gfortran
(1)
Name
gfortran - GNU Fortran compiler
Synopsis
gfortran [-c|-S|-E]
[-g] [-pg] [-Olevel]
[-Wwarn...] [-pedantic]
[-Idir...] [-Ldir...]
[-Dmacro[=defn]...] [-Umacro]
[-foption...]
[-mmachine-option...]
[-o outfile] infile...
Only the most useful options are listed here; see below for
the remainder.
Description
GNU GFORTRAN(1)
NAME
gfortran - GNU Fortran compiler
SYNOPSIS
gfortran [-c|-S|-E]
[-g] [-pg] [-Olevel]
[-Wwarn...] [-pedantic]
[-Idir...] [-Ldir...]
[-Dmacro[=defn]...] [-Umacro]
[-foption...]
[-mmachine-option...]
[-o outfile] infile...
Only the most useful options are listed here; see below for
the remainder.
DESCRIPTION
The gfortran command supports all the options supported by
the gcc command. Only options specific to GNU Fortran are
documented here.
All GCC and GNU Fortran options are accepted both by
gfortran and by gcc (as well as any other drivers built at
the same time, such as g++), since adding GNU Fortran to the
GCC distribution enables acceptance of GNU Fortran options
by all of the relevant drivers.
In some cases, options have positive and negative forms; the
negative form of -ffoo would be -fno-foo. This manual
documents only one of these two forms, whichever one is not
the default.
OPTIONS
Here is a summary of all the options specific to GNU
Fortran, grouped by type. Explanations are in the following
sections.
Fortran Language Options
-fall-intrinsics -fbackslash -fcray-pointer
-fd-lines-as-code -fd-lines-as-comments
-fdefault-double-8 -fdefault-integer-8 -fdefault-real-8
-fdollar-ok -ffixed-line-length-n
-ffixed-line-length-none -ffree-form
-ffree-line-length-n -ffree-line-length-none
-fimplicit-none -finteger-4-integer-8
-fmax-identifier-length -fmodule-private -fno-fixed-form
-fno-range-check -fopenmp -freal-4-real-10
-freal-4-real-16 -freal-4-real-8 -freal-8-real-10
-freal-8-real-16 -freal-8-real-4 -std=std
Preprocessing Options
-A-question[=answer] -Aquestion=answer -C -CC
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-Dmacro[=defn] -H -P -Umacro -cpp -dD -dI -dM -dN -dU
-fworking-directory -imultilib dir -iprefix file -iquote
-isysroot dir -isystem dir -nocpp -nostdinc -undef
Error and Warning Options
-Waliasing -Wall -Wampersand -Warray-bounds
-Wc-binding-type -Wcharacter-truncation -Wconversion
-Wfunction-elimination -Wimplicit-interface
-Wimplicit-procedure -Wintrinsic-shadow -Wintrinsics-std
-Wline-truncation -Wno-align-commons -Wno-tabs
-Wreal-q-constant -Wsurprising -Wunderflow
-Wunused-parameter -Wrealloc-lhs Wrealloc-lhs-all
-Wtarget-lifetime -fmax-errors=n -fsyntax-only -pedantic
-pedantic-errors
Debugging Options
-fbacktrace -fdump-fortran-optimized
-fdump-fortran-original -fdump-parse-tree
-ffpe-trap=list
Directory Options
-Idir -Jdir -fintrinsic-modules-path dir
Link Options
-static-libgfortran
Runtime Options
-fconvert=conversion -fmax-subrecord-length=length
-frecord-marker=length -fsign-zero
Code Generation Options
-faggressive-function-elimination -fblas-matmul-limit=n
-fbounds-check -fcheck-array-temporaries
-fcheck=<all|array-temps|bounds|do|mem|pointer|recursion>
-fcoarray=<none|single|lib> -fexternal-blas -ff2c
-ffrontend-optimize -finit-character=n -finit-integer=n
-finit-local-zero -finit-logical=<true|false>
-finit-real=<zero|inf|-inf|nan|snan>
-fmax-array-constructor=n -fmax-stack-var-size=n
-fno-align-commons -fno-automatic -fno-protect-parens
-fno-underscoring -fno-whole-file -fsecond-underscore
-fpack-derived -frealloc-lhs -frecursive -frepack-arrays
-fshort-enums -fstack-arrays
Options controlling Fortran dialect
The following options control the details of the Fortran
dialect accepted by the compiler:
-ffree-form
-ffixed-form
Specify the layout used by the source file. The free
form layout was introduced in Fortran 90. Fixed form
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was traditionally used in older Fortran programs. When
neither option is specified, the source form is
determined by the file extension.
-fall-intrinsics
This option causes all intrinsic procedures (including
the GNU-specific extensions) to be accepted. This can
be useful with -std=f95 to force standard-compliance but
get access to the full range of intrinsics available
with gfortran. As a consequence, -Wintrinsics-std will
be ignored and no user-defined procedure with the same
name as any intrinsic will be called except when it is
explicitly declared "EXTERNAL".
