.\" Automatically generated by Pod::Man 2.16 (Pod::Simple 3.05) .\" .\" Standard preamble: .\" ======================================================================== .de Sh \" Subsection heading .br .if t .Sp .ne 5 .PP \fB\\$1\fR .PP .. .de Sp \" Vertical space (when we can't use .PP) .if t .sp .5v .if n .sp .. .de Vb \" Begin verbatim text .ft CW .nf .ne \\$1 .. .de Ve \" End verbatim text .ft R .fi .. .\" Set up some character translations and predefined strings. \*(-- will .\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left .\" double quote, and \*(R" will give a right double quote. \*(C+ will .\" give a nicer C++. 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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" gfortran \- GNU Fortran compiler .SH "SYNOPSIS" .IX Header "SYNOPSIS" gfortran [\fB\-c\fR|\fB\-S\fR|\fB\-E\fR] [\fB\-g\fR] [\fB\-pg\fR] [\fB\-O\fR\fIlevel\fR] [\fB\-W\fR\fIwarn\fR...] [\fB\-pedantic\fR] [\fB\-I\fR\fIdir\fR...] [\fB\-L\fR\fIdir\fR...] [\fB\-D\fR\fImacro\fR[=\fIdefn\fR]...] [\fB\-U\fR\fImacro\fR] [\fB\-f\fR\fIoption\fR...] [\fB\-m\fR\fImachine-option\fR...] [\fB\-o\fR \fIoutfile\fR] \fIinfile\fR... .PP Only the most useful options are listed here; see below for the remainder. .SH "DESCRIPTION" .IX Header "DESCRIPTION" The \fBgfortran\fR command supports all the options supported by the \&\fBgcc\fR command. Only options specific to \s-1GNU\s0 Fortran are documented here. .PP All \s-1GCC\s0 and \s-1GNU\s0 Fortran options are accepted both by \fBgfortran\fR and by \fBgcc\fR (as well as any other drivers built at the same time, such as \fBg++\fR), since adding \s-1GNU\s0 Fortran to the \s-1GCC\s0 distribution enables acceptance of \s-1GNU\s0 Fortran options by all of the relevant drivers. .PP In some cases, options have positive and negative forms; the negative form of \fB\-ffoo\fR would be \fB\-fno\-foo\fR. This manual documents only one of these two forms, whichever one is not the default. .SH "OPTIONS" .IX Header "OPTIONS" Here is a summary of all the options specific to \s-1GNU\s0 Fortran, grouped by type. Explanations are in the following sections. .IP "\fIFortran Language Options\fR" 4 .IX Item "Fortran Language Options" \&\fB\-fall\-intrinsics \-ffree\-form \-fno\-fixed\-form \&\-fdollar\-ok \-fimplicit\-none \-fmax\-identifier\-length \&\-std=\fR\fIstd\fR \fB\-fd\-lines\-as\-code \-fd\-lines\-as\-comments \&\-ffixed\-line\-length\-\fR\fIn\fR \fB\-ffixed\-line\-length\-none \&\-ffree\-line\-length\-\fR\fIn\fR \fB\-ffree\-line\-length\-none \&\-fdefault\-double\-8 \-fdefault\-integer\-8 \-fdefault\-real\-8 \&\-fcray\-pointer \-fopenmp \-fno\-range\-check \-fbackslash \-fmodule\-private\fR .IP "\fIError and Warning Options\fR" 4 .IX Item "Error and Warning Options" \&\fB\-fmax\-errors=\fR\fIn\fR \&\fB\-fsyntax\-only \-pedantic \-pedantic\-errors \&\-Wall \-Waliasing \-Wampersand \-Wcharacter\-truncation \-Wconversion \&\-Wimplicit\-interface \-Wline\-truncation \-Wnonstd\-intrinsics \-Wsurprising \&\-Wno\-tabs \-Wunderflow \-Wunused\-parameter\fR .IP "\fIDebugging Options\fR" 4 .IX Item "Debugging Options" \&\fB\-fdump\-parse\-tree \-ffpe\-trap=\fR\fIlist\fR \&\fB\-fdump\-core \-fbacktrace\fR .IP "\fIDirectory Options\fR" 4 .IX Item "Directory Options" \&\fB\-I\fR\fIdir\fR \fB\-J\fR\fIdir\fR \fB\-M\fR\fIdir\fR \fB\-fintrinsic\-modules\-path\fR \fIdir\fR .IP "\fILink Options\fR" 4 .IX Item "Link Options" \&\fB\-static\-libgfortran\fR .IP "\fIRuntime Options\fR" 4 .IX Item "Runtime Options" \&\fB\-fconvert=\fR\fIconversion\fR \fB\-frecord\-marker=\fR\fIlength\fR \&\fB\-fmax\-subrecord\-length=\fR\fIlength\fR \fB\-fsign\-zero\fR .IP "\fICode Generation Options\fR" 4 .IX Item "Code Generation Options" \&\fB\-fno\-automatic \-ff2c \-fno\-underscoring \&\-fsecond\-underscore \&\-fbounds\-check \-fmax\-stack\-var\-size=\fR\fIn\fR \&\fB\-fpack\-derived \-frepack\-arrays \-fshort\-enums \-fexternal\-blas \&\-fblas\-matmul\-limit=\fR\fIn\fR \fB\-frecursive \-finit\-local\-zero \&\-finit\-integer=\fR\fIn\fR \fB\-finit\-real=\fR\fI\fR \&\fB\-finit\-logical=\fR\fI\fR \fB\-finit\-character=\fR\fIn\fR .Sh "Options controlling Fortran dialect" .IX Subsection "Options controlling Fortran dialect" The following options control the details of the Fortran dialect accepted by the compiler: .IP "\fB\-ffree\-form\fR" 4 .IX Item "-ffree-form" .PD 0 .IP "\fB\-ffixed\-form\fR" 4 .IX Item "-ffixed-form" .PD 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. .IP "\fB\-fall\-intrinsics\fR" 4 .IX Item "-fall-intrinsics" Accept all of the intrinsic procedures provided in libgfortran without regard to the setting of \fB\-std\fR. In particular, this option can be quite useful with \fB\-std=f95\fR. Additionally, \&\fBgfortran\fR will ignore \fB\-Wnonstd\-intrinsics\fR. .IP "\fB\-fd\-lines\-as\-code\fR" 4 .IX Item "-fd-lines-as-code" .PD 0 .IP "\fB\-fd\-lines\-as\-comments\fR" 4 .IX Item "-fd-lines-as-comments" .PD Enable special treatment for lines beginning with \f(CW\*(C`d\*(C'\fR or \f(CW\*(C`D\*(C'\fR in fixed form sources. If the \fB\-fd\-lines\-as\-code\fR option is given they are treated as if the first column contained a blank. If the \&\fB\-fd\-lines\-as\-comments\fR option is given, they are treated as comment lines. .IP "\fB\-fdefault\-double\-8\fR" 4 .IX Item "-fdefault-double-8" Set the \f(CW\*(C`DOUBLE PRECISION\*(C'\fR type to an 8 byte wide type. .IP "\fB\-fdefault\-integer\-8\fR" 4 .IX 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. .IP "\fB\-fdefault\-real\-8\fR" 4 .IX Item "-fdefault-real-8" Set the default real type to an 8 byte wide type. Do nothing if this is already the default. .IP "\fB\-fdollar\-ok\fR" 4 .IX Item "-fdollar-ok" Allow \fB$\fR as a valid character in a symbol name. .IP "\fB\-fbackslash\fR" 4 .IX Item "-fbackslash" Change the interpretation of backslashes in string literals from a single backslash character to \*(L"C\-style\*(R" escape characters. The following combinations are expanded \ea, \eb, \ef, \en, \er, \et, \&\ev, \e, and \e0 to the \s-1ASCII\s0 characters alert, backspace, form feed, newline, carriage return, horizontal tab, vertical tab, backslash, and \s-1NUL\s0, respectively. All other combinations of a character preceded by \e are unexpanded. .IP "\fB\-fmodule\-private\fR" 4 .IX Item "-fmodule-private" Set the default accessibility of module entities to \f(CW\*(C`PRIVATE\*(C'\fR. Use-associated entities will not be accessible unless they are explicitly declared as \f(CW\*(C`PUBLIC\*(C'\fR. .IP "\fB\-ffixed\-line\-length\-\fR\fIn\fR" 4 .IX Item "-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. .Sp Popular values for \fIn\fR include 72 (the standard and the default), 80 (card image), and 132 (corresponding to \*(L"extended-source\*(R" options in some popular compilers). \&\fIn\fR may also be \fBnone\fR, meaning that the entire line is meaningful and that continued character constants never have implicit spaces appended to them to fill out the line. \&\fB\-ffixed\-line\-length\-0\fR means the same thing as \&\fB\-ffixed\-line\-length\-none\fR. .IP "\fB\-ffree\-line\-length\-\fR\fIn\fR" 4 .IX Item "-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. \&\fIn\fR may be \fBnone\fR, meaning that the entire line is meaningful. \&\fB\-ffree\-line\-length\-0\fR means the same thing as \&\fB\-ffree\-line\-length\-none\fR. .IP "\fB\-fmax\-identifier\-length=\fR\fIn\fR" 4 .IX Item "-fmax-identifier-length=n" Specify the maximum allowed identifier length. Typical values are 31 (Fortran 95) and 63 (Fortran 2003). .IP "\fB\-fimplicit\-none\fR" 4 .IX Item "-fimplicit-none" Specify that no implicit typing is allowed, unless overridden by explicit \&\f(CW\*(C`IMPLICIT\*(C'\fR statements. This is the equivalent of adding \&\f(CW\*(C`implicit none\*(C'\fR to the start of every procedure. .IP "\fB\-fcray\-pointer\fR" 4 .IX Item "-fcray-pointer" Enable the Cray pointer extension, which provides C\-like pointer functionality. .IP "\fB\-fopenmp\fR" 4 .IX Item "-fopenmp" Enable the OpenMP extensions. This includes OpenMP \f(CW\*(C`!$omp\*(C'\fR directives in free form and \f(CW\*(C`c$omp\*(C'\fR, \f(CW*$omp\fR and \f(CW\*(C`!