\input texinfo @c -*-texinfo-*- @c %**start of header @setfilename gfortran.info @set copyrights-gfortran 1999-2005 @include gcc-common.texi @settitle The GNU Fortran 95 Compiler @c Create a separate index for command line options @defcodeindex op @c Merge the standard indexes into a single one. @syncodeindex fn cp @syncodeindex vr cp @syncodeindex ky cp @syncodeindex pg cp @syncodeindex tp cp @c %**end of header @c Use with @@smallbook. @c %** start of document @c Cause even numbered pages to be printed on the left hand side of @c the page and odd numbered pages to be printed on the right hand @c side of the page. Using this, you can print on both sides of a @c sheet of paper and have the text on the same part of the sheet. @c The text on right hand pages is pushed towards the right hand @c margin and the text on left hand pages is pushed toward the left @c hand margin. @c (To provide the reverse effect, set bindingoffset to -0.75in.) @c @tex @c \global\bindingoffset=0.75in @c \global\normaloffset =0.75in @c @end tex @copying Copyright @copyright{} @value{copyrights-gfortran} 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 1.1 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 section entitled ``GNU Free Documentation License''. (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. @end copying @ifinfo @dircategory Programming @direntry * gfortran: (gfortran). The GNU Fortran 95 Compiler. @end direntry This file documents the use and the internals of the GNU Fortran 95 compiler, (@command{gfortran}). Published by the Free Software Foundation 51 Franklin Street, Fifth Floor Boston, MA 02110-1301 USA @insertcopying @end ifinfo @setchapternewpage odd @titlepage @title Using GNU Fortran 95 @sp 2 @center The gfortran team @page @vskip 0pt plus 1filll For the @value{version-GCC} Version* @sp 1 Published by the Free Software Foundation @* 51 Franklin Street, Fifth Floor@* Boston, MA 02110-1301, USA@* @c Last printed ??ber, 19??.@* @c Printed copies are available for $? each.@* @c ISBN ??? @sp 1 @insertcopying @end titlepage @summarycontents @contents @page @node Top @top Introduction @cindex Introduction This manual documents the use of @command{gfortran}, the GNU Fortran 95 compiler. You can find in this manual how to invoke @command{gfortran}, as well as its features and incompatibilities. @ifset DEVELOPMENT @emph{Warning:} This document, and the compiler it describes, are still under development. While efforts are made to keep it up-to-date, it might not accurately reflect the status of the most recent @command{gfortran}. @end ifset @comment @comment When you add a new menu item, please keep the right hand @comment aligned to the same column. Do not use tabs. This provides @comment better formatting. @comment @menu * Getting Started:: What you should know about @command{gfortran}. * GFORTRAN and GCC:: You can compile Fortran, C, or other programs. * GFORTRAN and G77:: Why we chose to start from scratch. * Invoking GFORTRAN:: Command options supported by @command{gfortran}. * Project Status:: Status of @command{gfortran}, roadmap, proposed extensions. * Contributing:: How you can help. * Standards:: Standards supported by @command{gfortran} * Runtime:: Influencing runtime behavior with environment variables. * Extensions:: Language extensions implemented by @command{gfortran} * Intrinsic Procedures:: Intrinsic procedures supported by @command{gfortran} * Copying:: GNU General Public License says how you can copy and share GNU Fortran. * GNU Free Documentation License:: How you can copy and share this manual. * Funding:: How to help assure continued work for free software. * Index:: Index of this documentation. @end menu @c --------------------------------------------------------------------- @c Getting Started @c --------------------------------------------------------------------- @node Getting Started @chapter Getting Started Gfortran is the GNU Fortran 95 compiler front end, designed initially as a free replacement for, or alternative to, the unix @command{f95} command; @command{gfortran} is the command you'll use to invoke the compiler. Gfortran is still in an early state of development. @command{gfortran} can generate code for most constructs and expressions, but much work remains to be done. When @command{gfortran} is finished, it will do everything you expect from any decent compiler: @itemize @bullet @item Read a user's program, stored in a file and containing instructions written in Fortran 77, Fortran 90 or Fortran 95. This file contains @dfn{source code}. @item Translate the user's program into instructions a computer can carry out more quickly than it takes to translate the instructions in the first place. The result after compilation of a program is @dfn{machine code}, code designed to be efficiently translated and processed by a machine such as your computer. Humans usually aren't as good writing machine code as they are at writing Fortran (or C++, Ada, or Java), because is easy to make tiny mistakes writing machine code. @item Provide the user with information about the reasons why the compiler is unable to create a binary from the source code. Usually this will be the case if the source code is flawed. When writing Fortran, it is easy to make big mistakes. The Fortran 90 requires that the compiler can point out mistakes to the user. An incorrect usage of the language causes an @dfn{error message}. The compiler will also attempt to diagnose cases where the user's program contains a correct usage of the language, but