-fd-lines-as-code
-fd-lines-as-comments
Enable special treatment for lines beginning with "d" or
"D" in fixed form sources. If the -fd-lines-as-code
option is given they are treated as if the first column
contained a blank. If the -fd-lines-as-comments option
is given, they are treated as comment lines.
-fdefault-double-8
Set the "DOUBLE PRECISION" type to an 8 byte wide type.
If -fdefault-real-8 is given, "DOUBLE PRECISION" would
instead be promoted to 16 bytes if possible, and
-fdefault-double-8 can be used to prevent this. The
kind of real constants like "1.d0" will not be changed
by -fdefault-real-8 though, so also -fdefault-double-8
does not affect it.
-fdefault-integer-8
Set the default integer and logical types to an 8 byte
wide type. Do nothing if this is already the default.
This option also affects the kind of integer constants
like 42.
-fdefault-real-8
Set the default real type to an 8 byte wide type. Do
nothing if this is already the default. This option
also affects the kind of non-double real constants like
1.0, and does promote the default width of "DOUBLE
PRECISION" to 16 bytes if possible, unless
"-fdefault-double-8" is given, too.
-fdollar-ok
Allow $ as a valid non-first character in a symbol name.
Symbols that start with $ are rejected since it is
unclear which rules to apply to implicit typing as
different vendors implement different rules. Using $ in
"IMPLICIT" statements is also rejected.
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-fbackslash
Change the interpretation of backslashes in string
literals from a single backslash character to "C-style"
escape characters. The following combinations are
expanded "\a", "\b", "\f", "\n", "\r", "\t", "\v", "\\",
and "\0" to the ASCII characters alert, backspace, form
feed, newline, carriage return, horizontal tab, vertical
tab, backslash, and NUL, respectively. Additionally,
"\x"nn, "\u"nnnn and "\U"nnnnnnnn (where each n is a
hexadecimal digit) are translated into the Unicode
characters corresponding to the specified code points.
All other combinations of a character preceded by \ are
unexpanded.
-fmodule-private
Set the default accessibility of module entities to
"PRIVATE". Use-associated entities will not be
accessible unless they are explicitly declared as
"PUBLIC".
-ffixed-line-length-n
Set column after which characters are ignored in typical
fixed-form lines in the source file, and through which
spaces are assumed (as if padded to that length) after
the ends of short fixed-form lines.
Popular values for n include 72 (the standard and the
default), 80 (card image), and 132 (corresponding to
"extended-source" options in some popular compilers). n
may also be none, meaning that the entire line is
meaningful and that continued character constants never
have implicit spaces appended to them to fill out the
line. -ffixed-line-length-0 means the same thing as
-ffixed-line-length-none.
-ffree-line-length-n
Set column after which characters are ignored in typical
free-form lines in the source file. The default value is
132. n may be none, meaning that the entire line is
meaningful. -ffree-line-length-0 means the same thing
as -ffree-line-length-none.
-fmax-identifier-length=n
Specify the maximum allowed identifier length. Typical
values are 31 (Fortran 95) and 63 (Fortran 2003 and
Fortran 2008).
-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.
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-finteger-4-integer-8
Promote all "INTEGER(KIND=4)" entities to an
"INTEGER(KIND=8)" entities. If "KIND=8" is unavailable,
then an error will be issued. This option should be
used with care and may not be suitable for your codes.
Areas of possible concern include calls to external
procedures, alignment in "EQUIVALENCE" and/or "COMMON",
generic interfaces, BOZ literal constant conversion, and
I/O. Inspection of the intermediate representation of
the translated Fortran code, produced by
-fdump-tree-original, is suggested.
-fcray-pointer
Enable the Cray pointer extension, which provides C-like
pointer functionality.
-fopenmp
Enable the OpenMP extensions. This includes OpenMP
"!$omp" directives in free form and "c$omp", *$omp and
"!$omp" directives in fixed form, "!$" conditional
compilation sentinels in free form and "c$", "*$" and
"!$" sentinels in fixed form, and when linking arranges
for the OpenMP runtime library to be linked in. The
option -fopenmp implies -frecursive.
-fno-range-check
Disable range checking on results of simplification of
constant expressions during compilation. For example,
GNU Fortran will give an error at compile time when
simplifying "a = 1. / 0". With this option, no error
will be given and "a" will be assigned the value
"+Infinity". If an expression evaluates to a value
outside of the relevant range of ["-HUGE()":"HUGE()"],
then the expression will be replaced by "-Inf" or "+Inf"
as appropriate. Similarly, "DATA i/Z'FFFFFFFF'/" will
result in an integer overflow on most systems, but with
-fno-range-check the value will "wrap around" and "i"
will be initialized to -1 instead.
-freal-4-real-8
-freal-4-real-10
-freal-8-real-4
-freal-8-real-10
-freal-8-real-16
Promote all "REAL(KIND=M)" entities to "REAL(KIND=N)"
entities. If "REAL(KIND=N)" is unavailable, then an
error will be issued. All other real kind types are
unaffected by this option. These options should be used
with care and may not be suitable for your codes. Areas
of possible concern include calls to external
procedures, alignment in "EQUIVALENCE" and/or "COMMON",
generic interfaces, BOZ literal constant conversion, and
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I/O. Inspection of the intermediate representation of
the translated Fortran code, produced by
-fdump-tree-original, is suggested.
