gfortran(1) — Linux manual page

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GFORTRAN(1)                        GNU                       GFORTRAN(1)

NAME         top

       gfortran - GNU Fortran compiler

SYNOPSIS         top

       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         top

       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         top

       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 -fdec -fdec-structure
           -fdec-intrinsic-ints -fdec-static -fdec-math -fdec-include
           -fdefault-double-8 -fdefault-integer-8 -fdefault-real-8
           -fdefault-real-10 -fdefault-real-16 -fdollar-ok
           -ffixed-line-length-n -ffixed-line-length-none -fpad-source
           -ffree-form -ffree-line-length-n -ffree-line-length-none
           -fimplicit-none -finteger-4-integer-8 -fmax-identifier-length
           -fmodule-private -ffixed-form -fno-range-check -fopenacc
           -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
           -ftest-forall-temp

       Preprocessing Options
           -A-question[=answer] -Aquestion=answer -C -CC -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 -Wargument-mismatch
           -Warray-bounds -Wc-binding-type -Wcharacter-truncation
           -Wconversion -Wdo-subscript -Wfunction-elimination
           -Wimplicit-interface -Wimplicit-procedure -Wintrinsic-shadow
           -Wuse-without-only -Wintrinsics-std -Wline-truncation
           -Wno-align-commons -Wno-tabs -Wreal-q-constant -Wsurprising
           -Wunderflow -Wunused-parameter -Wrealloc-lhs
           -Wrealloc-lhs-all -Wfrontend-loop-interchange
           -Wtarget-lifetime -fmax-errors=n -fsyntax-only -pedantic
           -pedantic-errors

       Debugging Options
           -fbacktrace -fdump-fortran-optimized -fdump-fortran-original
           -fdump-fortran-global -fdump-parse-tree -ffpe-trap=list
           -ffpe-summary=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

       Interoperability Options
           -fc-prototypes -fc-prototypes-external

       Code Generation Options
           -faggressive-function-elimination -fblas-matmul-limit=n
           -fbounds-check -ftail-call-workaround
           -ftail-call-workaround=n -fcheck-array-temporaries
           -fcheck=<all|array-temps|bounds|do|mem|pointer|recursion>
           -fcoarray=<none|single|lib> -fexternal-blas -ff2c
           -ffrontend-loop-interchange -ffrontend-optimize
           -finit-character=n -finit-integer=n -finit-local-zero
           -finit-derived -finit-logical=<true|false>
           -finit-real=<zero|inf|-inf|nan|snan> -finline-matmul-limit=n
           -fmax-array-constructor=n -fmax-stack-var-size=n
           -fno-align-commons -fno-automatic -fno-protect-parens
           -fno-underscoring -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 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.

       -fdec
           DEC compatibility mode. Enables extensions and other features
           that mimic the default behavior of older compilers (such as
           DEC).  These features are non-standard and should be avoided
           at all costs.  For details on GNU Fortran's implementation of
           these extensions see the full documentation.

           Other flags enabled by this switch are: -fdollar-ok
           -fcray-pointer -fdec-structure -fdec-intrinsic-ints
           -fdec-static -fdec-math

           If -fd-lines-as-code/-fd-lines-as-comments are unset, then
           -fdec also sets -fd-lines-as-comments.

       -fdec-structure
           Enable DEC "STRUCTURE" and "RECORD" as well as "UNION",
           "MAP", and dot ('.') as a member separator (in addition to
           '%'). This is provided for compatibility only; Fortran 90
           derived types should be used instead where possible.

       -fdec-intrinsic-ints
           Enable B/I/J/K kind variants of existing integer functions
           (e.g. BIAND, IIAND, JIAND, etc...). For a complete list of
           intrinsics see the full documentation.

       -fdec-math
           Enable legacy math intrinsics such as COTAN and degree-valued
           trigonometric functions (e.g. TAND, ATAND, etc...) for
           compatability with older code.

       -fdec-static
           Enable DEC-style STATIC and AUTOMATIC attributes to
           explicitly specify the storage of variables and other
           objects.

       -fdec-include
           Enable parsing of INCLUDE as a statement in addition to
           parsing it as INCLUDE line.  When parsed as INCLUDE
           statement, INCLUDE does not have to be on a single line and
           can use line continuations.

       -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.

