\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 59 Temple Place - Suite 330 Boston, MA 02111-1307 USA @insertcopying @end ifinfo Contributed by Steven Bosscher (@email{s.bosscher@@gcc.gnu.org}). @setchapternewpage odd @titlepage @title Using GNU Fortran 95 @sp 2 @center Steven Bosscher @page @vskip 0pt plus 1filll For the @value{version-GCC} Version* @sp 1 Published by the Free Software Foundation @* 59 Temple Place - Suite 330@* Boston, MA 02111-1307, 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, Copying,, (DIR) @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 * 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. * 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} * Extensions:: Language extensions implemented by @command{gfortran} * Intrinsic Procedures:: Intrinsic procedures supported by @command{gfortran} * Index:: Index of this documentation. @end menu @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 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 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 compiler 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 contains 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 with 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 a pass to generate a representation of the semantics of the program in the source code in the GCC language independent intermediate language, 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, pass the optimized AST and generate assembly for 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: 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, or 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 still under development. The following features should be usable for real programs: @itemize @minus @item List directed @item Unformatted sequential @end itemize Usable with bugs: @itemize @minus @item Formatted sequential ('T' edit descriptor, and others) @end itemize Not recommended: @itemize @minus @item Unformatted direct access @item Formatted direct access @end itemize Many Fortran programs only use a small subset of the available IO capabilities, so your mileage may vary. @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 a @code{Makefile} info. @item Automatically extend single precision constants to double. @item Cray pointers (this was high on the @command{g77} wishlist). @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 switch for changing the interpretation of a backslash from a character to ``C''-style escape characters. @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 default unit number. @item Option to initialize of 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 Variables 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). @item Variable for swapping endianness during unformatted read. @item Variable for swapping Endianness during unformatted write. @end itemize @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:: @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 fortran95 standard for namelist io 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 produce send their messages to stderr and execution continues, even if IOSTAT is set. @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 @include intrinsic.texi @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 @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 two 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 and extensions to the Fortran language. This includes ANSI Fortran 77, Fortran 90, Fortran 2000 (not yet finalized), and OpenMP. @node Index @unnumbered Index @printindex cp @bye