-std=std
Specify the standard to which the program is expected to
conform, which may be one of f95, f2003, f2008, gnu, or
legacy. The default value for std is gnu, which
specifies a superset of the Fortran 95 standard that
includes all of the extensions supported by GNU Fortran,
although warnings will be given for obsolete extensions
not recommended for use in new code. The legacy value
is equivalent but without the warnings for obsolete
extensions, and may be useful for old non-standard
programs. The f95, f2003 and f2008 values specify
strict conformance to the Fortran 95, Fortran 2003 and
Fortran 2008 standards, respectively; errors are given
for all extensions beyond the relevant language
standard, and warnings are given for the Fortran 77
features that are permitted but obsolescent in later
standards. -std=f2008ts allows the Fortran 2008 standard
including the additions of the Technical Specification
(TS) 29113 on Further Interoperability of Fortran with
C.
Enable and customize preprocessing
Preprocessor related options. See section Preprocessing and
conditional compilation for more detailed information on
preprocessing in gfortran.
-cpp
-nocpp
Enable preprocessing. The preprocessor is automatically
invoked if the file extension is .fpp, .FPP, .F, .FOR,
.FTN, .F90, .F95, .F03 or .F08. Use this option to
manually enable preprocessing of any kind of Fortran
file.
To disable preprocessing of files with any of the above
listed extensions, use the negative form: -nocpp.
The preprocessor is run in traditional mode. Any
restrictions of the file-format, especially the limits
on line length, apply for preprocessed output as well,
so it might be advisable to use the
-ffree-line-length-none or -ffixed-line-length-none
options.
-dM Instead of the normal output, generate a list of
'#define' directives for all the macros defined during
the execution of the preprocessor, including predefined
macros. This gives you a way of finding out what is
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predefined in your version of the preprocessor.
Assuming you have no file foo.f90, the command
touch foo.f90; gfortran -cpp -E -dM foo.f90
will show all the predefined macros.
-dD Like -dM except in two respects: it does not include the
predefined macros, and it outputs both the "#define"
directives and the result of preprocessing. Both kinds
of output go to the standard output file.
-dN Like -dD, but emit only the macro names, not their
expansions.
-dU Like dD except that only macros that are expanded, or
whose definedness is tested in preprocessor directives,
are output; the output is delayed until the use or test
of the macro; and '#undef' directives are also output
for macros tested but undefined at the time.
-dI Output '#include' directives in addition to the result
of preprocessing.
-fworking-directory
Enable generation of linemarkers in the preprocessor
output that will let the compiler know the current
working directory at the time of preprocessing. When
this option is enabled, the preprocessor will emit,
after the initial linemarker, a second linemarker with
the current working directory followed by two slashes.
GCC will use this directory, when it is present in the
preprocessed input, as the directory emitted as the
current working directory in some debugging information
formats. This option is implicitly enabled if debugging
information is enabled, but this can be inhibited with
the negated form -fno-working-directory. If the -P flag
is present in the command line, this option has no
effect, since no "#line" directives are emitted
whatsoever.
-idirafter dir
Search dir for include files, but do it after all
directories specified with -I and the standard system
directories have been exhausted. dir is treated as a
system include directory. If dir begins with "=", then
the "=" will be replaced by the sysroot prefix; see
--sysroot and -isysroot.
-imultilib dir
Use dir as a subdirectory of the directory containing
target-specific C++ headers.
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-iprefix prefix
Specify prefix as the prefix for subsequent -iwithprefix
options. If the prefix represents a directory, you
should include the final '/'.
-isysroot dir
This option is like the --sysroot option, but applies
only to header files. See the --sysroot option for more
information.
-iquote dir
Search dir only for header files requested with
"#include "file""; they are not searched for "#include
<file>", before all directories specified by -I and
before the standard system directories. If dir begins
with "=", then the "=" will be replaced by the sysroot
prefix; see --sysroot and -isysroot.
-isystem dir
Search dir for header files, after all directories
specified by -I but before the standard system
directories. Mark it as a system directory, so that it
gets the same special treatment as is applied to the
standard system directories. If dir begins with "=",
then the "=" will be replaced by the sysroot prefix; see
--sysroot and -isysroot.
-nostdinc
Do not search the standard system directories for header
files. Only the directories you have specified with -I
options (and the directory of the current file, if
appropriate) are searched.
-undef
Do not predefine any system-specific or GCC-specific
macros. The standard predefined macros remain defined.
-Apredicate=answer
Make an assertion with the predicate predicate and
answer answer. This form is preferred to the older form
-A predicate(answer), which is still supported, because
it does not use shell special characters.
-A-predicate=answer
Cancel an assertion with the predicate predicate and
answer answer.
-C Do not discard comments. All comments are passed through
to the output file, except for comments in processed
directives, which are deleted along with the directive.
