@c Copyright (C) 2004,2005 @c Free Software Foundation, Inc. @c This is part of the GFORTRAN manual. @c For copying conditions, see the file gfortran.texi. @ignore @c man begin COPYRIGHT Copyright @copyright{} 2004 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with the Invariant Sections being ``GNU General Public License'' and ``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. @c man end @c Set file name and title for the man page. @setfilename gfortran @settitle GNU Fortran 95 compiler. @c man begin SYNOPSIS gfortran [@option{-c}|@option{-S}|@option{-E}] [@option{-g}] [@option{-pg}] [@option{-O}@var{level}] [@option{-W}@var{warn}@dots{}] [@option{-pedantic}] [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}] [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}] [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}] [@option{-o} @var{outfile}] @var{infile}@dots{} Only the most useful options are listed here; see below for the remainder. @c man end @c man begin SEEALSO 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 @file{gcc}, @file{cpp}, @file{gfortran}, @file{as}, @file{ld}, @file{binutils} and @file{gdb}. @c man end @c man begin BUGS For instructions on reporting bugs, see @w{@uref{http://gcc.gnu.org/bugs.html}}. @c man end @c man begin AUTHOR See the Info entry for @command{gfortran} for contributors to GCC and GFORTRAN@. @c man end @end ignore @node Invoking GFORTRAN @chapter GNU Fortran 95 Command Options @cindex GNU Fortran 95 command options @cindex command options @cindex options, GNU Fortran 95 command @c man begin DESCRIPTION The @command{gfortran} command supports all the options supported by the @command{gcc} command. Only options specific to gfortran are documented here. @emph{Gfortran is not yet a fully conformant Fortran 95 compiler}. It can generate code for most constructs and expressions, but work remains to be done. In particular, there are known deficiencies with ENTRY, NAMELIST, and sophisticated use of MODULES, POINTERS and DERIVED TYPES. For those whose Fortran codes conform to either the Fortran 77 standard or the GNU Fortran 77 language, we recommend to use @command{g77} from GCC 3.4. We recommend that distributors continue to provide packages of g77-3.4 until we announce that @command{gfortran} fully replaces @command{g77}. The gfortran developers welcome any feedback on user experience with @command{gfortran} at @email{fortran@@gcc.gnu.org}. @xref{Invoking GCC,,GCC Command Options,gcc,Using the GNU Compiler Collection (GCC)}, for information on the non-Fortran-specific aspects of the @command{gcc} command (and, therefore, the @command{gfortran} command). @cindex options, negative forms @cindex negative forms of options All @command{gcc} and @command{gfortran} options are accepted both by @command{gfortran} and by @command{gcc} (as well as any other drivers built at the same time, such as @command{g++}), since adding @command{gfortran} to the @command{gcc} distribution enables acceptance of @command{gfortran} options by all of the relevant drivers. In some cases, options have positive and negative forms; the negative form of @option{-ffoo} would be @option{-fno-foo}. This manual documents only one of these two forms, whichever one is not the default. @c man end @menu * Option Summary:: Brief list of all @command{gfortran} options, without explanations. * Fortran Dialect Options:: Controlling the variant of Fortran language compiled. * Warning Options:: How picky should the compiler be? * Debugging Options:: Symbol tables, measurements, and debugging dumps. * Directory Options:: Where to find module files * Code Gen Options:: Specifying conventions for function calls, data layout and register usage. * Environment Variables:: Env vars that affect GNU Fortran. @end menu @node Option Summary @section Option Summary @c man begin OPTIONS Here is a summary of all the options specific to GNU Fortran, grouped by type. Explanations are in the following sections. @table @emph @item Fortran Language Options @xref{Fortran Dialect Options,,Options Controlling Fortran Dialect}. @gccoptlist{ -ffree-form -fno-fixed-form @gol -fdollar-ok -fimplicit-none -fmax-identifier-length @gol -std=@var{std} -ffixed-line-length-@var{n} -ffixed-line-length-none @gol -fdefault-double-8 -fdefault-integer-8 -fdefault-real-8 } @item Warning Options @xref{Warning Options,,Options to Request or Suppress Warnings}. @gccoptlist{ -fsyntax-only -pedantic -pedantic-errors @gol -w -Wall -Waliasing -Wconversion @gol -Wimplicit-interface -Wnonstd-intrinsics -Wsurprising -Wunderflow @gol -Wunused-labels -Wline-truncation @gol -Werror -W} @item Debugging Options @xref{Debugging Options,,Options for Debugging Your Program or GCC}. @gccoptlist{ -fdump-parse-tree} @item Directory Options @xref{Directory Options,,Options for Directory Search}. @gccoptlist{ -I@var{dir} -M@var{dir}} @item Code Generation Options @xref{Code Gen Options,,Options for Code Generation Conventions}. @gccoptlist{ -ff2c -fno-underscoring -fsecond-underscore @gol -fbounds-check -fmax-stack-var-size=@var{n} @gol -fpackderived -frepack-arrays} @end table @menu * Fortran Dialect Options:: Controlling the variant of Fortran language compiled. * Warning Options:: How picky should the compiler be? * Debugging Options:: Symbol tables, measurements, and debugging dumps. * Directory Options:: Where to find module files * Code Gen Options:: Specifying conventions for function calls, data layout and register usage. @end menu @node Fortran Dialect Options @section Options Controlling Fortran Dialect @cindex dialect options @cindex language, dialect options @cindex options, dialect The following options control the dialect of Fortran that the compiler accepts: @table @gcctabopt @cindex -ffree-form option @cindex options, -ffree-form @cindex -fno-fixed-form option @cindex options, -fno-fixed-form @cindex source file format @cindex free form @cindex fixed form @cindex Source Form @cindex Fortran 90, features @item -ffree-form @item -ffixed-form Specify the layout used by the the source file. The free form layout was introduced in Fortran 90. Fixed form was traditionally used in older Fortran programs. @cindex option, -fdefault-double-8 @cindex -fdefault-double-8, option @item -fdefault-double-8 Set the "DOUBLE PRECISION" type to an 8 byte wide. @cindex option, -fdefault-integer-8 @cindex -fdefault-integer-8, option @item -fdefault-integer-8 Set the default integer and logical types to an 8 byte wide type. Do nothing if this is already the default. @cindex option, -fdefault-real-8 @cindex -fdefault-real-8, option @item -fdefault-real-8 Set the default real type to an 8 byte wide type. Do nothing if this is already the default. @cindex -fdollar-ok option @cindex options, -fdollar-ok @item -fdollar-ok @cindex dollar sign @cindex symbol names @cindex character set Allow @samp{$} as a valid character in a symbol name. @cindex -fno-backslash option @cindex options, -fno-backslash @item -fno-backslash @cindex backslash @cindex escape characters @item Compile switch to change the interpretation of a backslash from ``C''-style escape characters to a single backslash character. @cindex -ffixed-line-length-@var{n} option @cindex options, -ffixed-line-length-@var{n} @item -ffixed-line-length-@var{n} @cindex source file format @cindex lines, length @cindex length of source lines @cindex fixed form @cindex limits, lengths of source lines 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. @cindex card image @cindex extended-source option Popular values for @var{n} include 72 (the standard and the default), 80 (card image), and 132 (corresponds to ``extended-source'' options in some popular compilers). @var{n} may be @samp{none}, meaning that the entire line is meaningful and that continued character constants never have implicit spaces appended to them to fill out the line. @option{-ffixed-line-length-0} means the same thing as @option{-ffixed-line-length-none}. @cindex -fmax-identifier-length=@var{n} option @cindex option -fmax-identifier-length=@var{n} @item -fmax-identifier-length=@var{n} Specify the maximum allowed identifier length. Typical values are 31 (Fortran 95) and 63 (Fortran 200x). @cindex -fimplicit-none option @cindex options, -fimplicit-none @item -fimplicit-none Specify that no implicit typing is allowed, unless overridden by explicit @samp{IMPLICIT} statements. This is the equivalent of adding @samp{implicit none} to the start of every procedure. @cindex -std=@var{std} option @cindex option, -std=@var{std} @item -std=@var{std} Conform to the specified standard. Allowed values for @var{std} are @samp{gnu} and @samp{f95}. @end table @node Warning Options @section Options to Request or Suppress Warnings @cindex options, warnings @cindex warnings, suppressing @cindex messages, warning @cindex suppressing warnings Warnings are diagnostic messages that report constructions which are not inherently erroneous but which are risky or suggest there might have been an error. You can request many specific warnings with options beginning @option{-W}, for example @option{-Wimplicit} to request warnings on implicit declarations. Each