-@c Copyright (C) 2004, 2005
+@c Copyright (C) 2004, 2005, 2006
@c Free Software Foundation, Inc.
-@c This is part of the GFORTRAN manual.
+@c This is part of the GNU Fortran manual.
@c For copying conditions, see the file gfortran.texi.
@ignore
@c man begin COPYRIGHT
-Copyright @copyright{} 2004, 2005
+Copyright @copyright{} 2004, 2005, 2006
Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
@c man end
@c Set file name and title for the man page.
@setfilename gfortran
-@settitle GNU Fortran 95 compiler.
+@settitle GNU Fortran compiler.
@c man begin SYNOPSIS
gfortran [@option{-c}|@option{-S}|@option{-E}]
[@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
@c man end
@c man begin AUTHOR
See the Info entry for @command{gfortran} for contributors to GCC and
-GFORTRAN@.
+GNU Fortran.
@c man end
@end ignore
-@node Invoking GFORTRAN
-@chapter GNU Fortran 95 Command Options
-@cindex GNU Fortran 95 command options
+@node Invoking GNU Fortran
+@chapter GNU Fortran Command Options
+@cindex GNU Fortran command options
@cindex command options
-@cindex options, GNU Fortran 95 command
+@cindex options, @command{gfortran} command
@c man begin DESCRIPTION
The @command{gfortran} command supports all the options supported by the
-@command{gcc} command. Only options specific to gfortran are documented here.
+@command{gcc} command. Only options specific to GNU Fortran are documented here.
@xref{Invoking GCC,,GCC Command Options,gcc,Using the GNU Compiler
Collection (GCC)}, for information
@cindex options, negative forms
@cindex negative forms of options
-All @command{gcc} and @command{gfortran} options
+All GCC and GNU Fortran options
are accepted both by @command{gfortran} and by @command{gcc}
(as well as any other drivers built at the same time,
such as @command{g++}),
-since adding @command{gfortran} to the @command{gcc} distribution
-enables acceptance of @command{gfortran} options
+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;
without explanations.
* Fortran Dialect Options:: Controlling the variant of Fortran language
compiled.
-* Warning Options:: How picky should the compiler be?
+* Error and Warning Options:: How picky should the compiler be?
* Debugging Options:: Symbol tables, measurements, and debugging dumps.
* Directory Options:: Where to find module files
+* Runtime Options:: Influencing runtime behavior
* Code Gen Options:: Specifying conventions for function calls, data layout
and register usage.
-* Environment Variables:: Env vars that affect GNU Fortran.
+* Environment Variables:: Env vars that affect @command{gfortran}.
@end menu
@node Option Summary
@table @emph
@item Fortran Language Options
@xref{Fortran Dialect Options,,Options Controlling Fortran Dialect}.
-@gccoptlist{
--ffree-form -fno-fixed-form @gol
+@gccoptlist{-fall-intrinsics -ffree-form -fno-fixed-form @gol
-fdollar-ok -fimplicit-none -fmax-identifier-length @gol
--std=@var{std} -fd-lines-as-code -fd-lines-as-comments @gol
+-std=@var{std} -fd-lines-as-code -fd-lines-as-comments @gol
-ffixed-line-length-@var{n} -ffixed-line-length-none @gol
-ffree-line-length-@var{n} -ffree-line-length-none @gol
-fdefault-double-8 -fdefault-integer-8 -fdefault-real-8 @gol
--fcray-pointer }
+-fcray-pointer -fopenmp -frange-check }
-@item Warning Options
-@xref{Warning Options,,Options to Request or Suppress Warnings}.
-@gccoptlist{
+@item Error and Warning Options
+@xref{Error and Warning Options,,Options to Request or Suppress Errors
+and Warnings}.
+@gccoptlist{-fmax-errors=@var{n} @gol
-fsyntax-only -pedantic -pedantic-errors @gol
--w -Wall -Waliasing -Wconversion @gol
--Wimplicit-interface -Wnonstd-intrinsics -Wsurprising -Wunderflow @gol
--Wunused-labels -Wline-truncation -W}
+-w -Wall -Waliasing -Wampersand -Wconversion -Wimplicit-interface @gol
+-Wtabs -Wnonstd-intrinsics -Wsurprising -Wunderflow @gol
+-Wline-truncation -W}
@item Debugging Options
@xref{Debugging Options,,Options for Debugging Your Program or GCC}.
