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@item -fd-lines-as-code
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@item -fd-lines-as-comment
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@cindex @code{-fd-lines-as-code}, option
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@cindex option, @code{-fd-lines-as-code}
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@cindex @code{-fd-lines-as-comments}, option
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@cindex option, @code{-fd-lines-as-comments}
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Enable special treatment for lines beginning with @code{d} or @code{D}
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in fixed form sources. If the @option{-fd-lines-as-code} option is
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given they are treated as if the first column contained a blank. If the
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@option{-fd-lines-as-comments} option is given, they are treated as
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comment lines.
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@item -fdefault-double-8
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@cindex @code{-fdefault-double-8}, option
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@cindex option, @code{-fdefault-double-8}
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Set the @code{DOUBLE PRECISION} type to an 8 byte wide type.
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@item -fdefault-integer-8
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@cindex @code{-fdefault-integer-8}, option
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@cindex option, @code{-fdefault-integer-8}
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Set the default integer and logical types to an 8 byte wide type.
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Do nothing if this is already the default.
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@item -fdefault-real-8
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@cindex @code{-fdefault-real-8}, option
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@cindex option, @code{-fdefault-real-8}
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Set the default real type to an 8 byte wide type.
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Do nothing if this is already the default.
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@item -fdollar-ok
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@cindex @code{-fdollar-ok} option
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@cindex option, @code{-fdollar-ok}
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@cindex dollar sign
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@cindex symbol names
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@cindex character set
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Allow @samp{$} as a valid character in a symbol name.
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@item -fno-backslash
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@cindex @code{-fno-backslash} option
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@cindex option, @code{-fno-backslash}
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@cindex backslash
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@cindex escape characters
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Change the interpretation of backslashes in string literals from
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``C-style'' escape characters to a single backslash character.
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@item -ffixed-line-length-@var{n}
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@cindex @code{-ffixed-line-length-}@var{n} option
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@cindex option, @code{-ffixed-line-length-}@var{n}
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@cindex source file format
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@cindex lines, length
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@cindex length of source lines
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@cindex fixed form
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@cindex limits, lengths of source lines
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Set column after which characters are ignored in typical fixed-form
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lines in the source file, and through which spaces are assumed (as
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if padded to that length) after the ends of short fixed-form lines.
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@cindex card image
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@cindex extended-source option
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Popular values for @var{n} include 72 (the
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standard and the default), 80 (card image), and 132 (corresponding
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to ``extended-source'' options in some popular compilers).
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@var{n} may also be @samp{none}, meaning that the entire line is meaningful
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and that continued character constants never have implicit spaces appended
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to them to fill out the line.
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@option{-ffixed-line-length-0} means the same thing as
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@option{-ffixed-line-length-none}.
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@item -ffree-line-length-@var{n}
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@cindex @code{-ffree-line-length-}@var{n} option
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@cindex option, @code{-ffree-line-length-}@var{n}
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@cindex source file format
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@cindex lines, length
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@cindex length of source lines
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@cindex free form
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@cindex limits, lengths of source lines
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Set column after which characters are ignored in typical free-form
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lines in the source file. The default value is 132.
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@var{n} may be @samp{none}, meaning that the entire line is meaningful.
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@option{-ffree-line-length-0} means the same thing as
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@option{-ffree-line-length-none}.
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@item -fmax-identifier-length=@var{n}
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@cindex @code{-fmax-identifier-length=}@var{n} option
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@cindex option @option{-fmax-identifier-length=}@var{n}
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Specify the maximum allowed identifier length. Typical values are
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31 (Fortran 95) and 63 (Fortran 2003).
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@item -fimplicit-none
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@cindex @code{-fimplicit-none} option
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@cindex option, @code{-fimplicit-none}
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Specify that no implicit typing is allowed, unless overridden by explicit
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@code{IMPLICIT} statements. This is the equivalent of adding
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@code{implicit none} to the start of every procedure.