$omp\*(C'\fR directives in fixed form, \&\f(CW\*(C`!$\*(C'\fR conditional compilation sentinels in free form and \f(CW\*(C`c$\*(C'\fR, \f(CW\*(C`*$\*(C'\fR and \f(CW\*(C`!$\*(C'\fR sentinels in fixed form, and when linking arranges for the OpenMP runtime library to be linked in. The option \fB\-fopenmp\fR implies \fB\-frecursive\fR. .IP "\fB\-fno\-range\-check\fR" 4 .IX Item "-fno-range-check" Disable range checking on results of simplification of constant expressions during compilation. For example, \s-1GNU\s0 Fortran will give an error at compile time when simplifying \f(CW\*(C`a = 1. / 0\*(C'\fR. With this option, no error will be given and \f(CW\*(C`a\*(C'\fR will be assigned the value \f(CW\*(C`+Infinity\*(C'\fR. If an expression evaluates to a value outside of the relevant range of [\f(CW\*(C`\-HUGE()\*(C'\fR:\f(CW\*(C`HUGE()\*(C'\fR], then the expression will be replaced by \f(CW\*(C`\-Inf\*(C'\fR or \f(CW\*(C`+Inf\*(C'\fR as appropriate. Similarly, \f(CW\*(C`DATA i/Z\*(AqFFFFFFFF\*(Aq/\*(C'\fR will result in an integer overflow on most systems, but with \fB\-fno\-range\-check\fR the value will \&\*(L"wrap around\*(R" and \f(CW\*(C`i\*(C'\fR will be initialized to \-1 instead. .IP "\fB\-std=\fR\fIstd\fR" 4 .IX Item "-std=std" Specify the standard to which the program is expected to conform, which may be one of \fBf95\fR, \fBf2003\fR, \fBgnu\fR, or \fBlegacy\fR. The default value for \fIstd\fR is \fBgnu\fR, which specifies a superset of the Fortran 95 standard that includes all of the extensions supported by \s-1GNU\s0 Fortran, although warnings will be given for obsolete extensions not recommended for use in new code. The \fBlegacy\fR value is equivalent but without the warnings for obsolete extensions, and may be useful for old non-standard programs. The \fBf95\fR and \&\fBf2003\fR values specify strict conformance to the Fortran 95 and Fortran 2003 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. .Sh "Options to request or suppress errors and warnings" .IX Subsection "Options to request or suppress errors and warnings" Errors are diagnostic messages that report that the \s-1GNU\s0 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. .PP 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 \fB\-Werror\fR is specified, they do not prevent compilation of the program. .PP You can request many specific warnings with options beginning \fB\-W\fR, for example \fB\-Wimplicit\fR to request warnings on implicit declarations. Each of these specific warning options also has a negative form beginning \fB\-Wno\-\fR to turn off warnings; for example, \fB\-Wno\-implicit\fR. This manual lists only one of the two forms, whichever is not the default. .PP These options control the amount and kinds of errors and warnings produced by \s-1GNU\s0 Fortran: .IP "\fB\-fmax\-errors=\fR\fIn\fR" 4 .IX Item "-fmax-errors=n" Limits the maximum number of error messages to \fIn\fR, at which point \&\s-1GNU\s0 Fortran bails out rather than attempting to continue processing the source code. If \fIn\fR is 0, there is no limit on the number of error messages produced. .IP "\fB\-fsyntax\-only\fR" 4 .IX Item "-fsyntax-only" Check the code for syntax errors, but don't actually compile it. This will generate module files for each module present in the code, but no other output file. .IP "\fB\-pedantic\fR" 4 .IX Item "-pedantic" Issue warnings for uses of extensions to Fortran 95. \&\fB\-pedantic\fR also applies to C\-language constructs where they occur in \s-1GNU\s0 Fortran source files, such as use of \fB\ee\fR in a character constant within a directive like \f(CW\*(C`#include\*(C'\fR. .Sp Valid Fortran 95 programs should compile properly with or without this option. However, without this option, certain \s-1GNU\s0 extensions and traditional Fortran features are supported as well. With this option, many of them are rejected. .Sp Some users try to use \fB\-pedantic\fR 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 \s-1GNU\s0 Fortran in this area are welcome. .Sp This should be used in conjunction with \fB\-std=f95\fR or \&\fB\-std=f2003\fR. .IP "\fB\-pedantic\-errors\fR" 4 .IX Item "-pedantic-errors" Like \fB\-pedantic\fR, except that errors are produced rather than warnings. .IP "\fB\-Wall\fR" 4 .IX Item "-Wall" Enables commonly used warning options pertaining to usage that we recommend avoiding and that we believe are easy to avoid. This currently includes \fB\-Waliasing\fR, \&\fB\-Wampersand\fR, \fB\-Wsurprising\fR, \fB\-Wnonstd\-intrinsics\fR, \&\fB\-Wno\-tabs\fR, and \fB\-Wline\-truncation\fR. .IP "\fB\-Waliasing\fR" 4 .IX Item "-Waliasing" Warn about possible aliasing of dummy arguments. Specifically, it warns if the same actual argument is associated with a dummy argument with \&\f(CW\*(C`INTENT(IN)\*(C'\fR and a dummy argument with \f(CW\*(C`INTENT(OUT)\*(C'\fR in a call with an explicit interface. .Sp The following example will trigger the warning. .Sp .Vb 7 \& interface \& subroutine bar(a,b) \& integer, intent(in) :: a \& integer, intent(out) :: b \& end subroutine \& end interface \& integer :: a \& \& call bar(a,a) .Ve .IP "\fB\-Wampersand\fR" 4 .IX Item "-Wampersand" Warn about missing ampersand in continued character constants. The warning is given with \fB\-Wampersand\fR, \fB\-pedantic\fR, \fB\-std=f95\fR, and \&\fB\-std=f2003\fR. Note: With no ampersand given in a continued character constant, \s-1GNU\s0 Fortran assumes continuation at the first non-comment, non-whitespace character after the ampersand that initiated the continuation. .IP "\fB\-Wcharacter\-truncation\fR" 4 .IX Item "-Wcharacter-truncation" Warn when a character assignment will truncate the assigned string. .IP "\fB\-Wconversion\fR" 4 .IX Item "-Wconversion" Warn about implicit conversions between different types. .IP "\fB\-Wimplicit\-interface\fR" 4 .IX Item "-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. .IP "\fB\-Wnonstd\-intrinsics\fR" 4 .IX Item "-Wnonstd-intrinsics" Warn if the user tries to use an intrinsic that does not belong to the standard the user has chosen via the \fB\-std\fR option. .IP "\fB\-Wsurprising\fR" 4 .IX Item "-Wsurprising" Produce a warning when \*(L"suspicious\*(R" code constructs are encountered. While technically legal these usually indicate that an error has been made. .Sp This currently produces a warning under the following circumstances: .RS 4 .IP "\(bu" 4 An \s-1INTEGER\s0 \s-1SELECT\s0 construct has a \s-1CASE\s0 that can never be matched as its lower value is greater than its upper value. .IP "\(bu" 4 A \s-1LOGICAL\s0 \s-1SELECT\s0 construct has three \s-1CASE\s0 statements. .IP "\(bu" 4 A \s-1TRANSFER\s0 specifies a source that is shorter than the destination. .RE .RS 4 .RE .IP "\fB\-Wtabs\fR" 4 .IX Item "-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. \fB\-Wno\-tabs\fR will cause a warning to be issued if a tab is encountered. Note, \fB\-Wno\-tabs\fR is active for \fB\-pedantic\fR, \fB\-std=f95\fR, \fB\-std=f2003\fR, and \fB\-Wall\fR. .IP "\fB\-Wunderflow\fR" 4 .IX Item "-Wunderflow" Produce a warning when numerical constant expressions are encountered, which yield an \s-1UNDERFLOW\s0 during compilation. .IP "\fB\-Wunused\-parameter\fR" 4 .IX Item "-Wunused-parameter" Contrary to \fBgcc\fR's meaning of \fB\-Wunused\-parameter\fR, \&\fBgfortran\fR's implementation of this option does not warn about unused dummy arguments, but about unused \f(CW\*(C`PARAMETER\*(C'\fR values. \&\fB\-Wunused\-parameter\fR is not included in \fB\-Wall\fR but is implied by \fB\-Wall \-Wextra\fR. .IP "\fB\-Werror\fR" 4 .IX Item "-Werror" Turns all warnings into errors. .PP Some of these have no effect when compiling programs written in Fortran. .Sh "Options for debugging your program or \s-1GNU\s0 Fortran" .IX Subsection "Options for debugging your program or GNU Fortran" \&\s-1GNU\s0 Fortran has various special options that are used for debugging either your program or the \s-1GNU\s0 Fortran compiler. .IP "\fB\-fdump\-parse\-tree\fR" 4 .IX Item "-fdump-parse-tree" Output the internal parse tree before starting code generation. Only really useful for debugging the \s-1GNU\s0 Fortran