instructs the computer to do something questionable. This kind of diagnostics message is called a @dfn{warning message}. @item Provide optional information about the translation passes from the source code to machine code. This can help a user of the compiler to find the cause of certain bugs which may not be obvious in the source code, but may be more easily found at a lower level compiler output. It also helps developers to find bugs in the compiler itself. @item Provide information in the generated machine code that can make it easier to find bugs in the program (using a debugging tool, called a @dfn{debugger}, such as the GNU Debugger @command{gdb}). @item Locate and gather machine code already generated to perform actions requested by statements in the user's program. This machine code is organized into @dfn{modules} and is located and @dfn{linked} to the user program. @end itemize Gfortran consists of several components: @itemize @bullet @item A version of the @command{gcc} command (which also might be installed as the system's @command{cc} command) that also understands and accepts Fortran source code. The @command{gcc} command is the @dfn{driver} program for all the languages in the GNU Compiler Collection (GCC); With @command{gcc}, you can compile the source code of any language for which a front end is available in GCC. @item The @command{gfortran} command itself, which also might be installed as the system's @command{f95} command. @command{gfortran} is just another driver program, but specifically for the Fortran 95 compiler only. The difference with @command{gcc} is that @command{gfortran} will automatically link the correct libraries to your program. @item A collection of run-time libraries. These libraries contain the machine code needed to support capabilities of the Fortran language that are not directly provided by the machine code generated by the @command{gfortran} compilation phase, such as intrinsic functions and subroutines, and routines for interaction with files and the operating system. @c and mechanisms to spawn, @c unleash and pause threads in parallelized code. @item The Fortran compiler itself, (@command{f951}). This is the gfortran parser and code generator, linked to and interfaced with the GCC backend library. @command{f951} ``translates'' the source code to assembler code. You would typically not use this program directly; instead, the @command{gcc} or @command{gfortran} driver programs will call it for you. @end itemize @c --------------------------------------------------------------------- @c GFORTRAN and GCC @c --------------------------------------------------------------------- @node GFORTRAN and GCC @chapter GFORTRAN and GCC @cindex GNU Compiler Collection GCC used to be the GNU ``C'' Compiler, but is now known as the @dfn{GNU Compiler Collection}. GCC provides the GNU system with a very versatile compiler middle end (shared optimization passes), and back ends (code generators) for many different computer architectures and operating systems. The code of the middle end and back end are shared by all compiler front ends that are in the GNU Compiler Collection. A GCC front end is essentially a source code parser and an intermediate code generator. The code generator translates the semantics of the source code into a language independent form called @dfn{GENERIC}. The parser takes a source file written in a particular computer language, reads and parses it, and tries to make sure that the source code conforms to the language rules. Once the correctness of a program has been established, the compiler will build a data structure known as the @dfn{Abstract Syntax tree}, or just @dfn{AST} or ``tree'' for short. This data structure represents the whole program or a subroutine or a function. The ``tree'' is passed to the GCC middle end, which will perform optimization passes on it. The optimized AST is then handed off too the back end which assembles the program unit. Different phases in this translation process can be, and in fact @emph{are} merged in many compiler front ends. GNU Fortran 95 has a strict separation between the parser and code generator. The goal of the gfortran project is to build a new front end for GCC. Specifically, a Fortran 95 front end. In a non-gfortran installation, @command{gcc} will not be able to compile Fortran 95 source code (only the ``C'' front end has to be compiled if you want to build GCC, all other languages are optional). If you build GCC with gfortran, @command{gcc} will recognize @file{.f/.f90/.f95} source files and accepts Fortran 95 specific command line options. @c --------------------------------------------------------------------- @c GFORTRAN and G77 @c --------------------------------------------------------------------- @node GFORTRAN and G77 @chapter GFORTRAN and G77 @cindex Fortran 77 @cindex G77 Why do we write a compiler front end from scratch? There's a fine Fortran 77 compiler in the GNU Compiler Collection that accepts some features of the Fortran 90 standard as extensions. Why not start from there and revamp it? One of the reasons is that Craig Burley, the author of G77, has decided to stop working on the G77 front end. On @uref{http://world.std.com/~burley/g77-why.html, Craig explains the reasons for his decision to stop working on G77} in one of the pages in his homepage. Among the reasons is a lack of interest in improvements to @command{g77}. Users appear to be quite satisfied with @command{g77} as it is. While @command{g77} is still being maintained (by Toon