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@item -fcray-pointer
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@cindex @code{-fcray-pointer} option
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@cindex option, @code{-fcray-pointer}
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Enable the Cray pointer extension, which provides C-like pointer
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functionality.
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@item -fopenmp
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@cindex @code{-fopenmp} option
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@cindex option, @code{-fopenmp}
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@cindex OpenMP
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Enable the OpenMP extensions. This includes OpenMP @code{!$omp} directives
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in free form
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and @code{c$omp}, @code{*$omp} and @code{!$omp} directives in fixed form,
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@code{!$} conditional compilation sentinels in free form
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and @code{c$}, @code{*$} and @code{!$} sentinels in fixed form,
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and when linking arranges for the OpenMP runtime library to be linked
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in.
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@item -frange-check
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@cindex @code{-frange-check} option
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@cindex option, @code{-frange-check}
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Enable range checking on results of simplification of constant
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expressions during compilation. For example, by default, GNU Fortran
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will give an overflow error at compile time when simplifying @code{a =
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EXP(1000)}. With @option{-fno-range-check}, no error will be given and
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the variable @code{a} will be assigned the value @code{+Infinity}.
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Similarly, @code{DATA i/Z'FFFFFFFF'/} will result in an integer overflow
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on most systems, but with @option{-fno-range-check} the value will
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``wrap around'' and @code{i} will be initialized to @math{-1} instead.
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@item -std=@var{std}
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@cindex @code{-std=}@var{std} option
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@cindex option, @code{-std=}@var{std}
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Conform to the specified standard. The default value for @var{std} is
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@samp{gnu}; a superset of the Fortran 95 standard which includes all
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of the GNU extensions recommended for use in new code. The @samp{legacy}
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value also includes obsolete extensions that may be required for old
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non-standard programs. Strict conformance to the Fortran 95 and Fortran 2003
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standards is specified by @samp{f95} and @samp{f2003}, respectively.
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@end table
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@node Error and Warning Options
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@section Options to Request or Suppress Errors and Warnings
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@cindex options, warnings
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@cindex options, errors
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@cindex warnings, suppressing
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@cindex messages, error
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@cindex messages, warning
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@cindex suppressing warnings
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Errors are diagnostic messages that report that the GNU Fortran compiler
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cannot compile the relevant piece of source code. The compiler will
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continue to process the program in an attempt to report further errors
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to aid in debugging, but will not produce any compiled output.
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Warnings are diagnostic messages that report constructions which
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are not inherently erroneous but which are risky or suggest there is
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likely to be a bug in the program. Unless @option{-Werror} is specified,
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they do not prevent compilation of the program.
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You can request many specific warnings with options beginning @option{-W},
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for example @option{-Wimplicit} to request warnings on implicit
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declarations. Each of these specific warning options also has a
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negative form beginning @option{-Wno-} to turn off warnings;
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for example, @option{-Wno-implicit}. This manual lists only one of the
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two forms, whichever is not the default.
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These options control the amount and kinds of errors and warnings produced
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by GNU Fortran:
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@table @gcctabopt
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@item -fmax-errors-@var{n}
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@cindex @code{-fmax-errors-}@var{n} option
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@cindex option, @code{-fmax-errors-}@var{n}
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@cindex errors, limiting
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Limits the maximum number of error messages to @var{n}, at which point
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GNU Fortran bails out rather than attempting to continue processing the
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source code. If @var{n} is 0, there is no limit on the number of error
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messages produced.
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@item -fsyntax-only
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@cindex @code{-fsyntax-only} option
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@cindex option, @code{-fsyntax-only}
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@cindex syntax checking
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Check the code for syntax errors, but don't do anything beyond that.
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@item -pedantic
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@cindex @code{-pedantic} option
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@cindex option, @code{-pedantic}
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Issue warnings for uses of extensions to Fortran 95.