compiler itself. .IP "\fB\-ffpe\-trap=\fR\fIlist\fR" 4 .IX Item "-ffpe-trap=list" Specify a list of \s-1IEEE\s0 exceptions when a Floating Point Exception (\s-1FPE\s0) should be raised. On most systems, this will result in a \s-1SIGFPE\s0 signal being sent and the program being interrupted, producing a core file useful for debugging. \fIlist\fR is a (possibly empty) comma-separated list of the following \s-1IEEE\s0 exceptions: \fBinvalid\fR (invalid floating point operation, such as \f(CW\*(C`SQRT(\-1.0)\*(C'\fR), \fBzero\fR (division by zero), \fBoverflow\fR (overflow in a floating point operation), \&\fBunderflow\fR (underflow in a floating point operation), \&\fBprecision\fR (loss of precision during operation) and \fBdenormal\fR (operation produced a denormal value). .Sp Some of the routines in the Fortran runtime library, like \&\fB\s-1CPU_TIME\s0\fR, are likely to to trigger floating point exceptions when \&\f(CW\*(C`ffpe\-trap=precision\*(C'\fR is used. For this reason, the use of \&\f(CW\*(C`ffpe\-trap=precision\*(C'\fR is not recommended. .IP "\fB\-fbacktrace\fR" 4 .IX Item "-fbacktrace" Specify that, when a runtime error is encountered or a deadly signal is emitted (segmentation fault, illegal instruction, bus error or floating-point exception), the Fortran runtime library should output a backtrace of the error. This option only has influence for compilation of the Fortran main program. .IP "\fB\-fdump\-core\fR" 4 .IX Item "-fdump-core" Request that a core-dump file is written to disk when a runtime error is encountered on systems that support core dumps. This option is only effective for the compilation of the Fortran main program. .Sh "Options for directory search" .IX Subsection "Options for directory search" These options affect how \s-1GNU\s0 Fortran searches for files specified by the \f(CW\*(C`INCLUDE\*(C'\fR directive and where it searches for previously compiled modules. .PP It also affects the search paths used by \fBcpp\fR when used to preprocess Fortran source. .IP "\fB\-I\fR\fIdir\fR" 4 .IX Item "-Idir" These affect interpretation of the \f(CW\*(C`INCLUDE\*(C'\fR directive (as well as of the \f(CW\*(C`#include\*(C'\fR directive of the \fBcpp\fR preprocessor). .Sp Also note that the general behavior of \fB\-I\fR and \&\f(CW\*(C`INCLUDE\*(C'\fR is pretty much the same as of \fB\-I\fR with \&\f(CW\*(C`#include\*(C'\fR in the \fBcpp\fR preprocessor, with regard to looking for \fIheader.gcc\fR files and other such things. .Sp This path is also used to search for \fI.mod\fR files when previously compiled modules are required by a \f(CW\*(C`USE\*(C'\fR statement. .IP "\fB\-M\fR\fIdir\fR" 4 .IX Item "-Mdir" .PD 0 .IP "\fB\-J\fR\fIdir\fR" 4 .IX Item "-Jdir" .PD This option specifies where to put \fI.mod\fR files for compiled modules. It is also added to the list of directories to searched by an \f(CW\*(C`USE\*(C'\fR statement. .Sp The default is the current directory. .Sp \&\fB\-J\fR is an alias for \fB\-M\fR to avoid conflicts with existing \&\s-1GCC\s0 options. .IP "\fB\-fintrinsic\-modules\-path\fR \fIdir\fR" 4 .IX Item "-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. .Sh "Influencing the linking step" .IX Subsection "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. .IP "\fB\-static\-libgfortran\fR" 4 .IX Item "-static-libgfortran" On systems that provide \fIlibgfortran\fR as a shared and a static library, this option forces the use of the static version. If no shared version of \fIlibgfortran\fR was built when the compiler was configured, this option has no effect. .Sh "Influencing runtime behavior" .IX Subsection "Influencing runtime behavior" These options affect the runtime behavior of programs compiled with \s-1GNU\s0 Fortran. .IP "\fB\-fconvert=\fR\fIconversion\fR" 4 .IX Item "-fconvert=conversion" Specify the representation of data for unformatted files. Valid values for conversion are: \fBnative\fR, the default; \fBswap\fR, swap between big\- and little-endian; \fBbig-endian\fR, use big-endian representation for unformatted files; \fBlittle-endian\fR, use little-endian representation for unformatted files. .Sp \&\fIThis option has an effect only when used in the main program. The \f(CI\*(C`CONVERT\*(C'\fI specifier and the \s-1GFORTRAN_CONVERT_UNIT\s0 environment variable override the default specified by \f(BI\-fconvert\fI.