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GFORTRAN(1)                           GNU                          GFORTRAN(1)



NAME
       gfortran - GNU Fortran compiler

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

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

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

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

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

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

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

       Preprocessing Options
           -cpp -dD -dI -dM -dN -dU -fworking-directory -imultilib dir -iprefix file -isysroot dir -iquote -isystem
           dir -nocpp -nostdinc -undef -Aquestion=answer -A-question[=answer] -C -CC -Dmacro[=defn] -Umacro -H -P

       Error and Warning Options
           -fmax-errors=n -fsyntax-only  -pedantic  -pedantic-errors -Wall  -Waliasing  -Wampersand  -Warray-bounds
           -Wcharacter-truncation -Wconversion -Wimplicit-interface  -Wline-truncation  -Wintrinsics-std -Wsurprising
           -Wno-tabs  -Wunderflow -Wunused-parameter -Wintrinsics-shadow -Wno-align-commons

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

       Directory Options
           -Idir  -Jdir -fintrinsic-modules-path dir

       Link Options
           -static-libgfortran

       Runtime Options
           -fconvert=conversion  -fno-range-check -frecord-marker=length   -fmax-subrecord-length=length -fsign-zero

       Code Generation Options
           -fno-automatic  -ff2c  -fno-underscoring -fsecond-underscore -fbounds-check -fcheck-array-temporaries
           -fmax-array-constructor =n -fmax-stack-var-size=n -fpack-derived  -frepack-arrays  -fshort-enums
           -fexternal-blas -fblas-matmul-limit=n -frecursive -finit-local-zero -finit-integer=n
           -finit-real=<zero|inf|-inf|nan> -finit-logical=<true|false> -finit-character=n -fno-align-commons

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

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

       -fall-intrinsics
           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 character in a symbol name.

       -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.

       -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.

       -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.

   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, be aware that any restrictions of the file-format, e.g. fixed-
           form line width, apply for preprocessed output as well.

       -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
           predefined in your version of the preprocessor.  Assuming you have no file foo.f90, the command

                     touch foo.f90; gfortran -cpp -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's 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.

       -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; 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.

       -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 don't 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
           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, -Wsurprising, -Wintrinsics-std,
           -Wno-tabs, -Wintrinsic-shadow and -Wline-truncation.

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

           The following example will trigger the warning.

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

                     call bar(a,a)

       -Wampersand
           Warn about missing ampersand in continued character constants. The warning is given with -Wampersand,
           -pedantic, -std=f95, -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.

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

       -Wline-truncation
           Warn when a source code line will be truncated.

       -Wconversion
           Warn about implicit conversions between different types.

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

       -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 behaviour and always link to the intrinsic regardless of the selected standard.

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

           This currently produces a warning under the following circumstances:

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

           ?   A LOGICAL SELECT construct has three CASE statements.

           ?   A TRANSFER specifies a source that is shorter than the destination.

           ?   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.

       -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.

       -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.

       -Wunused-parameter
           Contrary to gcc's meaning of -Wunused-parameter, gfortran's implementation of this option does not warn
           about unused dummy arguments, 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.

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

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

           Some of the routines in the Fortran runtime library, like CPU_TIME, are likely to trigger floating point
           exceptions when "ffpe-trap=precision" is used. For this reason, the use of "ffpe-trap=precision" is not
           recommended.

       -fbacktrace
           Specify that, when a runtime error is encountered or a deadly signal is emitted (segmentation fault,
           illegal instruction, bus error or floating-point exception), the Fortran runtime library should output a
           backtrace of the error.  This option only has influence for compilation of the Fortran main program.

       -fdump-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.

   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 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.

       -fno-range-check
           Disable range checking of input values during integer "READ" operations.  For example, GNU Fortran will
           give an error if an input value is outside of the relevant range of ["-HUGE()":"HUGE()"]. In other words,
           with "INTEGER (kind=4) :: i" , attempting to read -2147483648 will give an error unless -fno-range-check is
           given.

       -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 writing zero values, show the negative sign if the sign bit is set.  "fno-sign-zero" does not print
           the negative sign of zero values for compatibility with F77.  Default behavior is to show the negative
           sign.

   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 break at execution time.

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

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

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

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

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

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

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

           is implemented as something akin to:

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

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

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

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

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

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

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

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

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

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

       -fbounds-check
           Enable generation of run-time checks for array subscripts and against the declared minimum and maximum
           values.  It also checks array indices for assumed and deferred shape arrays against the actual allocated
           bounds and ensures that all string lengths are equal for character array constructors without an explicit
           typespec.

           Some checks require that -fbounds-check 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.

       fcheck-array-temporaries
           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.

       -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.

                   C<program test>
                   C<implicit none>
                   C<integer j>
                   C<integer, parameter :: n = 100000>
                   C<integer, parameter :: i(n) = (/ (2*j, j = 1, n) /)>
                   C<print '(10(I0,1X))', i>
                   C<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.

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

           The default value for n is 32768.

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

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

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

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

       -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 (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>
       -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>
           (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 components of derived type variables, nor do they initialize variables that
           appear in an "EQUIVALENCE" statement.  (This limitation may be removed in future releases).

           Note that the -finit-real=nan option initializes "REAL" and "COMPLEX" variables with a quiet NaN.

       -falign-commons
           By default, gfortran enforces proper alignment of all variables in a COMMON block by padding them as
           needed. 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 largests to smallest.

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

BUGS
       For instructions on reporting bugs, see <http://bugzilla.redhat.com/bugzilla>.

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

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

COPYRIGHT
       Copyright (c) 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.

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

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

            A GNU Manual

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

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



gcc-4.4.7                         2012-03-13                       GFORTRAN(1)