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@option{-pedantic} also applies to C-language constructs where they
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occur in GNU Fortran source files, such as use of @samp{\e} in a
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character constant within a directive like @code{#include}.
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Valid Fortran 95 programs should compile properly with or without
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this option.
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However, without this option, certain GNU extensions and traditional
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Fortran features are supported as well.
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With this option, many of them are rejected.
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Some users try to use @option{-pedantic} to check programs for conformance.
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They soon find that it does not do quite what they want---it finds some
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nonstandard practices, but not all.
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However, improvements to GNU Fortran in this area are welcome.
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This should be used in conjunction with @option{-std=f95} or
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@option{-std=f2003}.
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@item -pedantic-errors
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@cindex @code{-pedantic-errors} option
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@cindex option, @code{-pedantic-errors}
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Like @option{-pedantic}, except that errors are produced rather than
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warnings.
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@item -w
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@cindex @code{-w} option
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@cindex option, @code{-w}
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Inhibit all warning messages.
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@item -Wall
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@cindex @code{-Wall} option
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@cindex option, @code{-Wall}
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@cindex all warnings
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@cindex warnings, all
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Enables commonly used warning options pertaining to usage that
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we recommend avoiding and that we believe are easy to avoid.
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This currently includes @option{-Waliasing},
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@option{-Wampersand}, @option{-Wsurprising}, @option{-Wnonstd-intrinsic},
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@option{-Wno-tabs}, and @option{-Wline-truncation}.
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@item -Waliasing
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@cindex @code{-Waliasing} option
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@cindex option, @code{-Waliasing}
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@cindex aliasing
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Warn about possible aliasing of dummy arguments. Specifically, it warns
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if the same actual argument is associated with a dummy argument with
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@code{INTENT(IN)} and a dummy argument with @code{INTENT(OUT)} in a call
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with an explicit interface.
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The following example will trigger the warning.
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@smallexample
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interface
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subroutine bar(a,b)
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integer, intent(in) :: a
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integer, intent(out) :: b
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end subroutine
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end interface
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integer :: a
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call bar(a,a)
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@end smallexample
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@item -Wampersand
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@cindex @code{-Wampersand} option
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@cindex option, @code{-Wampersand}
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@cindex ampersand
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Warn about missing ampersand in continued character constants. The warning is
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given with @option{-Wampersand}, @option{-pedantic}, @option{-std=f95}, and
|
|
@option{-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.
|
|
|
|
@item -Wconversion
|
|
@cindex @code{-Wconversion} option
|
|
@cindex option, @code{-Wconversion}
|
|
@cindex conversion
|
|
Warn about implicit conversions between different types.
|
|
|
|
@item -Wimplicit-interface
|
|
@cindex @code{-Wimplicit-interface} option
|
|
@cindex option, @code{-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.
|
|
|
|
@item -Wnonstd-intrinsic
|
|
@cindex @code{-Wnonstd-intrinsic} option
|
|
@cindex option, @code{-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.
|
|
|
|
@item -Wsurprising
|
|
@cindex @code{-Wsurprising} option
|
|
@cindex option, @code{-Wsurprising}
|
|
@cindex Suspicious code
|
|
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:
|
|
|
|
@itemize @bullet
|
|
@item
|
|
An INTEGER SELECT construct has a CASE that can never be matched as its
|
|
lower value is greater than its upper value.
|
|
|
|
@item
|
|
A LOGICAL SELECT construct has three CASE statements.
|
|
@end itemize
|
|
|
|
@item -Wtabs
|
|
@cindex @code{-Wtabs} option
|
|
@cindex option, @code{-Wtabs}
|
|
@cindex Tabs
|
|
By default, tabs are accepted as whitespace, but tabs are not members
|
|
of the Fortran Character Set. @option{-Wno-tabs} will cause a warning
|
|
to be issued if a tab is encountered. Note, @option{-Wno-tabs} is active
|
|
for @option{-pedantic}, @option{-std=f95}, and @option{-Wall}.