       -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, unless
           "-fno-pad-source", 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.

       -fno-pad-source
           By default fixed-form lines have spaces assumed (as if padded
           to that length) after the ends of short fixed-form lines.
           This is not done either if -ffixed-line-length-0,
           -ffixed-line-length-none or if -fno-pad-source option is
           used.  With any of those options continued character
           constants never have implicit spaces appended to them to fill
           out the line.

       -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.

       -fopenacc
           Enable the OpenACC extensions.  This includes OpenACC "!$acc"
           directives in free form and "c$acc", *$acc and "!$acc"
           directives in fixed form, "!$" conditional compilation
           sentinels in free form and "c$", "*$" and "!$" sentinels in
           fixed form, and when linking arranges for the OpenACC runtime
           library to be linked in.

           Note that this is an experimental feature, incomplete, and
           subject to change in future versions of GCC.  See
           <https://gcc.gnu.org/wiki/OpenACC > for more information.

       -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.

       -fdefault-integer-8
           Set the default integer and logical types to an 8 byte wide
           type.  This option also affects the kind of integer constants
           like 42. Unlike -finteger-4-integer-8, it does not promote
           variables with explicit kind declaration.

       -fdefault-real-8
           Set the default real type to an 8 byte wide type.  This
           option also affects the kind of non-double real constants
           like 1.0.  This option promotes the default width of "DOUBLE
           PRECISION" and double real constants like "1.d0" to 16 bytes
           if possible.  If "-fdefault-double-8" is given along with
           "fdefault-real-8", "DOUBLE PRECISION" and double real
           constants are not promoted.  Unlike -freal-4-real-8,
           "fdefault-real-8" does not promote variables with explicit
           kind declarations.

       -fdefault-real-10
           Set the default real type to an 10 byte wide type.  This
           option also affects the kind of non-double real constants
           like 1.0.  This option promotes the default width of "DOUBLE
           PRECISION" and double real constants like "1.d0" to 16 bytes
           if possible.  If "-fdefault-double-8" is given along with
           "fdefault-real-10", "DOUBLE PRECISION" and double real
           constants are not promoted.  Unlike -freal-4-real-10,
           "fdefault-real-10" does not promote variables with explicit
           kind declarations.

       -fdefault-real-16
           Set the default real type to an 16 byte wide type.  This
           option also affects the kind of non-double real constants
           like 1.0.  This option promotes the default width of "DOUBLE
           PRECISION" and double real constants like "1.d0" to 16 bytes
           if possible.  If "-fdefault-double-8" is given along with
           "fdefault-real-16", "DOUBLE PRECISION" and double real
           constants are not promoted.  Unlike -freal-4-real-16,
           "fdefault-real-16" does not promote variables with explicit
           kind declarations.

       -fdefault-double-8
           Set the "DOUBLE PRECISION" type and double real constants
           like "1.d0" to an 8 byte wide type.  Do nothing if this is
           already the default.  This option prevents -fdefault-real-8,
           -fdefault-real-10, and -fdefault-real-16, from promoting
           "DOUBLE PRECISION" and double real constants like "1.d0" to
           16 bytes.

       -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.

       -freal-4-real-8
       -freal-4-real-10
       -freal-4-real-16
       -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 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, f2018, gnu,
           or legacy.  The default value for std is gnu, which specifies
           a superset of the latest Fortran 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, f2008, and f2018
           values specify strict conformance to the Fortran 95, Fortran
           2003, Fortran 2008 and Fortran 2018 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. The deprecated option -std=f2008ts acts as an
           alias for -std=f2018. It is only present for backwards
           compatibility with earlier gfortran versions and should not
           be used any more.

       -ftest-forall-temp
           Enhance test coverage by forcing most forall assignments to
           use temporary.

   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 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.

       -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 do not actually compile
           it.  This will generate module files for each module present
           in the code, but no other output file.

       -Wpedantic
       -pedantic
           Issue warnings for uses of extensions to Fortran.  -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 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,
           -std=f2008 or -std=f2018.

       -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, -Wtabs, -Wintrinsic-shadow,
           -Wline-truncation, -Wtarget-lifetime, -Winteger-division,
           -Wreal-q-constant, -Wunused and -Wundefined-do-loop.

       -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, -std=f2008 and -std=f2018. 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.