-@gccoptlist{
--fdump-parse-tree -ffpe-trap=@var{list}}
+@gccoptlist{-fdump-parse-tree -ffpe-trap=@var{list}}
@item Directory Options
@xref{Directory Options,,Options for Directory Search}.
-@gccoptlist{
--I@var{dir} -M@var{dir}}
+@gccoptlist{-I@var{dir} -M@var{dir}}
+
+@item Runtime Options
+@xref{Runtime Options,,Options for influencing runtime behavior}.
+@gccoptlist{-fconvert=@var{conversion} -frecord-marker=@var{length}}
@item Code Generation Options
@xref{Code Gen Options,,Options for Code Generation Conventions}.
-@gccoptlist{
--fno-automatic -ff2c -fno-underscoring -fsecond-underscore @gol
+@gccoptlist{-fno-automatic -ff2c -fno-underscoring
+-fsecond-underscore @gol
-fbounds-check -fmax-stack-var-size=@var{n} @gol
--fpackderived -frepack-arrays -fshort-enums}
+-fpack-derived -frepack-arrays -fshort-enums -fexternal-blas @gol
+-fblas-matmul-limit=@var{n}}
@end table
@menu
* Fortran Dialect Options:: Controlling the variant of Fortran language
compiled.
-* Warning Options:: How picky should the compiler be?
+* Error and Warning Options:: How picky should the compiler be?
* Debugging Options:: Symbol tables, measurements, and debugging dumps.
* Directory Options:: Where to find module files
+* Runtime Options:: Influencing runtime behavior
* Code Gen Options:: Specifying conventions for function calls, data layout
and register usage.
@end menu
@cindex language, dialect options
@cindex options, dialect
-The following options control the dialect of Fortran
-that the compiler accepts:
+The following options control the details of the Fortran dialect
+accepted by the compiler:
@table @gcctabopt
@cindex -ffree-form option
@item -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.
+older Fortran programs. When neither option is specified, the source
+form is determined by the file extension.
+
+@cindex -fall-intrinsics
+@item -fall-intrinsics
+Accept all of the intrinsic procedures provided in libgfortran
+without regard to the setting of @option{-std}. In particular,
+this option can be quite useful with @option{-std=f95}. Additionally,
+@command{gfortran} will ignore @option{-Wnonstd-intrinsics}.
@cindex option, -fd-lines-as-code
@cindex -fd-lines-as-code, option
@cindex -fd-lines-as-comments, option
@item -fd-lines-as-code
@item -fd-lines-as-comment
-Enables special treating for lines with @samp{d} or @samp{D} in fixed
-form sources. If the @option{-fd-lines-as-code} option is given
-they are treated as if the first column contained a blank. If the
+Enable special treatment for lines beginning with @samp{d} or @samp{D}
+in fixed form sources. If the @option{-fd-lines-as-code} option is
+given they are treated as if the first column contained a blank. If the
@option{-fd-lines-as-comments} option is given, they are treated as
comment lines.
@cindex option, -fdefault-double-8
@cindex -fdefault-double-8, option
@item -fdefault-double-8
-Set the "DOUBLE PRECISION" type to an 8 byte wide.
+Set the @code{DOUBLE PRECISION} type to an 8 byte wide type.
@cindex option, -fdefault-integer-8
@cindex -fdefault-integer-8, option
@item -fno-backslash
@cindex backslash
@cindex escape characters
-Compile switch to change the interpretation of a backslash from
-``C''-style escape characters to a single backslash character.
+Change the interpretation of backslashes in string literals from
+``C-style'' escape characters to a single backslash character.
@cindex -ffixed-line-length-@var{n} option
@cindex options, -ffixed-line-length-@var{n}
@cindex card image
@cindex extended-source option
Popular values for @var{n} include 72 (the
-standard and the default), 80 (card image), and 132 (corresponds
+standard and the default), 80 (card image), and 132 (corresponding
to ``extended-source'' options in some popular compilers).