|
|
|
|
@item -Wunderflow
|
|
@cindex @code{-Wunderflow} option
|
|
@cindex option, @code{-Wunderflow}
|
|
@cindex UNDERFLOW
|
|
Produce a warning when numerical constant expressions are
|
|
encountered, which yield an UNDERFLOW during compilation.
|
|
|
|
@item -Werror
|
|
@cindex @code{-Werror} option
|
|
@cindex option, @code{-Werror}
|
|
Turns all warnings into errors.
|
|
|
|
@item -W
|
|
@cindex @code{-W} option
|
|
@cindex option, @code{-W}
|
|
@cindex extra warnings
|
|
@cindex warnings, extra
|
|
Turns on ``extra warnings'' and, if optimization is specified
|
|
via @option{-O}, the @option{-Wuninitialized} option.
|
|
(This might change in future versions of GNU Fortran.)
|
|
@end table
|
|
|
|
@xref{Error and Warning Options,,Options to Request or Suppress Errors and
|
|
Warnings, gcc,Using the GNU Compiler Collection (GCC)}, for information on
|
|
more options offered by the GBE shared by @command{gfortran}, @command{gcc}
|
|
and other GNU compilers.
|
|
|
|
Some of these have no effect when compiling programs written in Fortran.
|
|
|
|
@node Debugging Options
|
|
@section Options for Debugging Your Program or GNU Fortran
|
|
@cindex options, debugging
|
|
@cindex debugging information options
|
|
|
|
GNU Fortran has various special options that are used for debugging
|
|
either your program or the GNU Fortran compiler.
|
|
|
|
@table @gcctabopt
|
|
@item -fdump-parse-tree
|
|
@cindex @code{-fdump-parse-tree} option
|
|
@cindex option, @code{-fdump-parse-tree}
|
|
Output the internal parse tree before starting code generation. Only
|
|
really useful for debugging the GNU Fortran compiler itself.
|
|
|
|
@item -ffpe-trap=@var{list}
|
|
@cindex @code{-ffpe-trap=}@var{list} option
|
|
@cindex option, @code{-ffpe-trap=}@var{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. @var{list} is a (possibly empty) comma-separated
|
|
list of the following IEEE exceptions: @samp{invalid} (invalid floating
|
|
point operation, such as @code{SQRT(-1.0)}), @samp{zero} (division by
|
|
zero), @samp{overflow} (overflow in a floating point operation),
|
|
@samp{underflow} (underflow in a floating point operation),
|
|
@samp{precision} (loss of precision during operation) and @samp{denormal}
|
|
(operation produced a denormal value).
|
|
|
|
@cindex -fdump-core option
|
|
@cindex options, -fdump-core
|
|
@item -fdump-core
|
|
@cindex core
|
|
Request that a core-dump file is written to disk when a runtime error
|
|
is encountered on systems that support core dumps. This option is
|
|
only effective for the compilation of the Fortran main program.
|
|
|
|
@end table
|
|
|
|
@xref{Debugging Options,,Options for Debugging Your Program or GCC,
|
|
gcc,Using the GNU Compiler Collection (GCC)}, for more information on
|
|
debugging options.
|
|
|
|
@node Directory Options
|
|
@section Options for Directory Search
|
|
@cindex directory, options
|
|
@cindex options, directory search
|
|
@cindex search path
|
|
@cindex INCLUDE directive
|
|
@cindex directive, INCLUDE
|
|
These options affect how GNU Fortran searches
|
|
for files specified by the @code{INCLUDE} directive and where it searches
|
|
for previously compiled modules.
|
|
|
|
It also affects the search paths used by @command{cpp} when used to preprocess
|
|
Fortran source.
