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NAME

       gfortran - GNU Fortran compiler

SYNOPSIS

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

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

DESCRIPTION

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

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

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

OPTIONS

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

       Fortran Language Options
           -fall-intrinsics -fbackslash -fcray-pointer -fd-lines-as-code -fd-lines-as-comments
           -fdefault-double-8 -fdefault-integer-8 -fdefault-real-8 -fdollar-ok
           -ffixed-line-length-n -ffixed-line-length-none -ffree-form -ffree-line-length-n
           -ffree-line-length-none -fimplicit-none -finteger-4-integer-8 -fmax-identifier-length
           -fmodule-private -fno-fixed-form -fno-range-check -fopenmp -freal-4-real-10
           -freal-4-real-16 -freal-4-real-8 -freal-8-real-10 -freal-8-real-16 -freal-8-real-4
           -std=std

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

       Error and Warning Options
           -Waliasing -Wall -Wampersand -Warray-bounds -Wc-binding-type -Wcharacter-truncation
           -Wconversion -Wfunction-elimination -Wimplicit-interface -Wimplicit-procedure
           -Wintrinsic-shadow -Wintrinsics-std -Wline-truncation -Wno-align-commons -Wno-tabs
           -Wreal-q-constant -Wsurprising -Wunderflow -Wunused-parameter -Wrealloc-lhs Wrealloc-
           lhs-all -Wtarget-lifetime -fmax-errors=n -fsyntax-only -pedantic -pedantic-errors

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

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

       Link Options
           -static-libgfortran

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

       Code Generation Options
           -faggressive-function-elimination -fblas-matmul-limit=n -fbounds-check
           -fcheck-array-temporaries -fcheck=<all|array-temps|bounds|do|mem|pointer|recursion>
           -fcoarray=<none|single|lib> -fexternal-blas -ff2c -ffrontend-optimize
           -finit-character=n -finit-integer=n -finit-local-zero -finit-logical=<true|false>
           -finit-real=<zero|inf|-inf|nan|snan> -fmax-array-constructor=n -fmax-stack-var-size=n
           -fno-align-commons -fno-automatic -fno-protect-parens -fno-underscoring
           -fno-whole-file -fsecond-underscore -fpack-derived -frealloc-lhs -frecursive
           -frepack-arrays -fshort-enums -fstack-arrays

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

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

       -fall-intrinsics
           This option causes all intrinsic procedures (including the GNU-specific extensions) to
           be accepted.  This can be useful with -std=f95 to force standard-compliance but get
           access to the full range of intrinsics available with gfortran.  As a consequence,
           -Wintrinsics-std will be ignored and no user-defined procedure with the same name as
           any intrinsic will be called except when it is explicitly declared "EXTERNAL".

       -fd-lines-as-code
       -fd-lines-as-comments
           Enable special treatment for lines beginning with "d" or "D" in fixed form sources.
           If the -fd-lines-as-code option is given they are treated as if the first column
           contained a blank.  If the -fd-lines-as-comments option is given, they are treated as
           comment lines.

       -fdefault-double-8
           Set the "DOUBLE PRECISION" type to an 8 byte wide type.  If -fdefault-real-8 is given,
           "DOUBLE PRECISION" would instead be promoted to 16 bytes if possible, and
           -fdefault-double-8 can be used to prevent this.  The kind of real constants like
           "1.d0" will not be changed by -fdefault-real-8 though, so also -fdefault-double-8 does
           not affect it.

       -fdefault-integer-8
           Set the default integer and logical types to an 8 byte wide type.  Do nothing if this
           is already the default.  This option also affects the kind of integer constants like
           42.

       -fdefault-real-8
           Set the default real type to an 8 byte wide type.  Do nothing if this is already the
           default.  This option also affects the kind of non-double real constants like 1.0, and
           does promote the default width of "DOUBLE PRECISION" to 16 bytes if possible, unless
           "-fdefault-double-8" is given, too.

       -fdollar-ok
           Allow $ as a valid non-first character in a symbol name. Symbols that start with $ are
           rejected since it is unclear which rules to apply to implicit typing as different
           vendors implement different rules.  Using $ in "IMPLICIT" statements is also rejected.

       -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.

       -finteger-4-integer-8
           Promote all "INTEGER(KIND=4)" entities to an "INTEGER(KIND=8)" entities.  If "KIND=8"
           is unavailable, then an error will be issued.  This option should be used with care
           and may not be suitable for your codes.  Areas of possible concern include calls to
           external procedures, alignment in "EQUIVALENCE" and/or "COMMON", generic interfaces,
           BOZ literal constant conversion, and I/O.  Inspection of the intermediate
           representation of the translated Fortran code, produced by -fdump-tree-original, is
           suggested.