of these specific warning options also has a negative form beginning @option{-Wno-} to turn off warnings; for example, @option{-Wno-implicit}. This manual lists only one of the two forms, whichever is not the default. These options control the amount and kinds of warnings produced by GNU Fortran: @table @gcctabopt @cindex syntax checking @cindex -fsyntax-only option @cindex options, -fsyntax-only @item -fsyntax-only Check the code for syntax errors, but don't do anything beyond that. @cindex -pedantic option @cindex options, -pedantic @item -pedantic Issue warnings for uses of extensions to FORTRAN 95. @option{-pedantic} also applies to C-language constructs where they occur in GNU Fortran source files, such as use of @samp{\e} in a character constant within a directive like @samp{#include}. 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 @option{-pedantic} to check programs for conformance. They soon find that it does not do quite what they want---it finds some nonstandard practices, but not all. However, improvements to @command{gfortran} in this area are welcome. This should be used in conjunction with -std=@var{std}. @cindex -pedantic-errors option @cindex options, -pedantic-errors @item -pedantic-errors Like @option{-pedantic}, except that errors are produced rather than warnings. @cindex -w option @cindex options, -w @item -w Inhibit all warning messages. @cindex -Wall option @cindex options, -Wall @item -Wall @cindex all warnings @cindex warnings, all Enables commonly used warning options that which pertain to usage that we recommend avoiding and that we believe is easy to avoid. This currently includes @option{-Wunused-labels}, @option{-Waliasing}, @option{-Wsurprising}, @option{-Wnonstd-intrinsic} and @option{-Wline-truncation}. @cindex -Waliasing option @cindex options, -Waliasing @item -Waliasing @cindex aliasing Warn about possible aliasing of dummy arguments. The following example will trigger the warning as it would be illegal to @code{bar} to modify either parameter. @smallexample INTEGER A CALL BAR(A,A) @end smallexample @cindex -Wconversion option @cindex options, -Wconversion @item -Wconversion @cindex conversion Warn about implicit conversions between different types. @cindex -Wimplicit-interface option @cindex options, -Wimplicit-interface @item -Wimplicit-interface Warn about when procedure are 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. @cindex -Wnonstd-intrinsic option @cindex options, -Wnonstd-intrinsic @item -Wnonstd-intrinsic Warn if the user tries to use an intrinsic that does not belong to the standard the user has chosen via the -std option. @cindex -Wsurprising @cindex options, -Wsurprising @item -Wsurprising @cindex Suspicious 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: @itemize @bullet @item An INTEGER SELECT construct has a CASE that can never be matched as its lower value is greater than its upper value. @item A LOGICAL SELECT construct has three CASE statements. @end itemize @cindex -Wunderflow @cindex options, -Wunderflow @item -Wunderflow @cindex UNDERFLOW Produce a warning when numerical constant expressions are encountered, which yield an UNDERFLOW during compilation. @cindex -Wunused-labels option @cindex options, -Wunused-labels @item -Wunused-labels @cindex unused labels @cindex labels, unused Warn whenever a label is defined but never referenced. @cindex -Werror @cindex options, -Werror @item -Werror Turns all warnings into errors. @cindex -W option @cindex options, -W @item -W @cindex extra warnings @cindex warnings, extra Turns on ``extra warnings'' and, if optimization is specified via @option{-O}, the @option{-Wuninitialized} option. (This might change in future versions of @command{gfortran} @end table @xref{Warning Options,,Options to Request or Suppress Warnings, gcc,Using the GNU Compiler Collection (GCC)}, for information on more options offered by the GBE shared by @command{gfortran}, @command{gcc} and other GNU compilers. Some of these have no effect when compiling programs written in Fortran. @node Debugging Options @section Options for Debugging Your Program or GNU Fortran @cindex options, debugging @cindex debugging information options GNU Fortran has various special options that are used for debugging either your program or @command{gfortran} @table @gcctabopt @cindex -fdump-parse-tree option @cindex option, -fdump-parse-tree @item -fdump-parse-tree Output the internal parse tree before starting code generation. Only really useful for debugging gfortran itself. @end table @xref{Debugging Options,,Options