|
|
|
|
@table @gcctabopt
|
|
@item -I@var{dir}
|
|
@cindex @code{-I}@var{dir} option
|
|
@cindex option, @code{-I}@var{dir}
|
|
@cindex directory, search paths for inclusion
|
|
@cindex inclusion, directory search paths for
|
|
@cindex search paths, for included files
|
|
@cindex paths, search
|
|
@cindex module search path
|
|
These affect interpretation of the @code{INCLUDE} directive
|
|
(as well as of the @code{#include} directive of the @command{cpp}
|
|
preprocessor).
|
|
|
|
Also note that the general behavior of @option{-I} and
|
|
@code{INCLUDE} is pretty much the same as of @option{-I} with
|
|
@code{#include} in the @command{cpp} preprocessor, with regard to
|
|
looking for @file{header.gcc} files and other such things.
|
|
|
|
This path is also used to search for @file{.mod} files when previously
|
|
compiled modules are required by a @code{USE} statement.
|
|
|
|
@xref{Directory Options,,Options for Directory Search,
|
|
gcc,Using the GNU Compiler Collection (GCC)}, for information on the
|
|
@option{-I} option.
|
|
|
|
@item -M@var{dir}
|
|
@item -J@var{dir}
|
|
@cindex @code{-M}@var{dir} option
|
|
@cindex option, -@code{-M}@var{dir}
|
|
@cindex @code{-J}@var{dir} option
|
|
@cindex option, -@code{-J}@var{dir}
|
|
This option specifies where to put @file{.mod} files for compiled modules.
|
|
It is also added to the list of directories to searched by an @code{USE}
|
|
statement.
|
|
|
|
The default is the current directory.
|
|
|
|
@option{-J} is an alias for @option{-M} to avoid conflicts with existing
|
|
GCC options.
|
|
@end table
|
|
|
|
@node Runtime Options
|
|
@section Influencing runtime behavior
|
|
@cindex runtime, options
|
|
|
|
These options affect the runtime behavior of programs compiled with GNU Fortran.
|
|
@table @gcctabopt
|
|
@item -fconvert=@var{conversion}
|
|
@cindex @code{-fconvert=}@var{conversion} option
|
|
@cindex option, @code{-fconvert=}@var{conversion}
|
|
Specify the representation of data for unformatted files. Valid
|
|
values for conversion are: @samp{native}, the default; @samp{swap},
|
|
swap between big- and little-endian; @samp{big-endian}, use big-endian
|
|
representation for unformatted files; @samp{little-endian}, use little-endian
|
|
representation for unformatted files.
|
|
|
|
@emph{This option has an effect only when used in the main program.
|
|
The @code{CONVERT} specifier and the GFORTRAN_CONVERT_UNIT environment
|
|
variable override the default specified by @option{-fconvert}.}
|
|
|
|
@item -frecord-marker=@var{length}
|
|
@cindex @code{-frecord-marker=}@var{length} option
|
|
@cindex option, @code{-frecord-marker=}@var{length}
|
|
Specify the length of record markers for unformatted files.
|
|
Valid values for @var{length} are 4 and 8. Default is 4.
|
|
@emph{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 @option{-frecord-marker=8}.
|
|
|
|
@item -fmax-subrecord-length=@var{length}
|
|
@cindex @code{-fmax-subrecord-length=}@var{length} option
|
|
@cindex option, @code{-fmax-subrecord-length=}@var{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.
|
|
@end table
|
|
|
|
@node Code Gen Options
|
|
@section Options for Code Generation Conventions
|
|
@cindex code generation, conventions
|
|
@cindex options, code generation
|
|
@cindex run-time, options
|
|
|
|
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 @option{-ffoo} would be @option{-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 @option{no-} or adding
|
|
it.
|
|
|
|
@table @gcctabopt
|
|
@item -fno-automatic
|
|
@cindex @code{-fno-automatic} option
|
|
@cindex option, @code{-fno-automatic}
|
|
@cindex SAVE statement
|
|
@cindex statements, SAVE
|
|
Treat each program unit as if the @code{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
|
|
@option{-static}.)