Moene), it is unlikely that sufficient people will be willing to completely rewrite the existing code. But there are other reasons to start from scratch. Many people, including Craig Burley, no longer agreed with certain design decisions in the G77 front end. Also, the interface of @command{g77} to the back end is written in a style which is confusing and not up to date on recommended practice. In fact, a full rewrite had already been planned for GCC 3.0. When Craig decided to stop, it just seemed to be a better idea to start a new project from scratch, because it was expected to be easier to maintain code we develop ourselves than to do a major overhaul of @command{g77} first, and then build a Fortran 95 compiler out of it. @include invoke.texi @c --------------------------------------------------------------------- @c Project Status @c --------------------------------------------------------------------- @node Project Status @chapter Project Status @quotation As soon as gfortran can parse all of the statements correctly, it will be in the ``larva'' state. When we generate code, the ``puppa'' state. When gfortran is done, we'll see if it will be a beautiful butterfly, or just a big bug.... --Andy Vaught, April 2000 @end quotation The start of the GNU Fortran 95 project was announced on the GCC homepage in March 18, 2000 (even though Andy had already been working on it for a while, of course). Gfortran is currently reaching the stage where is is able to compile real world programs. However it is still under development and has many rough edges. @menu * Compiler Status:: * Library Status:: * Proposed Extensions:: @end menu @node Compiler Status @section Compiler Status @table @emph @item Front end This is the part of gfortran which parses a source file, verifies that it is valid Fortran 95, performs compile time replacement of constants (PARAMETER variables) and reads and generate module files. This is almost complete. Every Fortran 95 source should be accepted, and most none-Fortran 95 source should be rejected. If you find a source file where this is not true, please tell us. You can use the -fsyntax-only switch to make gfortran quit after running the front end, effectively reducing it to a syntax checker. @item Middle end interface These are the parts of gfortran that take the parse tree generated by the front end and translate it to the GENERIC form required by the GCC back end. Work is ongoing in these parts of gfortran, but a large part has already been completed. @end table @node Library Status @section Library Status Some intrinsic functions map directly to library functions, and in most cases the name of the library function used depends on the type of the arguments. For some intrinsics we generate inline code, and for others, such as sin, cos and sqrt, we rely on the backend to use special instructions in the floating point unit of the CPU if available, or to fall back to a call to libm if these are not available. Implementation of some non-elemental intrinsic functions (eg. DOT_PRODUCT, AVERAGE) is not yet optimal. This is hard because we have to make decisions whether to use inline code (good for small arrays as no function call overhead occurs) or generate function calls (good for large arrays as it allows use of hand-optimized assembly routines, SIMD instructions, etc.) The IO library is in a mostly usable state. Unformatted I/O for @code{REAL(KIND=10)} variables is currently not recommended. Array intrinsics mostly work. @node Proposed Extensions @section Proposed Extensions Here's a list of proposed extensions for @command{gfortran}, in no particular order. Most of these are necessary to be fully compatible with existing Fortran compilers, but they are not part of the official J3 Fortran 95 standard. @subsection Compiler extensions: @itemize @bullet @item Flag for defining the kind number for default logicals. @item User-specified alignment rules for structures. @item Flag to generate @code{Makefile} info. @item Automatically extend single precision constants to double. @item Compile code that conserves memory by dynamically allocating common and module storage either on stack or heap. @item Flag to cause the compiler to distinguish between upper and lower case names. The Fortran 95 standard does not distinguish them. @item Compile flag to generate code for array conformance checking (suggest -CC). @item User control of symbol names (underscores, etc). @item Compile setting for maximum size of stack frame size before spilling parts to static or heap. @item Flag to force local variables into static space. @item Flag to force local variables onto stack. @item Flag to compile lines beginning with ``D''. @item Flag to ignore lines beginning with ``D''. @item Flag for maximum errors before ending compile. @item Generate code to check for null pointer dereferences -- prints locus of dereference instead of segfaulting. There was some discussion about this option in the g95 development mailing list. @item Allow setting the default unit number. @item Option to initialize otherwise uninitialized integer and floating point variables. @item Support for OpenMP directives. This also requires support from the runtime library and the rest of the compiler. @item Support for Fortran 200x. This includes several new features including floating point exceptions, extended use of allocatable arrays, C interoperability, Parameterizer data types and function pointers. @end itemize @subsection Environment Options @itemize @bullet @item Pluggable library