       -fcray-pointer
           Enable the Cray pointer extension, which provides C-like pointer functionality.

       -fopenmp
           Enable the OpenMP extensions.  This includes OpenMP "!$omp" directives in free form
           and "c$omp", *$omp and "!$omp" directives in fixed form, "!$" conditional compilation
           sentinels in free form and "c$", "*$" and "!$" sentinels in fixed form, and when
           linking arranges for the OpenMP runtime library to be linked in.  The option -fopenmp
           implies -frecursive.

       -fno-range-check
           Disable range checking on results of simplification of constant expressions during
           compilation.  For example, GNU Fortran will give an error at compile time when
           simplifying "a = 1. / 0".  With this option, no error will be given and "a" will be
           assigned the value "+Infinity".  If an expression evaluates to a value outside of the
           relevant range of ["-HUGE()":"HUGE()"], then the expression will be replaced by "-Inf"
           or "+Inf" as appropriate.  Similarly, "DATA i/Z'FFFFFFFF'/" will result in an integer
           overflow on most systems, but with -fno-range-check the value will "wrap around" and
           "i" will be initialized to -1 instead.

       -freal-4-real-8
       -freal-4-real-10
       -freal-8-real-4
       -freal-8-real-10
       -freal-8-real-16
           Promote all "REAL(KIND=M)" entities to "REAL(KIND=N)" entities.  If "REAL(KIND=N)" is
           unavailable, then an error will be issued.  All other real kind types are unaffected
           by this option.  These options should be used with care and may not be suitable for
           your codes.  Areas of possible concern include calls to external procedures, alignment
           in "EQUIVALENCE" and/or "COMMON", generic interfaces, BOZ literal constant conversion,
           and I/O.  Inspection of the intermediate representation of the translated Fortran
           code, produced by -fdump-tree-original, is suggested.

       -std=std
           Specify the standard to which the program is expected to conform, which may be one of
           f95, f2003, f2008, gnu, or legacy.  The default value for std is gnu, which specifies
           a superset of the Fortran 95 standard that includes all of the extensions supported by
           GNU Fortran, although warnings will be given for obsolete extensions not recommended
           for use in new code.  The legacy value is equivalent but without the warnings for
           obsolete extensions, and may be useful for old non-standard programs.  The f95, f2003
           and f2008 values specify strict conformance to the Fortran 95, Fortran 2003 and
           Fortran 2008 standards, respectively; errors are given for all extensions beyond the
           relevant language standard, and warnings are given for the Fortran 77 features that
           are permitted but obsolescent in later standards. -std=f2008ts allows the Fortran 2008
           standard including the additions of the Technical Specification (TS) 29113 on Further
           Interoperability of Fortran with C.

   Enable and customize preprocessing
       Preprocessor related options. See section Preprocessing and conditional compilation for
       more detailed information on preprocessing in gfortran.

       -cpp
       -nocpp
           Enable preprocessing. The preprocessor is automatically invoked if the file extension
           is .fpp, .FPP,  .F, .FOR, .FTN, .F90, .F95, .F03 or .F08. Use this option to manually
           enable preprocessing of any kind of Fortran file.

           To disable preprocessing of files with any of the above listed extensions, use the
           negative form: -nocpp.

           The preprocessor is run in traditional mode. Any restrictions of the file-format,
           especially the limits on line length, apply for preprocessed output as well, so it
           might be advisable to use the -ffree-line-length-none or -ffixed-line-length-none
           options.

       -dM Instead of the normal output, generate a list of '#define' directives for all the
           macros defined during the execution of the preprocessor, including predefined macros.
           This gives you a way of finding out what is 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.

       -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, -Wconversion, -Wsurprising, -Wc-binding-type, -Wintrinsics-std,
           -Wno-tabs, -Wintrinsic-shadow, -Wline-truncation, -Wtarget-lifetime, -Wreal-q-constant
           and -Wunused.

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

           The following example will trigger the warning.

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

                     call bar(a,a)

       -Wampersand
           Warn about missing ampersand in continued character constants. The warning is given
           with -Wampersand, -pedantic, -std=f95, -std=f2003 and -std=f2008. Note: With no
           ampersand given in a continued character constant, GNU Fortran assumes continuation at
           the first non-comment, non-whitespace character after the ampersand that initiated the
           continuation.

       -Warray-temporaries
           Warn about array temporaries generated by the compiler.  The information generated by
           this warning is sometimes useful in optimization, in order to avoid such temporaries.