|
|
|
|
@item -ff2c
|
|
@cindex @code{-ff2c} option
|
|
@cindex option, @code{-ff2c}
|
|
@cindex calling convention
|
|
@cindex @command{f2c} calling convention
|
|
@cindex @command{g77} calling convention
|
|
@cindex libf2c calling convention
|
|
Generate code designed to be compatible with code generated
|
|
by @command{g77} and @command{f2c}.
|
|
|
|
The calling conventions used by @command{g77} (originally implemented
|
|
in @command{f2c}) require functions that return type
|
|
default @code{REAL} to actually return the C type @code{double}, and
|
|
functions that return type @code{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 @code{REAL} functions return the C type @code{float}, and
|
|
@code{COMPLEX} functions return the GNU C type @code{complex}.
|
|
Additionally, this option implies the @option{-fsecond-underscore}
|
|
option, unless @option{-fno-second-underscore} is explicitly requested.
|
|
|
|
This does not affect the generation of code that interfaces with
|
|
the @command{libgfortran} library.
|
|
|
|
@emph{Caution:} It is not a good idea to mix Fortran code compiled with
|
|
@option{-ff2c} with code compiled with the default @option{-fno-f2c}
|
|
calling conventions as, calling @code{COMPLEX} or default @code{REAL}
|
|
functions between program parts which were compiled with different
|
|
calling conventions will break at execution time.
|
|
|
|
@emph{Caution:} This will break code which passes intrinsic functions
|
|
of type default @code{REAL} or @code{COMPLEX} as actual arguments, as
|
|
the library implementations use the @option{-fno-f2c} calling conventions.
|
|
|
|
@item -fno-underscoring
|
|
@cindex @code{-fno-underscoring option}
|
|
@cindex option, @code{-fno-underscoring}
|
|
@cindex underscore
|
|
@cindex symbol names, underscores
|
|
@cindex transforming symbol names
|
|
@cindex symbol names, transforming
|
|
Do not transform names of entities specified in the Fortran
|
|
source file by appending underscores to them.
|
|
|
|
With @option{-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.
|
|
|
|
@emph{Caution}: The default behavior of GNU Fortran is
|
|
incompatible with @command{f2c} and @command{g77}, please use the
|
|
@option{-ff2c} option if you want object files compiled with
|
|
GNU Fortran to be compatible with object code created with these
|
|
tools.
|
|
|
|
Use of @option{-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 @option{-funderscoring}, and assuming other defaults like
|
|
@option{-fcase-lower} and that @code{j()} and @code{max_count()} are
|
|
external functions while @code{my_var} and @code{lvar} are local variables,
|
|
a statement like
|
|
@smallexample
|
|
I = J() + MAX_COUNT (MY_VAR, LVAR)
|
|
@end smallexample
|
|
@noindent
|
|
is implemented as something akin to:
|
|
@smallexample
|
|
i = j_() + max_count__(&my_var__, &lvar);
|
|
@end smallexample
|
|
|
|
With @option{-fno-underscoring}, the same statement is implemented as:
|
|
|
|
@smallexample
|
|
i = j() + max_count(&my_var, &lvar);
|
|
@end smallexample
|
|
|
|
Use of @option{-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 @emph{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 @option{-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.
|
|
|
|
@item -fsecond-underscore
|
|
@cindex @code{-fsecond-underscore option}
|
|
@cindex option, @code{-fsecond-underscore}
|
|
@cindex underscore
|
|
@cindex symbol names, underscores
|
|
@cindex transforming symbol names
|
|
@cindex symbol names, transforming
|
|
@cindex @command{f2c} calling convention
|
|
@cindex @command{g77} calling convention
|
|
@cindex libf2c calling convention
|
|
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 @option{-fno-underscoring} is
|
|
in effect. It is implied by the @option{-ff2c} option.