modules for random numbers, linear algebra. LA should use BLAS calling conventions. @item Environment variables controlling actions on arithmetic exceptions like overflow, underflow, precision loss -- Generate NaN, abort, default. action. @item Set precision for fp units that support it (i387). @item Variable for setting fp rounding mode. @item Variable to fill uninitialized variables with a user-defined bit pattern. @item Environment variable controlling filename that is opened for that unit number. @item Environment variable to clear/trash memory being freed. @item Environment variable to control tracing of allocations and frees. @item Environment variable to display allocated memory at normal program end. @item Environment variable for filename for * IO-unit. @item Environment variable for temporary file directory. @item Environment variable forcing standard output to be line buffered (unix). @end itemize @node Runtime @chapter Runtime: Influencing runtime behavior with environment variables @cindex Runtime The behaviour of the @command{gfortran} can be influenced by environment variables. Malformed environment variables are silently ignored. @menu * GFORTRAN_STDIN_UNIT:: Unit number for standard input * GFORTRAN_STDOUT_UNIT:: Unit number for standard output * GFORTRAN_STDERR_UNIT:: Unit number for standard error * GFORTRAN_USE_STDERR:: Send library output to standard error * GFORTRAN_TMPDIR:: Directory for scratch files * GFORTRAN_UNBUFFERED_ALL:: Don't buffer output * GFORTRAN_SHOW_LOCUS:: Show location for runtime errors * GFORTRAN_OPTIONAL_PLUS:: Print leading + where permitted * GFORTRAN_DEFAULT_RECL:: Default record length for new files * GFORTRAN_LIST_SEPARATOR:: Separator for list output * GFORTRAN_CONVERT_UNIT:: Set endianness for unformatted I/O @end menu @node GFORTRAN_STDIN_UNIT @section GFORTRAN_STDIN_UNIT -- Unit number for standard input This environment variable can be used to select the unit number preconnected to standard input. This must be a positive integer. The default value is 5. @node GFORTRAN_STDOUT_UNIT @section GFORTRAN_STDOUT_UNIT -- Unit number for standard output This environment variable can be used to select the unit number preconnected to standard output. This must be a positive integer. The default value is 6. @node GFORTRAN_STDERR_UNIT @section GFORTRAN_STDERR_UNIT -- Unit number for standard error This environment variable can be used to select the unit number preconnected to standard error. This must be a positive integer. The default value is 0. @node GFORTRAN_USE_STDERR @section GFORTRAN_USE_STDERR:: Send library output to standard error This environment variable controls where library output is sent. If the first letter is 'y', 'Y' or '1', standard error is used. If the first letter is 'n', 'N' or '0', standard output is used. @node GFORTRAN_TMPDIR @section GFORTRAN_TMPDIR -- Directory for scratch files This environment variable controls where scratch files are created. Default is '/tmp'. @node GFORTRAN_UNBUFFERED_ALL @section GFORTRAN_UNBUFFERED_ALL -- Don't buffer output This environment variable controls wether all output is unbuffered. If the first letter is 'y', 'Y' or '1', all output is unbuffered. This will slow down large writes. If the first letter is 'n', 'N' or '0', output is bufferred. This is the default. @node GFORTRAN_SHOW_LOCUS @section GFORTRAN_SHOW_LOCUS -- Show location for runtime errors If the first letter is 'y', 'Y' or '1', filename and line numbers for runtime errors are printed. If the first letter is 'n', 'N' or '0', don't print filename and line numbers for runtime errors. The default is to print the location. @node GFORTRAN_OPTIONAL_PLUS @section GFORTRAN_OPTIONAL_PLUS -- Print leading + where permitted If the first letter is 'y', 'Y' or '1', a plus sign is printed where permitted by the Fortran standard. If the first lettter is 'n', 'N' or '0', a plus sign is not printed in most cases. Default is not to print plus signs. @node GFORTRAN_DEFAULT_RECL @section GFORTRAN_DEFAULT_RECL -- Default record lenght for new files This environment variable specifies the default record length for files which are opened without a @code{RECL} tag in the @code{OPEN} statement. This must be a positive integer. The default value is 1073741824. @node GFORTRAN_LIST_SEPARATOR @section GFORTRAN_LIST_SEPARATOR -- Separator for list output This environment variable specifies the separator when writing list-directed output. It may contain any number of spaces and at most one comma. If you specify this on the command line, be sure to quote spaces, as in @smallexample $ GFORTRAN_LIST_SEPARATOR=' , ' ./a.out @end smallexample when @code{a.out} is the gfortran program that you want to run. Default is a single space. @node GFORTRAN_CONVERT_UNIT @section GFORTRAN_CONVERT_UNIT -- Set endianness for unformatted I/O By setting the @code{GFORTRAN_CONVERT_UNIT variable}, it is possible to change the representation of data for unformatted files. The syntax for the @code{GFORTRAN_CONVERT_UNIT} variable is: @smallexample GFORTRAN_CONVERT_UNIT: mode | mode ';' exception ; mode: 'native' | 'swap' | 'big_endian' | 'little_endian' ; exception: mode ':' unit_list | unit_list ; unit_list: unit_spec | unit_list unit_spec ; unit_spec: INTEGER | INTEGER '-' INTEGER ; @end smallexample The variable consists of an optional default mode, followed by a list of optional exceptions, which are separated by semicolons from the preceding default and each other. Each exception consists of a format and a comma-separated list of