       -Wc-binding-type
           Warn if the a variable might not be C interoperable.  In particular, warn if the
           variable has been declared using an intrinsic type with default kind instead of using
           a kind parameter defined for C interoperability in the intrinsic "ISO_C_Binding"
           module.  This option is implied by -Wall.

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

       -Wline-truncation
           Warn when a source code line will be truncated.  This option is implied by -Wall.

       -Wconversion
           Warn about implicit conversions that are likely to change the value of the expression
           after conversion. Implied by -Wall.

       -Wconversion-extra
           Warn about implicit conversions between different types and kinds.

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

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

       -Wimplicit-procedure
           Warn if a procedure is called that has neither an explicit interface nor has been
           declared as "EXTERNAL".

       -Wintrinsics-std
           Warn if gfortran finds a procedure named like an intrinsic not available in the
           currently selected standard (with -std) and treats it as "EXTERNAL" procedure because
           of this.  -fall-intrinsics can be used to never trigger this behavior and always link
           to the intrinsic regardless of the selected standard.

       -Wreal-q-constant
           Produce a warning if a real-literal-constant contains a "q" exponent-letter.

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

           This currently produces a warning under the following circumstances:

           ·   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.  -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.  This option is implied by -Wall.

       -Wunused-dummy-argument
           Warn about unused dummy arguments. This option is implied by -Wall.

       -Wunused-parameter
           Contrary to gcc's meaning of -Wunused-parameter, gfortran's implementation of this
           option does not warn about unused dummy arguments (see -Wunused-dummy-argument), but
           about unused "PARAMETER" values. -Wunused-parameter is not included in -Wall but is
           implied by -Wall -Wextra.

       -Walign-commons
           By default, gfortran warns about any occasion of variables being padded for proper
           alignment inside a "COMMON" block. This warning can be turned off via
           -Wno-align-commons. See also -falign-commons.

       -Wfunction-elimination
           Warn if any calls to functions are eliminated by the optimizations enabled by the
           -ffrontend-optimize option.

       -Wrealloc-lhs
           Warn when the compiler might insert code to for allocation or reallocation of an
           allocatable array variable of intrinsic type in intrinsic assignments.  In hot loops,
           the Fortran 2003 reallocation feature may reduce the performance.  If the array is
           already allocated with the correct shape, consider using a whole-array array-spec
           (e.g. "(:,:,:)") for the variable on the left-hand side to prevent the reallocation
           check. Note that in some cases the warning is shown, even if the compiler will
           optimize reallocation checks away.  For instance, when the right-hand side contains
           the same variable multiplied by a scalar.  See also -frealloc-lhs.

       -Wrealloc-lhs-all
           Warn when the compiler inserts code to for allocation or reallocation of an
           allocatable variable; this includes scalars and derived types.

       -Wcompare-reals
           Warn when comparing real or complex types for equality or inequality.  This option is
           implied by -Wextra.

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

       -Werror
           Turns all warnings into errors.

       Some of these have no effect when compiling programs written in Fortran.

   Options for debugging your program or GNU Fortran
       GNU Fortran has various special options that are used for debugging either your program or
       the GNU Fortran compiler.

       -fdump-fortran-original
           Output the internal parse tree after translating the source program into internal
           representation.  Only really useful for debugging the GNU Fortran compiler itself.

       -fdump-fortran-optimized
           Output the parse tree after front-end optimization.  Only really useful for debugging
           the GNU Fortran compiler itself.

       -fdump-parse-tree
           Output the internal parse tree after translating the source program into internal
           representation.  Only really useful for debugging the GNU Fortran compiler itself.
           This option is deprecated; use "-fdump-fortran-original" instead.

       -ffpe-trap=list
           Specify a list of floating point exception traps to enable.  On most systems, if a
           floating point exception occurs and the trap for that exception is enabled, a SIGFPE
           signal will be sent and the program being aborted, producing a core file useful for
           debugging.  list is a (possibly empty) comma-separated list of the following
           exceptions: invalid (invalid floating point operation, such as "SQRT(-1.0)"), zero
           (division by zero), overflow (overflow in a floating point operation), underflow
           (underflow in a floating point operation), inexact (loss of precision during
           operation), and denormal (operation performed on a denormal value).  The first five
           exceptions correspond to the five IEEE 754 exceptions, whereas the last one (denormal)
           is not part of the IEEE 754 standard but is available on some common architectures
           such as x86.

           The first three exceptions (invalid, zero, and overflow) often indicate serious
           errors, and unless the program has provisions for dealing with these exceptions,
           enabling traps for these three exceptions is probably a good idea.