\fR .IP "\fB\-frecord\-marker=\fR\fIlength\fR" 4 .IX Item "-frecord-marker=length" Specify the length of record markers for unformatted files. Valid values for \fIlength\fR are 4 and 8. Default is 4. \&\fIThis is different from previous versions of\fR \fBgfortran\fR, 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 \fBgfortran\fR, use \fB\-frecord\-marker=8\fR. .IP "\fB\-fmax\-subrecord\-length=\fR\fIlength\fR" 4 .IX Item "-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. .IP "\fB\-fsign\-zero\fR" 4 .IX Item "-fsign-zero" When writing zero values, show the negative sign if the sign bit is set. \&\f(CW\*(C`fno\-sign\-zero\*(C'\fR does not print the negative sign of zero values for compatibility with F77. Default behavior is to show the negative sign. .Sh "Options for code generation conventions" .IX Subsection "Options for code generation conventions" These machine-independent options control the interface conventions used in code generation. .PP Most of them have both positive and negative forms; the negative form of \fB\-ffoo\fR would be \fB\-fno\-foo\fR. 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 \fBno\-\fR or adding it. .IP "\fB\-fno\-automatic\fR" 4 .IX Item "-fno-automatic" Treat each program unit (except those marked as \s-1RECURSIVE\s0) as if the \&\f(CW\*(C`SAVE\*(C'\fR 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 \fB\-static\fR or \fB\-save\fR.) The default, which is \fB\-fautomatic\fR, uses the stack for local variables smaller than the value given by \fB\-fmax\-stack\-var\-size\fR. Use the option \fB\-frecursive\fR to use no static memory. .IP "\fB\-ff2c\fR" 4 .IX Item "-ff2c" Generate code designed to be compatible with code generated by \fBg77\fR and \fBf2c\fR. .Sp The calling conventions used by \fBg77\fR (originally implemented in \fBf2c\fR) require functions that return type default \f(CW\*(C`REAL\*(C'\fR to actually return the C type \f(CW\*(C`double\*(C'\fR, and functions that return type \f(CW\*(C`COMPLEX\*(C'\fR to return the values via an extra argument in the calling sequence that points to where to store the return value. Under the default \s-1GNU\s0 calling conventions, such functions simply return their results as they would in \s-1GNU\s0 C\-\-\-default \f(CW\*(C`REAL\*(C'\fR functions return the C type \f(CW\*(C`float\*(C'\fR, and \&\f(CW\*(C`COMPLEX\*(C'\fR functions return the \s-1GNU\s0 C type \f(CW\*(C`complex\*(C'\fR. Additionally, this option implies the \fB\-fsecond\-underscore\fR option, unless \fB\-fno\-second\-underscore\fR is explicitly requested. .Sp This does not affect the generation of code that interfaces with the \fBlibgfortran\fR library. .Sp \&\fICaution:\fR It is not a good idea to mix Fortran code compiled with \&\fB\-ff2c\fR with code compiled with the default \fB\-fno\-f2c\fR calling conventions as, calling \f(CW\*(C`COMPLEX\*(C'\fR or default \f(CW\*(C`REAL\*(C'\fR functions between program parts which were compiled with different calling conventions will break at execution time. .Sp \&\fICaution:\fR This will break code which passes intrinsic functions of type default \f(CW\*(C`REAL\*(C'\fR or \f(CW\*(C`COMPLEX\*(C'\fR as actual arguments, as the library implementations use the \fB\-fno\-f2c\fR calling conventions. .IP "\fB\-fno\-underscoring\fR" 4 .IX Item "-fno-underscoring" Do not transform names of entities specified in the Fortran source file by appending underscores to them. .Sp With \fB\-funderscoring\fR in effect, \s-1GNU\s0 Fortran appends one underscore to external names with no underscores. This is done to ensure compatibility with code produced by many \s-1UNIX\s0 Fortran compilers. .Sp \&\fICaution\fR: The default behavior of \s-1GNU\s0 Fortran is incompatible with \fBf2c\fR and \fBg77\fR, please use the \&\fB\-ff2c\fR option if