You should be prepared for side effects when using -C;
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it causes the preprocessor to treat comments as tokens
in their own right. For example, comments appearing at
the start of what would be a directive line have the
effect of turning that line into an ordinary source
line, since the first token on the line is no longer a
'#'.
Warning: this currently handles C-Style comments only.
The preprocessor does not yet recognize Fortran-style
comments.
-CC Do not discard comments, including during macro
expansion. This is like -C, except that comments
contained within macros are also passed through to the
output file where the macro is expanded.
In addition to the side-effects of the -C option, the
-CC option causes all C++-style comments inside a macro
to be converted to C-style comments. This is to prevent
later use of that macro from inadvertently commenting
out the remainder of the source line. The -CC option is
generally used to support lint comments.
Warning: this currently handles C- and C++-Style
comments only. The preprocessor does not yet recognize
Fortran-style comments.
-Dname
Predefine name as a macro, with definition 1.
-Dname=definition
The contents of definition are tokenized and processed
as if they appeared during translation phase three in a
'#define' directive. In particular, the definition will
be truncated by embedded newline characters.
If you are invoking the preprocessor from a shell or
shell-like program you may need to use the shell's
quoting syntax to protect characters such as spaces that
have a meaning in the shell syntax.
If you wish to define a function-like macro on the
command line, write its argument list with surrounding
parentheses before the equals sign (if any). Parentheses
are meaningful to most shells, so you will need to quote
the option. With sh and csh,
"-D'name(args...)=definition'" works.
-D and -U options are processed in the order they are
given on the command line. All -imacros file and
-include file options are processed after all -D and -U
options.
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-H Print the name of each header file used, in addition to
other normal activities. Each name is indented to show
how deep in the '#include' stack it is.
-P Inhibit generation of linemarkers in the output from the
preprocessor. This might be useful when running the
preprocessor on something that is not C code, and will
be sent to a program which might be confused by the
linemarkers.
-Uname
Cancel any previous definition of name, either built in
or provided with a -D option.
Options to request or suppress errors and warnings
Errors are diagnostic messages that report that the GNU
Fortran compiler cannot compile the relevant piece of source
code. The compiler will continue to process the program in
an attempt to report further errors to aid in debugging, but
will not produce any compiled output.
Warnings are diagnostic messages that report constructions
which are not inherently erroneous but which are risky or
suggest there is likely to be a bug in the program. Unless
-Werror is specified, they do not prevent compilation of the
program.
You can request many specific warnings with options
beginning -W, for example -Wimplicit to request warnings on
implicit declarations. Each of these specific warning
options also has a negative form beginning -Wno- to turn off
warnings; for example, -Wno-implicit. This manual lists
only one of the two forms, whichever is not the default.
These options control the amount and kinds of errors and
warnings produced by GNU Fortran:
-fmax-errors=n
Limits the maximum number of error messages to n, at
which point GNU Fortran bails out rather than attempting
to continue processing the source code. If n is 0,
there is no limit on the number of error messages
produced.
-fsyntax-only
Check the code for syntax errors, but do not actually
compile it. This will generate module files for each
module present in the code, but no other output file.
-pedantic
Issue warnings for uses of extensions to Fortran 95.
-pedantic also applies to C-language constructs where
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they occur in GNU Fortran source files, such as use of
\e in a character constant within a directive like
"#include".
Valid Fortran 95 programs should compile properly with
or without this option. However, without this option,
certain GNU extensions and traditional Fortran features
are supported as well. With this option, many of them
are rejected.
Some users try to use -pedantic to check programs for
conformance. They soon find that it does not do quite
what they want---it finds some nonstandard practices,
but not all. However, improvements to GNU Fortran in
this area are welcome.
This should be used in conjunction with -std=f95,
-std=f2003 or -std=f2008.
-pedantic-errors
Like -pedantic, except that errors are produced rather
than warnings.
-Wall
Enables commonly used warning options pertaining to
usage that we recommend avoiding and that we believe are
easy to avoid. This currently includes -Waliasing,
-Wampersand, -Wconversion, -Wsurprising,
-Wc-binding-type, -Wintrinsics-std, -Wno-tabs,
-Wintrinsic-shadow, -Wline-truncation,
-Wtarget-lifetime, -Wreal-q-constant and -Wunused.
-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
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Warn about missing ampersand in continued character
constants. The warning is given with -Wampersand,
-pedantic, -std=f95, -std=f2003 and -std=f2008. 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.
-Warray-temporaries
Warn about array temporaries generated by the compiler.
The information generated by this warning is sometimes
useful in optimization, in order to avoid such
temporaries.
-Wc-binding-type
Warn if the a variable might not be C interoperable. In
particular, warn if the variable has been declared using
an intrinsic type with default kind instead of using a
kind parameter defined for C interoperability in the
intrinsic "ISO_C_Binding" module. This option is
implied by -Wall.
-Wcharacter-truncation
Warn when a character assignment will truncate the
assigned string.
-Wline-truncation
Warn when a source code line will be truncated. This
option is implied by -Wall.
-Wconversion
Warn about implicit conversions that are likely to
change the value of the expression after conversion.