units. Valid values for the modes are the same as for the @code{CONVERT} specifier: @itemize @w{} @item @code{NATIVE} Use the native format. This is the default. @item @code{SWAP} Swap between little- and big-endian. @item @code{LITTLE_ENDIAN} Use the little-endian format for unformatted files. @item @code{BIG_ENDIAN} Use the big-endian format for unformatted files. @end itemize A missing mode for an exception is taken to mean @code{BIG_ENDIAN}. Examples of values for @code{GFORTRAN_CONVERT_UNIT} are: @itemize @w{} @item @code{'big_endian'} Do all unformatted I/O in big_endian mode. @item @code{'little_endian;native:10-20,25'} Do all unformatted I/O in little_endian mode, except for units 10 to 20 and 25, which are in native format. @item @code{'10-20'} Units 10 to 20 are big-endian, the rest is native. @end itemize Setting the environment variables should be done on the command line or via the @code{export} command for @code{sh}-compatible shells and via @code{setenv} for @code{csh}-compatible shells. Example for @code{sh}: @smallexample $ gfortran foo.f90 $ GFORTRAN_CONVERT_UNIT='big_endian;native:10-20' ./a.out @end smallexample Example code for @code{csh}: @smallexample % gfortran foo.f90 % setenv GFORTRAN_CONVERT_UNIT 'big_endian;native:10-20' % ./a.out @end smallexample Using anything but the native representation for unformatted data carries a significant speed overhead. If speed in this area matters to you, it is best if you use this only for data that needs to be portable. @xref{CONVERT specifier}, for an alternative way to specify the data representation for unformatted files. @xref{Runtime Options}, for setting a default data representation for the whole program. The @code{CONVERT} specifier overrides the @code{-fconvert} compile options. @c --------------------------------------------------------------------- @c Extensions @c --------------------------------------------------------------------- @c Maybe this chapter should be merged with the 'Standards' section, @c whenever that is written :-) @node Extensions @chapter Extensions @cindex Extension @command{gfortran} implements a number of extensions over standard Fortran. This chapter contains information on their syntax and meaning. There are currently two categories of @command{gfortran} extensions, those that provide functionality beyond that provided by any standard, and those that are supported by @command{gfortran} purely for backward compatibility with legacy compilers. By default, @option{-std=gnu} allows the compiler to accept both types of extensions, but to warn about the use of the latter. Specifying either @option{-std=f95} or @option{-std=f2003} disables both types of extensions, and @option{-std=legacy} allows both without warning. @menu * Old-style kind specifications:: * Old-style variable initialization:: * Extensions to namelist:: * X format descriptor:: * Commas in FORMAT specifications:: * I/O item lists:: * Hexadecimal constants:: * Real array indices:: * Unary operators:: * Implicitly interconvert LOGICAL and INTEGER:: * Hollerith constants support:: * Cray pointers:: * CONVERT specifier:: @end menu @node Old-style kind specifications @section Old-style kind specifications @cindex Kind specifications @command{gfortran} allows old-style kind specifications in declarations. These look like: @smallexample TYPESPEC*k x,y,z @end smallexample where @code{TYPESPEC} is a basic type, and where @code{k} is a valid kind number for that type. The statement then declares @code{x}, @code{y} and @code{z} to be of type @code{TYPESPEC} with kind @code{k}. In other words, it is equivalent to the standard conforming declaration @smallexample TYPESPEC(k) x,y,z @end smallexample @node Old-style variable initialization @section Old-style variable initialization @cindex Initialization @command{gfortran} allows old-style initialization of variables of the form: @smallexample INTEGER*4 i/1/,j/2/ REAL*8 x(2,2) /3*0.,1./ @end smallexample These are only allowed in declarations without double colons (@code{::}), as these were introduced in Fortran 90 which also introduced a new syntax for variable initializations. The syntax for the individual initializers is as for the @code{DATA} statement, but unlike in a @code{DATA} statement, an initializer only applies to the variable immediately preceding. In other words, something like @code{INTEGER I,J/2,3/} is not valid. Examples of standard conforming code equivalent to the above example, are: @smallexample ! Fortran 90 INTEGER(4) :: i = 1, j = 2 REAL(8) :: x(2,2) = RESHAPE((/0.,0.,0.,1./),SHAPE(x)) ! Fortran 77 INTEGER i, j DOUBLE PRECISION x(2,2) DATA i,j,x /1,2,3*0.,1./ @end smallexample @node Extensions to namelist @section Extensions to namelist @cindex Namelist @command{gfortran} fully supports the Fortran 95 standard for namelist I/O including array qualifiers, substrings and fully qualified derived types. The output from a namelist write is compatible with namelist read. The output has all names in upper case and indentation to column 1 after the namelist name. Two extensions are permitted: Old-style use of $ instead of & @smallexample $MYNML X(:)%Y(2) = 1.0 2.0 3.0 CH(1:4) = "abcd" $END @end smallexample It should be noticed that the default terminator is / rather than &END. Querying of the namelist when inputting from stdin. After at least one space, entering ? sends to stdout the namelist name and the names of the variables in the namelist: @smallexample ? &mynml x x%y ch &end @end smallexample Entering =? outputs the namelist to