you want object files compiled with \&\s-1GNU\s0 Fortran to be compatible with object code created with these tools. .Sp Use of \fB\-fno\-underscoring\fR is not recommended unless you are experimenting with issues such as integration of \s-1GNU\s0 Fortran into existing system environments (vis\-@`{a}\-vis existing libraries, tools, and so on). .Sp For example, with \fB\-funderscoring\fR, and assuming other defaults like \&\fB\-fcase\-lower\fR and that \f(CW\*(C`j()\*(C'\fR and \f(CW\*(C`max_count()\*(C'\fR are external functions while \f(CW\*(C`my_var\*(C'\fR and \f(CW\*(C`lvar\*(C'\fR are local variables, a statement like .Sp .Vb 1 \& I = J() + MAX_COUNT (MY_VAR, LVAR) .Ve .Sp is implemented as something akin to: .Sp .Vb 1 \& i = j_() + max_count_\|_(&my_var_\|_, &lvar); .Ve .Sp With \fB\-fno\-underscoring\fR, the same statement is implemented as: .Sp .Vb 1 \& i = j() + max_count(&my_var, &lvar); .Ve .Sp Use of \fB\-fno\-underscoring\fR allows direct specification of user-defined names while debugging and when interfacing \s-1GNU\s0 Fortran code with other languages. .Sp Note that just because the names match does \fInot\fR mean that the interface implemented by \s-1GNU\s0 Fortran for an external name matches the interface implemented by some other language for that same name. That is, getting code produced by \s-1GNU\s0 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. .Sp Also, note that with \fB\-fno\-underscoring\fR, 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. .Sp In future versions of \s-1GNU\s0 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. .IP "\fB\-fsecond\-underscore\fR" 4 .IX Item "-fsecond-underscore" By default, \s-1GNU\s0 Fortran appends an underscore to external names. If this option is used \s-1GNU\s0 Fortran appends two underscores to names with underscores and one underscore to external names with no underscores. \s-1GNU\s0 Fortran also appends two underscores to internal names with underscores to avoid naming collisions with external names. .Sp This option has no effect if \fB\-fno\-underscoring\fR is in effect. It is implied by the \fB\-ff2c\fR option. .Sp Otherwise, with this option, an external name such as \f(CW\*(C`MAX_COUNT\*(C'\fR is implemented as a reference to the link-time external symbol \&\f(CW\*(C`max_count_\|_\*(C'\fR, instead of \f(CW\*(C`max_count_\*(C'\fR. This is required for compatibility with \fBg77\fR and \fBf2c\fR, and is implied by use of the \fB\-ff2c\fR option. .IP "\fB\-fbounds\-check\fR" 4 .IX Item "-fbounds-check" Enable generation of run-time checks for array subscripts and against the declared minimum and maximum values. It also checks array indices for assumed and deferred shape arrays against the actual allocated bounds. .Sp Some checks require that \fB\-fbounds\-check\fR is set for the compilation of the main program. .Sp In the future this may also include other forms of checking, e.g., checking substring references. .IP "\fB\-fmax\-stack\-var\-size=\fR\fIn\fR" 4 .IX Item "-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 \s-1RECURSIVE\s0). Use the option \fB\-frecursive\fR to allow for recursive procedures which do not have a \s-1RECURSIVE\s0 attribute or for parallel programs. Use \fB\-fno\-automatic\fR to never use the stack. .Sp This option currently only affects local arrays declared with constant bounds, and may not apply to all character variables. Future versions of \s-1GNU\s0 Fortran may improve this behavior. .Sp The default value for \fIn\fR is 32768. .IP "\fB\-fpack\-derived\fR" 4 .IX Item "-fpack-derived" This option tells \s-1GNU\s0 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. .IP "\fB\-frepack\-arrays\fR" 4 .IX Item "-frepack-arrays" In some circumstances \s-1GNU\s0 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. .Sp 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. .IP "\fB\-fshort\-enums\fR" 4 .IX Item "-fshort-enums" This option is provided for interoperability with C code that was compiled with the \fB\-fshort\-enums\fR option. It will make \&\s-1GNU\s0 Fortran choose the