           Many, if not most, floating point operations incur loss of precision due to rounding,
           and hence the "ffpe-trap=inexact" is likely to be uninteresting in practice.

           By default no exception traps are enabled.

       -fno-backtrace
           When a serious runtime error is encountered or a deadly signal is emitted
           (segmentation fault, illegal instruction, bus error, floating-point exception, and the
           other POSIX signals that have the action core), the Fortran runtime library tries to
           output a backtrace of the error. "-fno-backtrace" disables the backtrace generation.
           This option only has influence for compilation of the Fortran main program.

   Options for directory search
       These options affect how GNU Fortran searches for files specified by the "INCLUDE"
       directive and where it searches for previously compiled modules.

       It also affects the search paths used by cpp when used to preprocess Fortran source.

       -Idir
           These affect interpretation of the "INCLUDE" directive (as well as of the "#include"
           directive of the cpp preprocessor).

           Also note that the general behavior of -I and "INCLUDE" is pretty much the same as of
           -I with "#include" in the cpp preprocessor, with regard to looking for header.gcc
           files and other such things.

           This path is also used to search for .mod files when previously compiled modules are
           required by a "USE" statement.

       -Jdir
           This option specifies where to put .mod files for compiled modules.  It is also added
           to the list of directories to searched by an "USE" statement.

           The default is the current directory.

       -fintrinsic-modules-path dir
           This option specifies the location of pre-compiled 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.

       -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.

       -fno-whole-file
           This flag causes the compiler to resolve and translate each procedure in a file
           separately.

           By default, the whole file is parsed and placed in a single front-end tree.  During
           resolution, in addition to all the usual checks and fixups, references to external
           procedures that are in the same file effect resolution of that procedure, if not
           already done, and a check of the interfaces.  The dependences are resolved by changing
           the order in which the file is translated into the backend tree.  Thus, a procedure
           that is referenced is translated before the reference and the duplication of backend
           tree declarations eliminated.

           The -fno-whole-file option is deprecated and may lead to wrong code.

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

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

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

       -fcoarray=<keyword>
           none
               Disable coarray support; using coarray declarations and image-control statements
               will produce a compile-time error. (Default)

           single
               Single-image mode, i.e. "num_images()" is always one.

           lib Library-based coarray parallelization; a suitable GNU Fortran coarray library
               needs to be linked.

       -fcheck=<keyword>
           Enable the generation of run-time checks; the argument shall be a comma-delimited list
           of the following keywords.

           all Enable all run-time test of -fcheck.

           array-temps
               Warns at run time when for passing an actual argument a temporary array had to be
               generated. The information generated by this warning is sometimes useful in
               optimization, in order to avoid such temporaries.

               Note: The warning is only printed once per location.

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

               Some checks require that -fcheck=bounds is set for the compilation of the main
               program.

               Note: In the future this may also include other forms of checking, e.g., checking
               substring references.

           do  Enable generation of run-time checks for invalid modification of loop iteration
               variables.

           mem Enable generation of run-time checks for memory allocation.  Note: This option
               does not affect explicit allocations using the "ALLOCATE" statement, which will be
               always checked.

           pointer
               Enable generation of run-time checks for pointers and allocatables.

           recursion
               Enable generation of run-time checks for recursively called subroutines and
               functions which are not marked as recursive. See also -frecursive.  Note: This
               check does not work for OpenMP programs and is disabled if used together with
               -frecursive and -fopenmp.

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

       -fcheck-array-temporaries
           Deprecated alias for -fcheck=array-temps.

       -fmax-array-constructor=n
           This option can be used to increase the upper limit permitted in array constructors.
           The code below requires this option to expand the array at compile time.

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

           Caution:  This option can lead to long compile times and excessively large object
           files.

           The default value for n is 65535.

       -fmax-stack-var-size=n
           This option specifies the size in bytes of the largest array that will be put on the
           stack; if the size is exceeded static memory is used (except in procedures marked as
           RECURSIVE). Use the option -frecursive to allow for recursive procedures which do not
           have a RECURSIVE attribute or for parallel programs. Use -fno-automatic to never use
           the stack.

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

           The default value for n is 32768.

       -fstack-arrays
           Adding this option will make the Fortran compiler put all local arrays, even those of
           unknown size onto stack memory.  If your program uses very large local arrays it is
           possible that you will have to extend your runtime limits for stack memory on some
           operating systems. This flag is enabled by default at optimization level -Ofast.

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

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

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

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

       -fexternal-blas
           This option will make gfortran generate calls to BLAS functions for some matrix
           operations like "MATMUL", instead of using our own algorithms, if the size of the
           matrices involved is larger than a given limit (see -fblas-matmul-limit).  This may be
           profitable if an optimized vendor BLAS library is available.  The BLAS library will
           have to be specified at link time.