-@var{n} may be @samp{none}, meaning that the entire line is meaningful
+@var{n} may also be @samp{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.
@option{-ffixed-line-length-0} means the same thing as
@cindex free form
@cindex limits, lengths of source lines
Set column after which characters are ignored in typical free-form
-lines in the source file. For free-form, the default value is 132.
+lines in the source file. The default value is 132.
@var{n} may be @samp{none}, meaning that the entire line is meaningful.
@option{-ffree-line-length-0} means the same thing as
@option{-ffree-line-length-none}.
@cindex option -fmax-identifier-length=@var{n}
@item -fmax-identifier-length=@var{n}
Specify the maximum allowed identifier length. Typical values are
-31 (Fortran 95) and 63 (Fortran 200x).
+31 (Fortran 95) and 63 (Fortran 2003).
@cindex -fimplicit-none option
@cindex options, -fimplicit-none
@item -fimplicit-none
Specify that no implicit typing is allowed, unless overridden by explicit
-@samp{IMPLICIT} statements. This is the equivalent of adding
-@samp{implicit none} to the start of every procedure.
+@code{IMPLICIT} statements. This is the equivalent of adding
+@code{implicit none} to the start of every procedure.
@cindex -fcray-pointer option
@cindex options, -fcray-pointer
@item -fcray-pointer
-Enables the Cray pointer extension, which provides a C-like pointer.
+Enable the Cray pointer extension, which provides C-like pointer
+functionality.
+
+@cindex -fopenmp
+@cindex options, -fopenmp
+@item -fopenmp
+Enable the OpenMP extensions. This includes OpenMP @code{!$omp} directives
+in free form
+and @code{c$omp}, @code{*$omp} and @code{!$omp} directives in fixed form,
+@code{!$} conditional compilation sentinels in free form
+and @code{c$}, @code{*$} and @code{!$} sentinels in fixed form,
+and when linking arranges for the OpenMP runtime library to be linked
+in.
+
+@cindex -frange-check
+@cindex options, -frange-check
+@item -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 @code{a =
+EXP(1000)}. With @option{-fno-range-check}, no error will be given and
+the variable @code{a} will be assigned the value @code{+Infinity}.
+Similarly, @code{DATA i/Z'FFFFFFFF'/} will result in an integer overflow
+on most systems, but with @option{-fno-range-check} the value will
+``wrap around'' and @code{i} will be initialized to @math{-1} instead.
@cindex -std=@var{std} option
@cindex option, -std=@var{std}
@item -std=@var{std}
-Conform to the specified standard. Allowed values for @var{std} are
-@samp{gnu}, @samp{f95}, @samp{f2003} and @samp{legacy}.
+Conform to the specified standard. The default value for @var{std} is
+@samp{gnu}; a superset of the Fortran 95 standard which includes all
+of the GNU extensions recommended for use in new code. The @samp{legacy}
+value also includes obsolete extensions that may be required for old
+non-standard programs. Strict conformance to the Fortran 95 and Fortran 2003
+standards is specified by @samp{f95} and @samp{f2003}, respectively.
@end table
-@node Warning Options
-@section Options to Request or Suppress Warnings
+@node Error and Warning Options
+@section Options to Request or Suppress Errors and Warnings
@cindex options, warnings
+@cindex options, errors
@cindex warnings, suppressing
+@cindex messages, error
@cindex messages, warning
@cindex suppressing 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
-might have been an error.
+are not inherently erroneous but which are risky or suggest there is
+likely to be a bug in the program. Unless @option{-Werrors} is specified,
+they do not prevent compilation of the program.
You can request many specific warnings with options beginning @option{-W},
for example @option{-Wimplicit} to request warnings on implicit
for example, @option{-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:
+These options control the amount and kinds of errors and warnings produced
+by GNU Fortran:
@table @gcctabopt
+@cindex errors, limiting
+@cindex -fmax-errors-@var{n} option
+@cindex options, -fmax-errors-@var{n}
+@item -fmax-errors-@var{n}
+Limits the maximum number of error messages to @var{n}, at which point
+GNU Fortran bails out rather than attempting to continue processing the
+source code. If @var{n} is 0, there is no limit on the number of error
+messages produced.