Implied by -Wall.
-Wconversion-extra
Warn about implicit conversions between different types
and kinds.
-Wextra
Enables some warning options for usages of language
features which may be problematic. This currently
includes -Wcompare-reals and -Wunused-parameter.
-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.
-Wimplicit-procedure
Warn if a procedure is called that has neither an
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explicit interface nor has been declared as "EXTERNAL".
-Wintrinsics-std
Warn if gfortran finds a procedure named like an
intrinsic not available in the currently selected
standard (with -std) and treats it as "EXTERNAL"
procedure because of this. -fall-intrinsics can be used
to never trigger this behavior and always link to the
intrinsic regardless of the selected standard.
-Wreal-q-constant
Produce a warning if a real-literal-constant contains a
"q" exponent-letter.
-Wsurprising
Produce a warning when "suspicious" code constructs are
encountered. While technically legal these usually
indicate that an error has been made.
This currently produces a warning under the following
circumstances:
o An INTEGER SELECT construct has a CASE that can
never be matched as its lower value is greater than
its upper value.
o A LOGICAL SELECT construct has three CASE
statements.
o A TRANSFER specifies a source that is shorter than
the destination.
o The type of a function result is declared more than
once with the same type. If -pedantic or standard-
conforming mode is enabled, this is an error.
o A "CHARACTER" variable is declared with negative
length.
-Wtabs
By default, tabs are accepted as whitespace, but tabs
are not members of the Fortran Character Set. For
continuation lines, a tab followed by a digit between 1
and 9 is supported. -Wno-tabs will cause a warning to
be issued if a tab is encountered. Note, -Wno-tabs is
active for -pedantic, -std=f95, -std=f2003, -std=f2008
and -Wall.
-Wunderflow
Produce a warning when numerical constant expressions
are encountered, which yield an UNDERFLOW during
compilation.
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-Wintrinsic-shadow
Warn if a user-defined procedure or module procedure has
the same name as an intrinsic; in this case, an explicit
interface or "EXTERNAL" or "INTRINSIC" declaration might
be needed to get calls later resolved to the desired
intrinsic/procedure. This option is implied by -Wall.
-Wunused-dummy-argument
Warn about unused dummy arguments. This option is
implied by -Wall.
-Wunused-parameter
Contrary to gcc's meaning of -Wunused-parameter,
gfortran's implementation of this option does not warn
about unused dummy arguments (see
-Wunused-dummy-argument), but about unused "PARAMETER"
values. -Wunused-parameter is not included in -Wall but
is implied by -Wall -Wextra.
-Walign-commons
By default, gfortran warns about any occasion of
variables being padded for proper alignment inside a
"COMMON" block. This warning can be turned off via
-Wno-align-commons. See also -falign-commons.
-Wfunction-elimination
Warn if any calls to functions are eliminated by the
optimizations enabled by the -ffrontend-optimize option.
-Wrealloc-lhs
Warn when the compiler might insert code to for
allocation or reallocation of an allocatable array
variable of intrinsic type in intrinsic assignments. In
hot loops, the Fortran 2003 reallocation feature may
reduce the performance. If the array is already
allocated with the correct shape, consider using a
whole-array array-spec (e.g. "(:,:,:)") for the variable
on the left-hand side to prevent the reallocation check.
Note that in some cases the warning is shown, even if
the compiler will optimize reallocation checks away.
For instance, when the right-hand side contains the same
variable multiplied by a scalar. See also
-frealloc-lhs.
-Wrealloc-lhs-all
Warn when the compiler inserts code to for allocation or
reallocation of an allocatable variable; this includes
scalars and derived types.
-Wcompare-reals
Warn when comparing real or complex types for equality
or inequality. This option is implied by -Wextra.
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GNU GFORTRAN(1)
-Wtarget-lifetime
Warn if the pointer in a pointer assignment might be
longer than the its target. This option is implied by
-Wall.
-Werror
Turns all warnings into errors.
Some of these have no effect when compiling programs written
in Fortran.
Options for debugging your program or GNU Fortran
GNU Fortran has various special options that are used for
debugging either your program or the GNU Fortran compiler.
-fdump-fortran-original
Output the internal parse tree after translating the
source program into internal representation. Only
really useful for debugging the GNU Fortran compiler
itself.
-fdump-optimized-tree
Output the parse tree after front-end optimization.
Only really useful for debugging the GNU Fortran
compiler itself.
Output the internal parse tree after translating the
source program into internal representation. Only
really useful for debugging the GNU Fortran compiler
itself. This option is deprecated; use
"-fdump-fortran-original" instead.
-ffpe-trap=list
Specify a list of floating point exception traps to
enable. On most systems, if a floating point exception
occurs and the trap for that exception is enabled, a
SIGFPE signal will be sent and the program being
aborted, producing a core file useful for debugging.
list is a (possibly empty) comma-separated list of the
following 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), inexact (loss of precision during
operation), and denormal (operation performed on a
denormal value). The first five exceptions correspond
to the five IEEE 754 exceptions, whereas the last one
(denormal) is not part of the IEEE 754 standard but is
available on some common architectures such as x86.