stdout, as if WRITE (*,NML = mynml) had been called: @smallexample =? &MYNML X(1)%Y= 0.000000 , 1.000000 , 0.000000 , X(2)%Y= 0.000000 , 2.000000 , 0.000000 , X(3)%Y= 0.000000 , 3.000000 , 0.000000 , CH=abcd, / @end smallexample To aid this dialog, when input is from stdin, errors send their messages to stderr and execution continues, even if IOSTAT is set. PRINT namelist is permitted. This causes an error if -std=f95 is used. @smallexample PROGRAM test_print REAL, dimension (4) :: x = (/1.0, 2.0, 3.0, 4.0/) NAMELIST /mynml/ x PRINT mynml END PROGRAM test_print @end smallexample @node X format descriptor @section X format descriptor @cindex X format descriptor To support legacy codes, @command{gfortran} permits the count field of the X edit descriptor in FORMAT statements to be omitted. When omitted, the count is implicitly assumed to be one. @smallexample PRINT 10, 2, 3 10 FORMAT (I1, X, I1) @end smallexample @node Commas in FORMAT specifications @section Commas in FORMAT specifications @cindex Commas in FORMAT specifications To support legacy codes, @command{gfortran} allows the comma separator to be omitted immediately before and after character string edit descriptors in FORMAT statements. @smallexample PRINT 10, 2, 3 10 FORMAT ('FOO='I1' BAR='I2) @end smallexample @node I/O item lists @section I/O item lists @cindex I/O item lists To support legacy codes, @command{gfortran} allows the input item list of the READ statement, and the output item lists of the WRITE and PRINT statements to start with a comma. @node Hexadecimal constants @section Hexadecimal constants @cindex Hexadecimal constants As a GNU extension, @command{gfortran} allows hexadecimal constants to be specified using the X prefix, in addition to the standard Z prefix. @node Real array indices @section Real array indices @cindex Real array indices As a GNU extension, @command{gfortran} allows arrays to be indexed using real types, whose values are implicitly converted to integers. @node Unary operators @section Unary operators @cindex Unary operators As a GNU extension, @command{gfortran} allows unary plus and unary minus operators to appear as the second operand of binary arithmetic operators without the need for parenthesis. @smallexample X = Y * -Z @end smallexample @node Implicitly interconvert LOGICAL and INTEGER @section Implicitly interconvert LOGICAL and INTEGER @cindex Implicitly interconvert LOGICAL and INTEGER As a GNU extension for backwards compatibility with other compilers, @command{gfortran} allows the implicit conversion of LOGICALs to INTEGERs and vice versa. When converting from a LOGICAL to an INTEGER, the numeric value of @code{.FALSE.} is zero, and that of @code{.TRUE.} is one. When converting from INTEGER to LOGICAL, the value zero is interpreted as @code{.FALSE.} and any nonzero value is interpreted as @code{.TRUE.}. @smallexample INTEGER*4 i i = .FALSE. @end smallexample @node Hollerith constants support @section Hollerith constants support @cindex Hollerith constants A Hollerith constant is a string of characters preceded by the letter @samp{H} or @samp{h}, and there must be an literal, unsigned, nonzero default integer constant indicating the number of characters in the string. Hollerith constants are stored as byte strings, one character per byte. @command{gfortran} supports Hollerith constants. They can be used as the right hands in the @code{DATA} statement and @code{ASSIGN} statement, also as the arguments. The left hands can be of Integer, Real, Complex and Logical type. The constant will be padded or truncated to fit the size of left hand. Valid Hollerith constants examples: @smallexample complex*16 x(2) data x /16Habcdefghijklmnop, 16Hqrstuvwxyz012345/ call foo (4H abc) x(1) = 16Habcdefghijklmnop @end smallexample Invalid Hollerith constants examples: @smallexample integer*4 a a = 8H12345678 ! The Hollerith constant is too long. It will be truncated. a = 0H ! At least one character needed. @end smallexample @node Cray pointers @section Cray pointers @cindex Cray pointers Cray pointers are part of a non-standard extension that provides a C-like pointer in Fortran. This is accomplished through a pair of variables: an integer "pointer" that holds a memory address, and a "pointee" that is used to dereference the pointer. Pointer/pointee pairs are declared in statements of the form: @smallexample pointer ( , ) @end smallexample or, @smallexample pointer ( , ), ( , ), ... @end smallexample The pointer is an integer that is intended to hold a memory address. The pointee may be an array or scalar. A pointee can be an assumed size array -- that is, the last dimension may be left unspecified by using a '*' in place of a value -- but a pointee cannot be an assumed shape array. No space is allocated for the pointee. The pointee may have its type declared before or after the pointer statement, and its array specification (if any) may be declared before, during, or after the pointer statement. The pointer may be declared as an integer prior to the pointer statement. However, some machines have default integer sizes that are different than the size of a pointer, and so the following code is not portable: @smallexample integer ipt pointer (ipt, iarr) @end smallexample If a pointer is declared with a kind that is too small, the compiler will issue a warning; the resulting binary will probably not work correctly, because the memory addresses stored in the pointers may be truncated. It is safer to omit the first line of the above example; if explicit declaration of