+
@cindex syntax checking
@cindex -fsyntax-only option
@cindex options, -fsyntax-only
@cindex -pedantic option
@cindex options, -pedantic
@item -pedantic
-Issue warnings for uses of extensions to FORTRAN 95.
+Issue warnings for uses of extensions to Fortran 95.
@option{-pedantic} also applies to C-language constructs where they
occur in GNU Fortran source files, such as use of @samp{\e} in a
-character constant within a directive like @samp{#include}.
+character constant within a directive like @code{#include}.
-Valid FORTRAN 95 programs should compile properly with or without
+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.
Some users try to use @option{-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 @command{gfortran} in this area are welcome.
+However, improvements to GNU Fortran in this area are welcome.
This should be used in conjunction with -std=@var{std}.
@item -Wall
@cindex all warnings
@cindex warnings, all
-Enables commonly used warning options that which pertain to usage that
-we recommend avoiding and that we believe is easy to avoid.
-This currently includes @option{-Wunused-labels}, @option{-Waliasing},
-@option{-Wsurprising}, @option{-Wnonstd-intrinsic} and
-@option{-Wline-truncation}.
+Enables commonly used warning options pertaining to usage that
+we recommend avoiding and that we believe are easy to avoid.
+This currently includes @option{-Waliasing},
+@option{-Wampersand}, @option{-Wsurprising}, @option{-Wnonstd-intrinsic},
+@option{-Wno-tabs}, and @option{-Wline-truncation}.
@cindex -Waliasing option
@cindex aliasing
Warn about possible aliasing of dummy arguments. Specifically, it warns
if the same actual argument is associated with a dummy argument with
-@code{intent(in)} and a dummy argument with @code{intent(out)} in a call
+@code{INTENT(IN)} and a dummy argument with @code{INTENT(OUT)} in a call
with an explicit interface.
The following example will trigger the warning.
@end smallexample
+@cindex -Wampersand option
+@cindex options, -Wampersand
+@item -Wampersand
+@cindex ampersand
+Warn about missing ampersand in continued character constants. The warning is
+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.
+
+
@cindex -Wconversion option
@cindex options, -Wconversion
@item -Wconversion
@cindex -Wimplicit-interface option
@cindex options, -Wimplicit-interface
@item -Wimplicit-interface
-Warn about when procedure are called without an explicit 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.
A LOGICAL SELECT construct has three CASE statements.
@end itemize
+
+@cindex -Wtabs
+@cindex options, -Wtabs
+@item -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}.
+
+
@cindex -Wunderflow
@cindex options, -Wunderflow
@item -Wunderflow
encountered, which yield an UNDERFLOW during compilation.
-@cindex -Wunused-labels option
-@cindex options, -Wunused-labels
-@item -Wunused-labels
-@cindex unused labels
-@cindex labels, unused
-Warn whenever a label is defined but never referenced.
-
-
@cindex -Werror
@cindex options, -Werror
@item -Werror
@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 @command{gfortran}
+(This might change in future versions of GNU Fortran.)
@end table
-@xref{Warning Options,,Options to Request or Suppress 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.
+@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.
@cindex debugging information options
GNU Fortran has various special options that are used for debugging
-either your program or @command{gfortran}
+either your program or the GNU Fortran compiler.
@table @gcctabopt
@cindex -fdump-parse-tree option
@cindex option, -fdump-parse-tree
@item -fdump-parse-tree
Output the internal parse tree before starting code generation. Only
-really useful for debugging gfortran itself.
+really useful for debugging the GNU Fortran compiler itself.
@end table
@table @gcctabopt
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
+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 denormal value).
+(operation produced a denormal value).
@end table
@xref{Debugging Options,,Options for Debugging Your Program or GCC,
@cindex INCLUDE directive
@cindex directive, INCLUDE
-These options affect how @command{gfortran} searches
+These options affect how GNU Fortran searches
for files specified by the @code{INCLUDE} directive and where it searches
for previously compiled modules.