The first three exceptions (invalid, zero, and overflow)
often indicate serious errors, and unless the program
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has provisions for dealing with these exceptions,
enabling traps for these three exceptions is probably a
good idea.
Many, if not most, floating point operations incur loss
of precision due to rounding, and hence the
"ffpe-trap=inexact" is likely to be uninteresting in
practice.
By default no exception traps are enabled.
-fno-backtrace
When a serious runtime error is encountered or a deadly
signal is emitted (segmentation fault, illegal
instruction, bus error, floating-point exception, and
the other POSIX signals that have the action core), the
Fortran runtime library tries to output a backtrace of
the error. "-fno-backtrace" disables the backtrace
generation. This option only has influence for
compilation of the Fortran main program.
Options for directory search
These options affect how GNU Fortran searches for files
specified by the "INCLUDE" directive and where it searches
for previously compiled modules.
It also affects the search paths used by cpp when used to
preprocess Fortran source.
-Idir
These affect interpretation of the "INCLUDE" directive
(as well as of the "#include" directive of the cpp
preprocessor).
Also note that the general behavior of -I and "INCLUDE"
is pretty much the same as of -I with "#include" in the
cpp preprocessor, with regard to looking for header.gcc
files and other such things.
This path is also used to search for .mod files when
previously compiled modules are required by a "USE"
statement.
-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.
-fintrinsic-modules-path dir
This option specifies the location of pre-compiled
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intrinsic modules, if they are not in the default
location expected by the compiler.
Influencing the linking step
These options come into play when the compiler links object
files into an executable output file. They are meaningless
if the compiler is not doing a link step.
-static-libgfortran
On systems that provide libgfortran as a shared and a
static library, this option forces the use of the static
version. If no shared version of libgfortran was built
when the compiler was configured, this option has no
effect.
Influencing runtime behavior
These options affect the runtime behavior of programs
compiled with GNU Fortran.
-fconvert=conversion
Specify the representation of data for unformatted
files. Valid values for conversion are: native, the
default; swap, swap between big- and little-endian; big-
endian, use big-endian representation for unformatted
files; little-endian, use little-endian representation
for unformatted files.
This option has an effect only when used in the main
program. The "CONVERT" specifier and the
GFORTRAN_CONVERT_UNIT environment variable override the
default specified by -fconvert.
-frecord-marker=length
Specify the length of record markers for unformatted
files. Valid values for length are 4 and 8. Default is
4. This is different from previous versions of
gfortran, which specified a default record marker length
of 8 on most systems. If you want to read or write
files compatible with earlier versions of gfortran, use
-frecord-marker=8.
-fmax-subrecord-length=length
Specify the maximum length for a subrecord. The maximum
permitted value for length is 2147483639, which is also
the default. Only really useful for use by the gfortran
testsuite.
-fsign-zero
When enabled, floating point numbers of value zero with
the sign bit set are written as negative number in
formatted output and treated as negative in the "SIGN"
intrinsic. -fno-sign-zero does not print the negative
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sign of zero values (or values rounded to zero for I/O)
and regards zero as positive number in the "SIGN"
intrinsic for compatibility with Fortran 77. The default
is -fsign-zero.
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 (except those marked as
RECURSIVE) as if the "SAVE" statement were 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 or -save.)
The default, which is -fautomatic, uses the stack for
local variables smaller than the value given by
-fmax-stack-var-size. Use the option -frecursive to use
no static memory.
-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
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break at execution time.
Caution: This will break code which passes intrinsic
functions of type default "REAL" or "COMPLEX" as actual
arguments, as the library implementations use the
-fno-f2c calling conventions.
-fno-underscoring
Do not transform names of entities specified in the
Fortran source file by appending underscores to them.
With -funderscoring in effect, GNU Fortran appends one
underscore to external names with no underscores. This
is done to ensure compatibility with code produced by
many UNIX Fortran compilers.
Caution: The default behavior of GNU Fortran is
incompatible with f2c and g77, please use the -ff2c
option if you want object files compiled with GNU
Fortran to be compatible with object code created with
these tools.
Use of -fno-underscoring is not recommended unless you
are experimenting with issues such as integration of GNU
Fortran into existing system environments (vis-a-vis
existing libraries, tools, and so on).
For example, with -funderscoring, and assuming other
defaults like -fcase-lower and that "j()" and
"max_count()" are external functions while "my_var" and
"lvar" are local variables, a statement like
I = J() + MAX_COUNT (MY_VAR, LVAR)
is implemented as something akin to:
i = j_() + max_count__(&my_var__, &lvar);
With -fno-underscoring, the same statement is
implemented as:
i = j() + max_count(&my_var, &lvar);
Use of -fno-underscoring allows direct specification of
user-defined names while debugging and when interfacing
GNU Fortran code with other languages.