       -Wargument-mismatch
           Warn about type, rank, and other mismatches between formal
           parameters and actual arguments to functions and subroutines.
           These warnings are recommended and thus enabled by default.

       -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.  For free-form source code, the default
           is -Werror=line-truncation such that truncations are reported
           as error.

       -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. This option does not imply -Wconversion.

       -Wextra
           Enables some warning options for usages of language features
           which may be problematic. This currently includes
           -Wcompare-reals, -Wunused-parameter and -Wdo-subscript.

       -Wfrontend-loop-interchange
           Enable warning for loop interchanges performed by the
           -ffrontend-loop-interchange option.

       -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 explicit
           interface nor has been declared as "EXTERNAL".

       -Winteger-division
           Warn if a constant integer division truncates it result.  As
           an example, 3/5 evaluates to 0.

       -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:

           *   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.

           *   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.  -Wtabs will cause a warning to be issued if a tab
           is encountered. Note, -Wtabs is active for -pedantic,
           -std=f95, -std=f2003, -std=f2008, -std=f2018 and -Wall.

       -Wundefined-do-loop
           Warn if a DO loop with step either 1 or -1 yields an
           underflow or an overflow during iteration of an induction
           variable of the loop.  This option is implied by -Wall.

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

       -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.

       -Wuse-without-only
           Warn if a "USE" statement has no "ONLY" qualifier and thus
           implicitly imports all public entities of the used module.

       -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 implied by
           -Wextra if also -Wunused or -Wall is used.

       -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 impure functions are eliminated by the
           optimizations enabled by the -ffrontend-optimize option.
           This option is implied by -Wextra.

       -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.

       -Wtarget-lifetime
           Warn if the pointer in a pointer assignment might be longer
           than the its target. This option is implied by -Wall.

       -Wzerotrip
           Warn if a "DO" loop is known to execute zero times at compile
           time.  This option is implied by -Wall.

       -Wdo-subscript
           Warn if an array subscript inside a DO loop could lead to an
           out-of-bounds access even if the compiler cannot prove that
           the statement is actually executed, in cases like

                     real a(3)
                     do i=1,4
                       if (condition(i)) then
                         a(i) = 1.2
                       end if
                     end do

           This option is implied by -Wextra.

       -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.  This option is mostly
           useful for debugging the GNU Fortran compiler itself. The
           output generated by this option might change between
           releases. This option may also generate internal compiler
           errors for features which have only recently been added.

       -fdump-fortran-optimized
           Output the parse tree after front-end optimization.  Mostly
           useful for debugging the GNU Fortran compiler itself. The
           output generated by this option might change between
           releases.  This option may also generate internal compiler
           errors for features which have only recently been added.

       -fdump-parse-tree
           Output the internal parse tree after translating the source
           program into internal representation.  Mostly useful for
           debugging the GNU Fortran compiler itself. The output
           generated by this option might change between releases. This
           option may also generate internal compiler errors for
           features which have only recently been added. This option is
           deprecated; use "-fdump-fortran-original" instead.

       -fdump-fortran-global
           Output a list of the global identifiers after translating
           into middle-end representation. Mostly useful for debugging
           the GNU Fortran compiler itself. The output generated by this
           option might change between releases.  This option may also
           generate internal compiler errors for features which have
           only recently been added.

       -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 has
           provisions for dealing with these exceptions, enabling traps
           for these three exceptions is probably a good idea.

           If the option is used more than once in the command line, the
           lists will be joined: '"ffpe-trap="list1 "ffpe-trap="list2'
           is equivalent to "ffpe-trap="list1,list2.

           Note that once enabled an exception cannot be disabled (no
           negative form).

           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.

       -ffpe-summary=list
           Specify a list of floating-point exceptions, whose flag
           status is printed to "ERROR_UNIT" when invoking "STOP" and
           "ERROR STOP".  list can be either none, all or a comma-
           separated list of the following exceptions: invalid, zero,
           overflow, underflow, inexact and denormal. (See -ffpe-trap
           for a description of the exceptions.)

           If the option is used more than once in the command line,
           only the last one will be used.

           By default, a summary for all exceptions but inexact is
           shown.

       -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 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 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.

           Local variables or arrays having an explicit "SAVE" attribute
           are silently ignored unless the -pedantic option is added.