ipt's type is omitted, then the compiler will ensure that ipt is an integer variable large enough to hold a pointer. Pointer arithmetic is valid with Cray pointers, but it is not the same as C pointer arithmetic. Cray pointers are just ordinary integers, so the user is responsible for determining how many bytes to add to a pointer in order to increment it. Consider the following example: @smallexample real target(10) real pointee(10) pointer (ipt, pointee) ipt = loc (target) ipt = ipt + 1 @end smallexample The last statement does not set ipt to the address of @code{target(1)}, as one familiar with C pointer arithmetic might expect. Adding 1 to ipt just adds one byte to the address stored in ipt. Any expression involving the pointee will be translated to use the value stored in the pointer as the base address. To get the address of elements, this extension provides an intrinsic function loc(), loc() is essentially the C '&' operator, except the address is cast to an integer type: @smallexample real ar(10) pointer(ipt, arpte(10)) real arpte ipt = loc(ar) ! Makes arpte is an alias for ar arpte(1) = 1.0 ! Sets ar(1) to 1.0 @end smallexample The pointer can also be set by a call to a malloc-type function. There is no malloc intrinsic implemented as part of the Cray pointer extension, but it might be a useful future addition to @command{gfortran}. Even without an intrinsic malloc function, dynamic memory allocation can be combined with Cray pointers by calling a short C function: @smallexample mymalloc.c: void mymalloc_(void **ptr, int *nbytes) @{ *ptr = malloc(*nbytes); return; @} caller.f: program caller integer ipinfo; real*4 data pointer (ipdata, data(1024)) call mymalloc(ipdata,4*1024) end @end smallexample Cray pointees often are used to alias an existing variable. For example: @smallexample integer target(10) integer iarr(10) pointer (ipt, iarr) ipt = loc(target) @end smallexample As long as ipt remains unchanged, iarr is now an alias for target. The optimizer, however, will not detect this aliasing, so it is unsafe to use iarr and target simultaneously. Using a pointee in any way that violates the Fortran aliasing rules or assumptions is illegal. It is the user's responsibility to avoid doing this; the compiler works under the assumption that no such aliasing occurs. Cray pointers will work correctly when there is no aliasing (i.e., when they're used to access a dynamically allocated block of memory), and also in any routine where a pointee is used, but any variable with which it shares storage is not used. Code that violates these rules may not run as the user intends. This is not a bug in the optimizer; any code that violates the aliasing rules is illegal. (Note that this is not unique to gfortran; any Fortran compiler that supports Cray pointers will ``incorrectly'' optimize code with illegal aliasing.) There are a number of restrictions on the attributes that can be applied to Cray pointers and pointees. Pointees may not have the attributes ALLOCATABLE, INTENT, OPTIONAL, DUMMY, TARGET, EXTERNAL, INTRINSIC, or POINTER. Pointers may not have the attributes DIMENSION, POINTER, TARGET, ALLOCATABLE, EXTERNAL, or INTRINSIC. Pointees may not occur in more than one pointer statement. A pointee cannot be a pointer. Pointees cannot occur in equivalence, common, or data statements. A pointer may be modified during the course of a program, and this will change the location to which the pointee refers. However, when pointees are passed as arguments, they are treated as ordinary variables in the invoked function. Subsequent changes to the pointer will not change the base address of the array that was passed. @node CONVERT specifier @section CONVERT specifier @cindex CONVERT specifier gfortran allows the conversion of unformatted data between little- and big-endian representation to facilitate moving of data between different systems. The conversion can be indicated with the @code{CONVERT} specifier on the @code{OPEN} statement. @xref{GFORTRAN_CONVERT_UNIT}, for an alternative way of specifying the data format via an environment variable. Valid values for @code{CONVERT} are: @itemize @w{} @item @code{CONVERT='NATIVE'} Use the native format. This is the default. @item @code{CONVERT='SWAP'} Swap between little- and big-endian. @item @code{CONVERT='LITTLE_ENDIAN'} Use the little-endian representation for unformatted files. @item @code{CONVERT='BIG_ENDIAN'} Use the big-endian representation for unformatted files. @end itemize Using the option could look like this: @smallexample open(file='big.dat',form='unformatted',access='sequential', & convert='big_endian') @end smallexample The value of the conversion can be queried by using @code{INQUIRE(CONVERT=ch)}. The values returned are @code{'BIG_ENDIAN'} and @code{'LITTLE_ENDIAN'}. @code{CONVERT} works between big- and little-endian for @code{INTEGER} values of all supported kinds and for @code{REAL} on IEEE sytems of kinds 4 and 8. Conversion between different ``extended double'' types on different architectures such as m68k and x86_64, which gfortran supports as @code{REAL(KIND=10)} will probably not work. @emph{Note that the values specified via the GFORTRAN_CONVERT_UNIT environment variable will override the CONVERT specifier in the open statement}. This is to give control over data formats to a user who does not have the source code of his program available. Using anything but the native representation for unformatted data carries a significant speed overhead. If speed in this area matters to you, it is