Note that just because the names match does not mean
that the interface implemented by GNU Fortran for an
external name matches the interface implemented by some
other language for that same name. That is, getting
code produced by GNU Fortran to link to code produced by
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GNU GFORTRAN(1)
some other compiler using this or any other method can
be only a small part of the overall solution---getting
the code generated by both compilers to agree on issues
other than naming can require significant effort, and,
unlike naming disagreements, linkers normally cannot
detect disagreements in these other areas.
Also, note that with -fno-underscoring, the lack of
appended underscores introduces the very real
possibility that a user-defined external name will
conflict with a name in a system library, which could
make finding unresolved-reference bugs quite difficult
in some cases---they might occur at program run time,
and show up only as buggy behavior at run time.
In future versions of GNU Fortran we hope to improve
naming and linking issues so that debugging always
involves using the names as they appear in the source,
even if the names as seen by the linker are mangled to
prevent accidental linking between procedures with
incompatible interfaces.
-fno-whole-file
This flag causes the compiler to resolve and translate
each procedure in a file separately.
By default, the whole file is parsed and placed in a
single front-end tree. During resolution, in addition
to all the usual checks and fixups, references to
external procedures that are in the same file effect
resolution of that procedure, if not already done, and a
check of the interfaces. The dependences are resolved
by changing the order in which the file is translated
into the backend tree. Thus, a procedure that is
referenced is translated before the reference and the
duplication of backend tree declarations eliminated.
The -fno-whole-file option is deprecated and may lead to
wrong code.
-fsecond-underscore
By default, GNU Fortran appends an underscore to
external names. If this option is used GNU Fortran
appends two underscores to names with underscores and
one underscore to external names with no underscores.
GNU Fortran also appends two underscores to internal
names with underscores to avoid naming collisions with
external names.
This option has no effect if -fno-underscoring is in
effect. It is implied by the -ff2c option.
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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.
-fcoarray=<keyword>
none
Disable coarray support; using coarray declarations
and image-control statements will produce a compile-
time error. (Default)
single
Single-image mode, i.e. "num_images()" is always
one.
lib Library-based coarray parallelization; a suitable
GNU Fortran coarray library needs to be linked.
-fcheck=<keyword>
Enable the generation of run-time checks; the argument
shall be a comma-delimited list of the following
keywords.
all Enable all run-time test of -fcheck.
array-temps
Warns at run time when for passing an actual
argument a temporary array had to be generated. The
information generated by this warning is sometimes
useful in optimization, in order to avoid such
temporaries.
Note: The warning is only printed once per location.
bounds
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 and ensures that all string lengths
are equal for character array constructors without
an explicit typespec.
Some checks require that -fcheck=bounds is set for
the compilation of the main program.
Note: In the future this may also include other
forms of checking, e.g., checking substring
references.
do Enable generation of run-time checks for invalid
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modification of loop iteration variables.
mem Enable generation of run-time checks for memory
allocation. Note: This option does not affect
explicit allocations using the "ALLOCATE" statement,
which will be always checked.
pointer
Enable generation of run-time checks for pointers
and allocatables.
recursion
Enable generation of run-time checks for recursively
called subroutines and functions which are not
marked as recursive. See also -frecursive. Note:
This check does not work for OpenMP programs and is
disabled if used together with -frecursive and
-fopenmp.
-fbounds-check
Deprecated alias for -fcheck=bounds.
-fcheck-array-temporaries
Deprecated alias for -fcheck=array-temps.
-fmax-array-constructor=n
This option can be used to increase the upper limit
permitted in array constructors. The code below
requires this option to expand the array at compile
time.
program test
implicit none
integer j
integer, parameter :: n = 100000
integer, parameter :: i(n) = (/ (2*j, j = 1, n) /)
print '(10(I0,1X))', i
end program test
Caution: This option can lead to long compile times and
excessively large object files.
The default value for n is 65535.
-fmax-stack-var-size=n
This option specifies the size in bytes of the largest
array that will be put on the stack; if the size is
exceeded static memory is used (except in procedures
marked as RECURSIVE). Use the option -frecursive to
allow for recursive procedures which do not have a
RECURSIVE attribute or for parallel programs. Use
-fno-automatic to never use the stack.
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This option currently only affects local arrays declared
with constant bounds, and may not apply to all character
variables. Future versions of GNU Fortran may improve
this behavior.
The default value for n is 32768.
-fstack-arrays
Adding this option will make the Fortran compiler put
all local arrays, even those of unknown size onto stack
memory. If your program uses very large local arrays it
is possible that you will have to extend your runtime
limits for stack memory on some operating systems. This
flag is enabled by default at optimization level -Ofast.
-fpack-derived
This option tells GNU Fortran to pack derived type
members as closely as possible. Code compiled with this
option is likely to be incompatible with code compiled
without this option, and may execute slower.
-frepack-arrays
In some circumstances GNU Fortran may pass assumed shape
array sections via a descriptor describing a
noncontiguous area of memory. This option adds code to
the function prologue to repack the data into a
contiguous block at runtime.
This should result in faster accesses to the array.
However it can introduce significant overhead to the
function call, especially when the passed data is
noncontiguous.
-fshort-enums
This option is provided for interoperability with C code
that was compiled with the -fshort-enums option. It
will make GNU Fortran choose the smallest "INTEGER" kind
a given enumerator set will fit in, and give all its
enumerators this kind.