       -fblas-matmul-limit=n
           Only significant when -fexternal-blas is in effect.  Matrix multiplication of matrices
           with size larger than (or equal to) n will be performed by calls to BLAS functions,
           while others will be handled by gfortran internal algorithms. If the matrices involved
           are not square, the size comparison is performed using the geometric mean of the
           dimensions of the argument and result matrices.

           The default value for n is 30.

       -frecursive
           Allow indirect recursion by forcing all local arrays to be allocated on the stack.
           This flag cannot be used together with -fmax-stack-var-size= or -fno-automatic.

       -finit-local-zero
       -finit-integer=n
       -finit-real=<zero|inf|-inf|nan|snan>
       -finit-logical=<true|false>
       -finit-character=n
           The -finit-local-zero option instructs the compiler to initialize local "INTEGER",
           "REAL", and "COMPLEX" variables to zero, "LOGICAL" variables to false, and "CHARACTER"
           variables to a string of null bytes.  Finer-grained initialization options are
           provided by the -finit-integer=n, -finit-real=<zero|inf|-inf|nan|snan> (which also
           initializes the real and imaginary parts of local "COMPLEX" variables),
           -finit-logical=<true|false>, and -finit-character=n (where n is an ASCII character
           value) options.  These options do not initialize

           ·   allocatable arrays

           ·   components of derived type variables

           ·   variables that appear in an "EQUIVALENCE" statement.

           (These limitations may be removed in future releases).

           Note that the -finit-real=nan option initializes "REAL" and "COMPLEX" variables with a
           quiet NaN. For a signalling NaN use -finit-real=snan; note, however, that compile-time
           optimizations may convert them into quiet NaN and that trapping needs to be enabled
           (e.g. via -ffpe-trap).

           Finally, note that enabling any of the -finit-* options will silence warnings that
           would have been emitted by -Wuninitialized for the affected local variables.

       -falign-commons
           By default, gfortran enforces proper alignment of all variables in a "COMMON" block by
           padding them as needed. On certain platforms this is mandatory, on others it increases
           performance. If a "COMMON" block is not declared with consistent data types
           everywhere, this padding can cause trouble, and -fno-align-commons can be used to
           disable automatic alignment. The same form of this option should be used for all files
           that share a "COMMON" block.  To avoid potential alignment issues in "COMMON" blocks,
           it is recommended to order objects from largest to smallest.

       -fno-protect-parens
           By default the parentheses in expression are honored for all optimization levels such
           that the compiler does not do any re-association. Using -fno-protect-parens allows the
           compiler to reorder "REAL" and "COMPLEX" expressions to produce faster code. Note that
           for the re-association optimization -fno-signed-zeros and -fno-trapping-math need to
           be in effect. The parentheses protection is enabled by default, unless -Ofast is
           given.

       -frealloc-lhs
           An allocatable left-hand side of an intrinsic assignment is automatically
           (re)allocated if it is either unallocated or has a different shape. The option is
           enabled by default except when -std=f95 is given. See also -Wrealloc-lhs.

       -faggressive-function-elimination
           Functions with identical argument lists are eliminated within statements, regardless
           of whether these functions are marked "PURE" or not. For example, in

                     a = f(b,c) + f(b,c)

           there will only be a single call to "f".  This option only works if
           -ffrontend-optimize is in effect.

       -ffrontend-optimize
           This option performs front-end optimization, based on manipulating parts the Fortran
           parse tree.  Enabled by default by any -O option.  Optimizations enabled by this
           option include elimination of identical function calls within expressions, removing
           unnecessary calls to "TRIM" in comparisons and assignments and replacing TRIM(a) with
           "a(1:LEN_TRIM(a))".  It can be deselected by specifying -fno-frontend-optimize.

ENVIRONMENT

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

BUGS

       For instructions on reporting bugs, see <file:///usr/share/doc/gcc-4.8/README.Bugs>.

SEE ALSO

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

AUTHOR

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

COPYRIGHT

       Copyright (c) 2004-2013 Free Software Foundation, Inc.

       Permission is granted to copy, distribute and/or modify this document under the terms of
       the GNU Free Documentation License, Version 1.3 or any later version published by the Free
       Software Foundation; with the Invariant Sections being "Funding Free Software", the Front-
       Cover Texts being (a) (see below), and with the Back-Cover Texts being (b) (see below).  A
       copy of the license is included in the gfdl(7) man page.

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

            A GNU Manual

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

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