|
|
|
|
Otherwise, with this option, an external name such as @code{MAX_COUNT}
|
|
is implemented as a reference to the link-time external symbol
|
|
@code{max_count__}, instead of @code{max_count_}. This is required
|
|
for compatibility with @command{g77} and @command{f2c}, and is implied
|
|
by use of the @option{-ff2c} option.
|
|
|
|
@item -fbounds-check
|
|
@cindex @code{-fbounds-check} option
|
|
@cindex option, @code{-fbounds-check}
|
|
@cindex bounds checking
|
|
@cindex range checking
|
|
@cindex array bounds checking
|
|
@cindex subscript checking
|
|
@cindex checking subscripts
|
|
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.
|
|
|
|
@item -fmax-stack-var-size=@var{n}
|
|
@cindex @code{-fmax-stack-var-size} option
|
|
@cindex option, @code{-fmax-stack-var-size}
|
|
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 @var{n} is 32768.
|
|
|
|
@item -fpack-derived
|
|
@cindex @code{-fpack-derived} option
|
|
@cindex option, @code{-fpack-derived}
|
|
@cindex Structure packing
|
|
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.
|
|
|
|
@item -frepack-arrays
|
|
@cindex @code{-frepack-arrays} option
|
|
@cindex option, @code{-frepack-arrays}
|
|
@cindex Repacking 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.
|
|
|
|
@item -fshort-enums
|
|
@cindex @code{-fshort-enums} option
|
|
@cindex option, @code{-fshort-enums}
|
|
This option is provided for interoperability with C code that was
|
|
compiled with the @option{-fshort-enums} option. It will make
|
|
GNU Fortran choose the smallest @code{INTEGER} kind a given
|
|
enumerator set will fit in, and give all its enumerators this kind.
|
|
|
|
@item -fexternal-blas
|
|
@cindex @code{-fexternal-blas} option
|
|
@cindex option, @code{-fexternal-blas}
|
|
This option will make gfortran generate calls to BLAS functions for some
|
|
matrix operations like @code{MATMUL}, instead of using our own
|
|
algorithms, if the size of the matrices involved is larger than a given
|
|
limit (see @option{-fblas-matmul-limit}). This may be profitable if an
|
|
optimized vendor BLAS library is available. The BLAS library will have
|
|
to be specified at link time.
|
|
|
|
@item -fblas-matmul-limit=@var{n}
|
|
@cindex @code{-fblas-matmul-limit} option
|
|
@cindex option, @code{-fblas-matmul-limit}
|
|
Only significant when @option{-fexternal-blas} is in effect.
|
|
Matrix multiplication of matrices with size larger than (or equal to) @var{n}
|
|
will be performed by calls to BLAS functions, while others will be
|
|
handled by @command{gfortran} internal algorithms. If the matrices
|
|
involved are not square, the size comparison is performed using the
|
|
geometric mean of the dimensions of the argument and result matrices.
|
|
|
|
The default value for @var{n} is 30.
|
|
|
|
@end table
|
|
|
|
@xref{Code Gen Options,,Options for Code Generation Conventions,
|
|
gcc,Using the GNU Compiler Collection (GCC)}, for information on more options
|
|
offered by the GBE
|
|
shared by @command{gfortran}, @command{gcc}, and other GNU compilers.
|
|
|
|
|
|
@c man end
|
|
|
|
@node Environment Variables
|
|
@section Environment Variables Affecting @command{gfortran}
|
|
@cindex environment variables
|
|
|
|
@c man begin ENVIRONMENT
|
|
|
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The @command{gfortran} compiler currently does not make use of any environment
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variables to control its operation above and beyond those
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that affect the operation of @command{gcc}.
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@xref{Environment Variables,,Environment Variables Affecting GCC,
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gcc,Using the GNU Compiler Collection (GCC)}, for information on environment
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variables.
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@xref{Runtime}, for environment variables that affect the
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run-time behavior of programs compiled with GNU Fortran.
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@c man end
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