for Debugging Your Program or GCC, gcc,Using the GNU Compiler Collection (GCC)}, for more information on debugging options. @node Directory Options @section Options for Directory Search @cindex directory, options @cindex options, directory search @cindex search path @cindex INCLUDE directive @cindex directive, INCLUDE There options affect how affect how @command{gfortran} searches for files specified via the @code{INCLUDE} directive, and where it searches for previously compiled modules. It also affects the search paths used by @command{cpp} when used to preprocess Fortran source. @table @gcctabopt @cindex -Idir option @cindex options, -Idir @item -I@var{dir} @cindex directory, search paths for inclusion @cindex inclusion, directory search paths for @cindex search paths, for included files @cindex paths, search @cindex module search path These affect interpretation of the @code{INCLUDE} directive (as well as of the @code{#include} directive of the @command{cpp} preprocessor). Also note that the general behavior of @option{-I} and @code{INCLUDE} is pretty much the same as of @option{-I} with @code{#include} in the @command{cpp} preprocessor, with regard to looking for @file{header.gcc} files and other such things. This path is also used to search for @samp{.mod} files when previously compiled modules are required by a @code{USE} statement. @xref{Directory Options,,Options for Directory Search, gcc,Using the GNU Compiler Collection (GCC)}, for information on the @option{-I} option. @cindex -Mdir option @cindex option, -Mdir @item -M@var{dir} @item -J@var{dir} This option specifies where to put @samp{.mod} files for compiled modules. It is also added to the list of directories to searched by an @code{USE} statement. The default is the current directory. @option{-J} is an alias for @option{-M} to avoid conflicts with existing GCC options. @end table @node Code Gen Options @section Options for Code Generation Conventions @cindex code generation, conventions @cindex options, code generation @cindex run-time, options 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 @option{-ffoo} would be @option{-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 @option{no-} or adding it. @table @gcctabopt @cindex @option{-ff2c} option @cindex options, @option{-ff2c} @item -ff2c @cindex calling convention @cindex @command{f2c} calling convention @cindex @command{g77} calling convention @cindex libf2c calling convention Generate code designed to be compatible with code generated by @command{g77} and @command{f2c}. The calling conventions used by @command{g77} (originally implemented in @command{f2c}) require functions that return type default @code{REAL} to actually return the C type @code{double}, and functions that return type @code{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 @code{REAL} functions return the C type @code{float}, and @code{COMPLEX} functions return the GNU C type @code{complex}. Additionally, this option implies the @option{-fsecond-underscore} option, unless @option{-fno-second-underscore} is explicitly requested. This does not affect the generation of code that interfaces with the @command{libgfortran} library. @emph{Caution:} It is not a good idea to mix Fortran code compiled with @code{-ff2c} with code compiled with the default @code{-fno-f2c} calling conventions as, calling @code{COMPLEX} or default @code{REAL} functions between program parts which were compiled with different calling conventions will break at execution time. @emph{Caution:} This will break code which passes intrinsic functions of type default @code{REAL} or @code{COMPLEX} as actual arguments, as the library implementations use the @command{-fno-f2c} calling conventions. @cindex @option{-fno-underscoring option} @cindex options, @option{-fno-underscoring} @item -fno-underscoring @cindex underscore @cindex symbol names, underscores @cindex transforming symbol names @cindex symbol names, transforming Do not transform names of entities specified in the Fortran source file by appending underscores to them. With @option{-funderscoring} in effect, @command{gfortran} appends one underscore to external names with no underscores. This is done to ensure compatibility with code produced by many UNIX Fortran compilers. @emph{Caution}: The default behavior of @command{gfortran} is incompatible with @command{f2c} and @command{g77}, please use the @option{-ff2c} option if you want object files compiled with @option{gfortran} to be compatible with object code created with these tools. Use of @option{-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 @option{-funderscoring}, and assuming other defaults like @option{-fcase-lower} and that @samp{j()} and @samp{max_count()} are external functions while @samp{my_var} and @samp{lvar} are local variables, a statement like @smallexample I = J() + MAX_COUNT (MY_VAR, LVAR) @end smallexample @noindent is implemented as something akin to: @smallexample i = j_() + max_count__(&my_var__, &lvar); @end smallexample With @option{-fno-underscoring}, the same statement is implemented as: @smallexample i = j() + max_count(&my_var, &lvar); @end smallexample Use of @option{-fno-underscoring} allows direct specification of user-defined names while debugging and when interfacing @command{gfortran} code with other languages. Note that just because the names match does @emph{not} mean that the interface implemented by @command{gfortran} for an external name matches the interface implemented by some other language for that same name. That is, getting code produced by @command{gfortran} 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 @option{-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 @command{gfortran} 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. @cindex @option{-fsecond-underscore option} @cindex options, @option{-fsecond-underscore} @item -fsecond-underscore @cindex underscore @cindex symbol names, underscores @cindex transforming symbol names @cindex symbol names, transforming @cindex @command{f2c} calling convention @cindex @command{g77} calling convention @cindex libf2c calling convention By default, @command{gfortran} appends an underscore to external names. If this option is used @command{gfortran} appends two underscores to names with underscores and one underscore to external names with no underscores. (@command{gfortran} also appends two underscores to internal names with underscores to avoid naming collisions with external names. This option has no effect if @option{-fno-underscoring} is in effect. It is implied by the @option{-ff2c} option. Otherwise, with this option, an external name such as @samp{MAX_COUNT} is implemented as a reference to the link-time external symbol @samp{max_count__}, instead of @samp{max_count_}. This is required for compatibility with @command{g77} and @command{f2c}, and is implied by use of the @option{-ff2c} option. @cindex -fbounds-check option @cindex -ffortran-bounds-check option @item -fbounds-check @cindex bounds checking @cindex range checking @cindex array bounds checking @cindex subscript checking @cindex checking subscripts 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. In the future this may also include other forms of checking, eg. checking substring references. @cindex -fmax-stack-var-size option @item -fmax-stack-var-size=@var{n} This option specifies the size in bytes of the largest array that will be put on the stack. This option currently only affects local arrays declared with constant bounds, and may not apply to all character variables. Future versions of @command{gfortran} may improve this behavior. The default value for @var{n} is 32768. @cindex -fpackderived @item -fpackderived @cindex Structure packing This option tells gfortran to pack derived type members as closely as possible. Code compiled with this option is likely to be incompatible with code compiled without this option, and may execute slower. @cindex -frepack-arrays option @item -frepack-arrays @cindex Repacking arrays In some circumstances @command{gfortran} may pass assumed shape array sections via a descriptor describing a discontiguous area of memory. This option adds code to the function prologue to repack the data into a contiguous block at runtime. This should result in faster accesses to the array. However it can introduce significant overhead to the function call, especially when the passed data is discontiguous. @end table @xref{Code Gen Options,,Options for Code Generation Conventions, gcc,Using the GNU Compiler Collection (GCC)}, for information on more options offered by the GBE shared by @command{gfortran} @command{gcc} and other GNU compilers. @c man end @node Environment Variables @section Environment Variables Affecting GNU Fortran @cindex environment variables @c man begin ENVIRONMENT GNU Fortran 95 currently does not make use of any environment variables to control its operation above and beyond those that affect the operation of @command{gcc}. @xref{Environment Variables,,Environment Variables Affecting GCC, gcc,Using the GNU Compiler Collection (GCC)}, for information on environment variables. @c man end