-fexternal-blas
This option will make gfortran generate calls to BLAS
functions for some matrix operations like "MATMUL",
instead of using our own algorithms, if the size of the
matrices involved is larger than a given limit (see
-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.
-fblas-matmul-limit=n
Only significant when -fexternal-blas is in effect.
Matrix multiplication of matrices with size larger than
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(or equal to) n will be performed by calls to BLAS
functions, while others will be handled by 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 n is 30.
-frecursive
Allow indirect recursion by forcing all local arrays to
be allocated on the stack. This flag cannot be used
together with -fmax-stack-var-size= or -fno-automatic.
-finit-local-zero
-finit-integer=n
-finit-real=<zero|inf|-inf|nan|snan>
-finit-logical=<true|false>
-finit-character=n
The -finit-local-zero option instructs the compiler to
initialize local "INTEGER", "REAL", and "COMPLEX"
variables to zero, "LOGICAL" variables to false, and
"CHARACTER" variables to a string of null bytes. Finer-
grained initialization options are provided by the
-finit-integer=n, -finit-real=<zero|inf|-inf|nan|snan>
(which also initializes the real and imaginary parts of
local "COMPLEX" variables), -finit-logical=<true|false>,
and -finit-character=n (where n is an ASCII character
value) options. These options do not initialize
o allocatable arrays
o components of derived type variables
o variables that appear in an "EQUIVALENCE" statement.
(These limitations may be removed in future releases).
Note that the -finit-real=nan option initializes "REAL"
and "COMPLEX" variables with a quiet NaN. For a
signalling NaN use -finit-real=snan; note, however, that
compile-time optimizations may convert them into quiet
NaN and that trapping needs to be enabled (e.g. via
-ffpe-trap).
Finally, note that enabling any of the -finit-* options
will silence warnings that would have been emitted by
-Wuninitialized for the affected local variables.
-falign-commons
By default, gfortran enforces proper alignment of all
variables in a "COMMON" block by padding them as needed.
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GNU GFORTRAN(1)
On certain platforms this is mandatory, on others it
increases performance. If a "COMMON" block is not
declared with consistent data types everywhere, this
padding can cause trouble, and -fno-align-commons can be
used to disable automatic alignment. The same form of
this option should be used for all files that share a
"COMMON" block. To avoid potential alignment issues in
"COMMON" blocks, it is recommended to order objects from
largest to smallest.
-fno-protect-parens
By default the parentheses in expression are honored for
all optimization levels such that the compiler does not
do any re-association. Using -fno-protect-parens allows
the compiler to reorder "REAL" and "COMPLEX" expressions
to produce faster code. Note that for the re-association
optimization -fno-signed-zeros and -fno-trapping-math
need to be in effect. The parentheses protection is
enabled by default, unless -Ofast is given.
-frealloc-lhs
An allocatable left-hand side of an intrinsic assignment
is automatically (re)allocated if it is either
unallocated or has a different shape. The option is
enabled by default except when -std=f95 is given. See
also -Wrealloc-lhs.
-faggressive-function-elimination
Functions with identical argument lists are eliminated
within statements, regardless of whether these functions
are marked "PURE" or not. For example, in
a = f(b,c) + f(b,c)
there will only be a single call to "f". This option
only works if -ffrontend-optimize is in effect.
-ffrontend-optimize
This option performs front-end optimization, based on
manipulating parts the Fortran parse tree. Enabled by
default by any -O option. Optimizations enabled by this
option include elimination of identical function calls
within expressions, removing unnecessary calls to "TRIM"
in comparisons and assignments and replacing TRIM(a)
with "a(1:LEN_TRIM(a))". It can be deselected by
specifying -fno-frontend-optimize.
ENVIRONMENT
The gfortran compiler currently does not make use of any
environment variables to control its operation above and
beyond those that affect the operation of gcc.
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GNU GFORTRAN(1)
BUGS
For instructions on reporting bugs, see
<http://gcc.gnu.org/bugs.html>.
ATTRIBUTES
See attributes(5) for descriptions of the following
attributes:
+---------------+---------------------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+---------------------------------+
|Availability | developer/gcc-4/gcc-gfortran-48 |
+---------------+---------------------------------+
|Stability | Uncommitted |
+---------------+---------------------------------+
SEE ALSO
gpl(7), gfdl(7), fsf-funding(7), cpp(1), gcov(1), gcc(1),
as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1) and the Info
entries for gcc, cpp, gfortran, as, ld, binutils and gdb.
AUTHOR
See the Info entry for gfortran for contributors to GCC and
GNU Fortran.
COPYRIGHT
Copyright (c) 2004-2013 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 1.3 or any later version published by the
Free Software Foundation; with the Invariant Sections being
"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.
NOTES
This software was built from source available at
https://java.net/projects/solaris-userland. The original
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GNU GFORTRAN(1)
community source was downloaded from
http://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.gz
Further information about this software can be found on the
open source community website at http://gcc.gnu.org/.
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