best if you use this only for data that needs to be portable. @c --------------------------------------------------------------------- @include intrinsic.texi @c --------------------------------------------------------------------- @c --------------------------------------------------------------------- @c Contributing @c --------------------------------------------------------------------- @node Contributing @chapter Contributing @cindex Contributing Free software is only possible if people contribute to efforts to create it. We're always in need of more people helping out with ideas and comments, writing documentation and contributing code. If you want to contribute to GNU Fortran 95, have a look at the long lists of projects you can take on. Some of these projects are small, some of them are large; some are completely orthogonal to the rest of what is happening on @command{gfortran}, but others are ``mainstream'' projects in need of enthusiastic hackers. All of these projects are important! We'll eventually get around to the things here, but they are also things doable by someone who is willing and able. @menu * Contributors:: * Projects:: @end menu @node Contributors @section Contributors to GNU Fortran 95 @cindex Contributors @cindex Credits @cindex Authors Most of the parser was hand-crafted by @emph{Andy Vaught}, who is also the initiator of the whole project. Thanks Andy! Most of the interface with GCC was written by @emph{Paul Brook}. The following individuals have contributed code and/or ideas and significant help to the gfortran project (in no particular order): @itemize @minus @item Andy Vaught @item Katherine Holcomb @item Tobias Schlüter @item Steven Bosscher @item Toon Moene @item Tim Prince @item Niels Kristian Bech Jensen @item Steven Johnson @item Paul Brook @item Feng Wang @item Bud Davis @item Paul Thomas @item François-Xavier Coudert @item Steve Kargl @item Jerry Delisle @item Janne Blomqvist @item Erik Edelmann @item Thomas Koenig @item Asher Langton @end itemize The following people have contributed bug reports, smaller or larger patches, and much needed feedback and encouragement for the @command{gfortran} project: @itemize @minus @item Erik Schnetter @item Bill Clodius @item Kate Hedstrom @end itemize Many other individuals have helped debug, test and improve @command{gfortran} over the past few years, and we welcome you to do the same! If you already have done so, and you would like to see your name listed in the list above, please contact us. @node Projects @section Projects @table @emph @item Help build the test suite Solicit more code for donation to the test suite. We can keep code private on request. @item Bug hunting/squishing Find bugs and write more test cases! Test cases are especially very welcome, because it allows us to concentrate on fixing bugs instead of isolating them. @item Smaller projects (``bug'' fixes): @itemize @minus @item Allow init exprs to be numbers raised to integer powers. @item Implement correct rounding. @item Implement F restrictions on Fortran 95 syntax. @item See about making Emacs-parsable error messages. @end itemize @end table If you wish to work on the runtime libraries, please contact a project maintainer. @c TODO: email! @c --------------------------------------------------------------------- @c Standards @c --------------------------------------------------------------------- @node Standards @chapter Standards @cindex Standards The GNU Fortran 95 Compiler aims to be a conforming implementation of ISO/IEC 1539:1997 (Fortran 95). In the future it may also support other variants of and extensions to the Fortran language. These include ANSI Fortran 77, ISO Fortran 90, ISO Fortran 2003 and OpenMP. @menu * Fortran 2003 status:: @end menu @node Fortran 2003 status @section Fortran 2003 status Although @command{gfortran} focuses on implementing the Fortran 95 standard for the time being, a few Fortran 2003 features are currently available. @itemize @item Intrinsics @code{command_argument_count}, @code{get_command}, @code{get_command_argument}, and @code{get_environment_variable}. @item @cindex Array constructors @cindex @code{[...]} Array constructors using square brackets. That is, @code{[...]} rather than @code{(/.../)}. @item @cindex @code{FLUSH} statement @code{FLUSH} statement. @item @cindex @code{IOMSG=} specifier @code{IOMSG=} specifier for I/O statements. @item @cindex @code{ENUM} statement @cindex @code{ENUMERATOR} statement @cindex @command{-fshort-enums} Support for the declaration of enumeration constants via the @code{ENUM} and @code{ENUMERATOR} statements. Interoperability with @command{gcc} is guaranteed also for the case where the @command{-fshort-enums} command line option is given. @end itemize @c --------------------------------------------------------------------- @c GNU General Public License @c --------------------------------------------------------------------- @include gpl.texi @c --------------------------------------------------------------------- @c GNU Free Documentation License @c --------------------------------------------------------------------- @include fdl.texi @c --------------------------------------------------------------------- @c Funding Free Software @c --------------------------------------------------------------------- @include funding.texi @c --------------------------------------------------------------------- @c Index @c --------------------------------------------------------------------- @node Index @unnumbered Index @printindex cp @bye