@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 @samp{.mod} files when previously
+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,
@cindex option, -Mdir
@item -M@var{dir}
@item -J@var{dir}
-This option specifies where to put @samp{.mod} files for compiled modules.
+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.
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
+@cindex -fconvert=@var{conversion} option
+@item -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}.}
+
+@cindex -frecord-marker=@var{length}
+@item -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}.
+
+@cindex -fmax-subrecord-length=@var{length}
+@item -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
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
+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 @code{-ff2c} with code compiled with the default @code{-fno-f2c}
+@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 @command{-fno-f2c} calling conventions.
+the library implementations use the @option{-fno-f2c} calling conventions.
@cindex @option{-fno-underscoring option}
@cindex options, @option{-fno-underscoring}
Do not transform names of entities specified in the Fortran
source file by appending underscores to them.
-With @option{-funderscoring} in effect, @command{gfortran} appends one
+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 @command{gfortran} is
+@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
-@option{gfortran} to be compatible with object code created with these
+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
+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 @samp{j()} and @samp{max_count()} are
-external functions while @samp{my_var} and @samp{lvar} are local variables,
+@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
@end smallexample
Use of @option{-fno-underscoring} allows direct specification of
-user-defined names while debugging and when interfacing @command{gfortran}
+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 @command{gfortran} for an external name matches 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 @command{gfortran} to link to code produced
+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
cases---they might occur at program run time, and show up only as
buggy behavior at run time.
-In future versions of @command{gfortran} we hope to improve naming and linking
+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
@cindex @command{f2c} calling convention
@cindex @command{g77} calling convention
@cindex libf2c calling convention
-By default, @command{gfortran} appends an underscore to external
-names. If this option is used @command{gfortran} appends two
+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. (@command{gfortran} also appends two underscores to
+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 @samp{MAX_COUNT}
+Otherwise, with this option, an external name such as @code{MAX_COUNT}
is implemented as a reference to the link-time external symbol
-@samp{max_count__}, instead of @samp{max_count_}. This is required
+@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.
This option currently only affects local arrays declared with constant
bounds, and may not apply to all character variables.
-Future versions of @command{gfortran} may improve this behavior.
+Future versions of GNU Fortran may improve this behavior.
The default value for @var{n} is 32768.
-@cindex -fpackderived
-@item -fpackderived
+@cindex -fpack-derived
+@item -fpack-derived
@cindex Structure packing
-This option tells gfortran to pack derived type members as closely as
+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.
@cindex -frepack-arrays option
@item -frepack-arrays
@cindex Repacking arrays
-In some circumstances @command{gfortran} may pass assumed shape array
-sections via a descriptor describing a discontiguous area of memory.
+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 discontiguous.
+is noncontiguous.
@cindex -fshort-enums
@item -fshort-enums
This option is provided for interoperability with C code that was
compiled with the @command{-fshort-enums} option. It will make
-@command{gfortran} choose the smallest @code{INTEGER} kind a given
+GNU Fortran choose the smallest @code{INTEGER} kind a given
enumerator set will fit in, and give all its enumerators this kind.
+
+@cindex -fexternal-blas
+@item -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 @command{-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.
+
+@cindex -fblas-matmul-limit
+@item -fblas-matmul-limit=@var{n}
+Only significant when @command{-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.
+shared by @command{gfortran}, @command{gcc}, and other GNU compilers.
@c man end
@node Environment Variables
-@section Environment Variables Affecting GNU Fortran
+@section Environment Variables Affecting @command{gfortran}
@cindex environment variables
@c man begin ENVIRONMENT
-GNU Fortran 95 currently does not make use of any environment
+The @command{gfortran} compiler currently does not make use of any environment
variables to control its operation above and beyond those
that affect the operation of @command{gcc}.
gcc,Using the GNU Compiler Collection (GCC)}, for information on environment
variables.
+@xref{Runtime}, for environment variables that affect the
+run-time behavior of programs compiled with GNU Fortran.
@c man end
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