       -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 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.

       -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.
           Prefixing a check with no- disables it if it was activated by
           a previous specification.

           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
               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.

           Example: Assuming you have a file foo.f90, the command

                     gfortran -fcheck=all,no-array-temps foo.f90

           will compile the file with all checks enabled as specified
           above except warnings for generated array temporaries.

       -fbounds-check
           Deprecated alias for -fcheck=bounds.

       -ftail-call-workaround
       -ftail-call-workaround=n
           Some C interfaces to Fortran codes violate the gfortran ABI
           by omitting the hidden character length arguments as
           described in
             This can lead to crashes because pushing arguments for tail
           calls can overflow the stack.

           To provide a workaround for existing binary packages, this
           option disables tail call optimization for gfortran
           procedures with character arguments.  With
           -ftail-call-workaround=2 tail call optimization is disabled
           in all gfortran procedures with character arguments, with
           -ftail-call-workaround=1 or equivalent -ftail-call-workaround
           only in gfortran procedures with character arguments that
           call implicitly prototyped procedures.

           Using this option can lead to problems including crashes due
           to insufficient stack space.

           It is very strongly recommended to fix the code in question.
           The -fc-prototypes-external option can be used to generate
           prototypes which conform to gfortran's ABI, for inclusion in
           the source code.

           Support for this option will likely be withdrawn in a future
           release of gfortran.

           The negative form, -fno-tail-call-workaround or equivalent
           -ftail-call-workaround=0, can be used to disable this option.

           Default is currently -ftail-call-workaround, this will change
           in future releases.

       -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.

           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
           arrays of unknown size and array temporaries 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 unless
           -fmax-stack-var-size is specified.

       -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.

       -finline-matmul-limit=n
           When front-end optimiztion is active, some calls to the
           "MATMUL" intrinsic function will be inlined.  This may result
           in code size increase if the size of the matrix cannot be
           determined at compile time, as code for both cases is
           generated.  Setting "-finline-matmul-limit=0" will disable
           inlining in all cases.  Setting this option with a value of n
           will produce inline code for matrices with size up to n. 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.  The "-fblas-matmul-limit" can
           be used to change this value.

       -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-derived
       -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.

           With -finit-derived, components of derived type variables
           will be initialized according to these flags.  Components
           whose type is not covered by an explicit -finit-* flag will
           be treated as described above with -finit-local-zero.

           These options do not initialize

           *   objects with the POINTER attribute

           *   allocatable arrays

           *   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).

           The -finit-integer option will parse the value into an
           integer of type "INTEGER(kind=C_LONG)" on the host.  Said
           value is then assigned to the integer variables in the
           Fortran code, which might result in wraparound if the value
           is too large for the kind.

           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. 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 except -O0 and -Og.  Optimizations
           enabled by this option include:

           *<inlining calls to "MATMUL",>
           *<elimination of identical function calls within
           expressions,>
           *<removing unnecessary calls to "TRIM" in comparisons and
           assignments,>
           *<replacing TRIM(a) with "a(1:LEN_TRIM(a))" and>
           *<short-circuiting of logical operators (".AND." and
           ".OR.").>

           It can be deselected by specifying -fno-frontend-optimize.

       -ffrontend-loop-interchange
           Attempt to interchange loops in the Fortran front end where
           profitable.  Enabled by default by any -O option.  At the
           moment, this option only affects "FORALL" and "DO CONCURRENT"
           statements with several forall triplets.

ENVIRONMENT         top

       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         top

       For instructions on reporting bugs, see
       <https://gcc.gnu.org/bugs/ >.

SEE ALSO         top

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

AUTHOR         top

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

COPYRIGHT         top

       Copyright (c) 2004-2019 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.

COLOPHON         top

       This page is part of the gcc (GNU Compiler Collection) project.
       Information about the project can be found at 
       ⟨http://gcc.gnu.org/⟩.  If you have a bug report for this manual
       page, see ⟨http://gcc.gnu.org/bugs/⟩.  This page was obtained
       from the tarball gcc-9.3.0.tar.gz fetched from
       ⟨ftp://ftp.gwdg.de/pub/misc/gcc/releases/⟩ on 2020-12-18.  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to man-pages@man7.org

gcc-9.3.0                      2020-03-12                    GFORTRAN(1)