smallest \f(CW\*(C`INTEGER\*(C'\fR kind a given enumerator set will fit in, and give all its enumerators this kind. .IP "\fB\-fexternal\-blas\fR" 4 .IX Item "-fexternal-blas" This option will make \fBgfortran\fR generate calls to \s-1BLAS\s0 functions for some matrix operations like \f(CW\*(C`MATMUL\*(C'\fR, instead of using our own algorithms, if the size of the matrices involved is larger than a given limit (see \fB\-fblas\-matmul\-limit\fR). This may be profitable if an optimized vendor \s-1BLAS\s0 library is available. The \s-1BLAS\s0 library will have to be specified at link time. .IP "\fB\-fblas\-matmul\-limit=\fR\fIn\fR" 4 .IX Item "-fblas-matmul-limit=n" Only significant when \fB\-fexternal\-blas\fR is in effect. Matrix multiplication of matrices with size larger than (or equal to) \fIn\fR will be performed by calls to \s-1BLAS\s0 functions, while others will be handled by \fBgfortran\fR 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. .Sp The default value for \fIn\fR is 30. .IP "\fB\-frecursive\fR" 4 .IX Item "-frecursive" Allow indirect recursion by forcing all local arrays to be allocated on the stack. This flag cannot be used together with \&\fB\-fmax\-stack\-var\-size=\fR or \fB\-fno\-automatic\fR. .IP "\fB\-finit\-local\-zero\fR" 4 .IX Item "-finit-local-zero" .PD 0 .IP "\fB\-finit\-integer=\fR\fIn\fR" 4 .IX Item "-finit-integer=n" .IP "\fB\-finit\-real=\fR\fI\fR\fB \fR" 4 .IX Item "-finit-real= " .IP "\fB\-finit\-logical=\fR\fI\fR" 4 .IX Item "-finit-logical=" .IP "\fB\-finit\-character=\fR\fIn\fR" 4 .IX Item "-finit-character=n" .PD The \fB\-finit\-local\-zero\fR option instructs the compiler to initialize local \f(CW\*(C`INTEGER\*(C'\fR, \f(CW\*(C`REAL\*(C'\fR, and \f(CW\*(C`COMPLEX\*(C'\fR variables to zero, \f(CW\*(C`LOGICAL\*(C'\fR variables to false, and \&\f(CW\*(C`CHARACTER\*(C'\fR variables to a string of null bytes. Finer-grained initialization options are provided by the \&\fB\-finit\-integer=\fR\fIn\fR, \&\fB\-finit\-real=\fR\fI\fR (which also initializes the real and imaginary parts of local \f(CW\*(C`COMPLEX\*(C'\fR variables), \&\fB\-finit\-logical=\fR\fI\fR, and \&\fB\-finit\-character=\fR\fIn\fR (where \fIn\fR is an \s-1ASCII\s0 character value) options. These options do not initialize components of derived type variables, nor do they initialize variables that appear in an \&\f(CW\*(C`EQUIVALENCE\*(C'\fR statement. (This limitation may be removed in future releases). .Sp Note that the \fB\-finit\-real=nan\fR option initializes \f(CW\*(C`REAL\*(C'\fR and \f(CW\*(C`COMPLEX\*(C'\fR variables with a quiet NaN. .SH "ENVIRONMENT" .IX Header "ENVIRONMENT" The \fBgfortran\fR compiler currently does not make use of any environment variables to control its operation above and beyond those that affect the operation of \fBgcc\fR. .SH "BUGS" .IX Header "BUGS" For instructions on reporting bugs, see <\fBhttp://gcc.gnu.org/bugs.html\fR>. .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fIgpl\fR\|(7), \fIgfdl\fR\|(7), \fIfsf\-funding\fR\|(7), \&\fIcpp\fR\|(1), \fIgcov\fR\|(1), \fIgcc\fR\|(1), \fIas\fR\|(1), \fIld\fR\|(1), \fIgdb\fR\|(1), \fIadb\fR\|(1), \fIdbx\fR\|(1), \fIsdb\fR\|(1) and the Info entries for \fIgcc\fR, \fIcpp\fR, \fIgfortran\fR, \fIas\fR, \&\fIld\fR, \fIbinutils\fR and \fIgdb\fR. .SH "AUTHOR" .IX Header "AUTHOR" See the Info entry for \fBgfortran\fR for contributors to \s-1GCC\s0 and \&\s-1GNU\s0 Fortran. .SH "COPYRIGHT" .IX Header "COPYRIGHT" Copyright (c) 2004, 2005, 2006, 2007 Free Software Foundation, Inc. .PP Permission is granted to copy, distribute and/or modify this document under the terms of the \s-1GNU\s0 Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with the Invariant Sections being \*(L"\s-1GNU\s0 General Public License\*(R" and \*(L"Funding Free Software\*(R", 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 \fIgfdl\fR\|(7) man page. .PP (a) The \s-1FSF\s0's Front-Cover Text is: .PP .Vb 1 \& A GNU Manual .Ve .PP (b) The \s-1FSF\s0's Back-Cover Text is: .PP .Vb 3 \& 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. .Ve