177 lines
8.8 KiB
HTML
177 lines
8.8 KiB
HTML
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
||
|
|
<html>
|
||
|
|
<!-- Copyright (C) 1999-2016 Free Software Foundation, Inc.
|
||
|
|
|
||
|
|
Permission is granted to copy, distribute and/or modify this document
|
||
|
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
||
|
|
any later version published by the Free Software Foundation; with the
|
||
|
|
Invariant Sections being "Funding Free Software", the Front-Cover
|
||
|
|
Texts being (a) (see below), and with the Back-Cover Texts being (b)
|
||
|
|
(see below). A copy of the license is included in the 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. -->
|
||
|
|
<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
|
||
|
|
<head>
|
||
|
|
<title>The GNU Fortran Compiler: Argument passing conventions</title>
|
||
|
|
|
||
|
|
<meta name="description" content="The GNU Fortran Compiler: Argument passing conventions">
|
||
|
|
<meta name="keywords" content="The GNU Fortran Compiler: Argument passing conventions">
|
||
|
|
<meta name="resource-type" content="document">
|
||
|
|
<meta name="distribution" content="global">
|
||
|
|
<meta name="Generator" content="makeinfo">
|
||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
||
|
|
<link href="index.html#Top" rel="start" title="Top">
|
||
|
|
<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
|
||
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
||
|
|
<link href="Naming-and-argument_002dpassing-conventions.html#Naming-and-argument_002dpassing-conventions" rel="up" title="Naming and argument-passing conventions">
|
||
|
|
<link href="Coarray-Programming.html#Coarray-Programming" rel="next" title="Coarray Programming">
|
||
|
|
<link href="Naming-conventions.html#Naming-conventions" rel="prev" title="Naming conventions">
|
||
|
|
<style type="text/css">
|
||
|
|
<!--
|
||
|
|
a.summary-letter {text-decoration: none}
|
||
|
|
blockquote.smallquotation {font-size: smaller}
|
||
|
|
div.display {margin-left: 3.2em}
|
||
|
|
div.example {margin-left: 3.2em}
|
||
|
|
div.indentedblock {margin-left: 3.2em}
|
||
|
|
div.lisp {margin-left: 3.2em}
|
||
|
|
div.smalldisplay {margin-left: 3.2em}
|
||
|
|
div.smallexample {margin-left: 3.2em}
|
||
|
|
div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
|
||
|
|
div.smalllisp {margin-left: 3.2em}
|
||
|
|
kbd {font-style:oblique}
|
||
|
|
pre.display {font-family: inherit}
|
||
|
|
pre.format {font-family: inherit}
|
||
|
|
pre.menu-comment {font-family: serif}
|
||
|
|
pre.menu-preformatted {font-family: serif}
|
||
|
|
pre.smalldisplay {font-family: inherit; font-size: smaller}
|
||
|
|
pre.smallexample {font-size: smaller}
|
||
|
|
pre.smallformat {font-family: inherit; font-size: smaller}
|
||
|
|
pre.smalllisp {font-size: smaller}
|
||
|
|
span.nocodebreak {white-space:nowrap}
|
||
|
|
span.nolinebreak {white-space:nowrap}
|
||
|
|
span.roman {font-family:serif; font-weight:normal}
|
||
|
|
span.sansserif {font-family:sans-serif; font-weight:normal}
|
||
|
|
ul.no-bullet {list-style: none}
|
||
|
|
-->
|
||
|
|
</style>
|
||
|
|
|
||
|
|
|
||
|
|
</head>
|
||
|
|
|
||
|
|
<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
|
||
|
|
<a name="Argument-passing-conventions"></a>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Previous: <a href="Naming-conventions.html#Naming-conventions" accesskey="p" rel="prev">Naming conventions</a>, Up: <a href="Naming-and-argument_002dpassing-conventions.html#Naming-and-argument_002dpassing-conventions" accesskey="u" rel="up">Naming and argument-passing conventions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
|
||
|
|
</div>
|
||
|
|
<hr>
|
||
|
|
<a name="Argument-passing-conventions-1"></a>
|
||
|
|
<h4 class="subsection">7.4.2 Argument passing conventions</h4>
|
||
|
|
|
||
|
|
<p>Subroutines do not return a value (matching C99’s <code>void</code>) while
|
||
|
|
functions either return a value as specified in the platform ABI or
|
||
|
|
the result variable is passed as hidden argument to the function and
|
||
|
|
no result is returned. A hidden result variable is used when the
|
||
|
|
result variable is an array or of type <code>CHARACTER</code>.
|
||
|
|
</p>
|
||
|
|
<p>Arguments are passed according to the platform ABI. In particular,
|
||
|
|
complex arguments might not be compatible to a struct with two real
|
||
|
|
components for the real and imaginary part. The argument passing
|
||
|
|
matches the one of C99’s <code>_Complex</code>. Functions with scalar
|
||
|
|
complex result variables return their value and do not use a
|
||
|
|
by-reference argument. Note that with the <samp>-ff2c</samp> option,
|
||
|
|
the argument passing is modified and no longer completely matches
|
||
|
|
the platform ABI. Some other Fortran compilers use <code>f2c</code>
|
||
|
|
semantic by default; this might cause problems with
|
||
|
|
interoperablility.
|
||
|
|
</p>
|
||
|
|
<p>GNU Fortran passes most arguments by reference, i.e. by passing a
|
||
|
|
pointer to the data. Note that the compiler might use a temporary
|
||
|
|
variable into which the actual argument has been copied, if required
|
||
|
|
semantically (copy-in/copy-out).
|
||
|
|
</p>
|
||
|
|
<p>For arguments with <code>ALLOCATABLE</code> and <code>POINTER</code>
|
||
|
|
attribute (including procedure pointers), a pointer to the pointer
|
||
|
|
is passed such that the pointer address can be modified in the
|
||
|
|
procedure.
|
||
|
|
</p>
|
||
|
|
<p>For dummy arguments with the <code>VALUE</code> attribute: Scalar arguments
|
||
|
|
of the type <code>INTEGER</code>, <code>LOGICAL</code>, <code>REAL</code> and
|
||
|
|
<code>COMPLEX</code> are passed by value according to the platform ABI.
|
||
|
|
(As vendor extension and not recommended, using <code>%VAL()</code> in the
|
||
|
|
call to a procedure has the same effect.) For <code>TYPE(C_PTR)</code> and
|
||
|
|
procedure pointers, the pointer itself is passed such that it can be
|
||
|
|
modified without affecting the caller.
|
||
|
|
</p>
|
||
|
|
<p>For Boolean (<code>LOGICAL</code>) arguments, please note that GCC expects
|
||
|
|
only the integer value 0 and 1. If a GNU Fortran <code>LOGICAL</code>
|
||
|
|
variable contains another integer value, the result is undefined.
|
||
|
|
As some other Fortran compilers use <em>-1</em> for <code>.TRUE.</code>,
|
||
|
|
extra care has to be taken – such as passing the value as
|
||
|
|
<code>INTEGER</code>. (The same value restriction also applies to other
|
||
|
|
front ends of GCC, e.g. to GCC’s C99 compiler for <code>_Bool</code>
|
||
|
|
or GCC’s Ada compiler for <code>Boolean</code>.)
|
||
|
|
</p>
|
||
|
|
<p>For arguments of <code>CHARACTER</code> type, the character length is passed
|
||
|
|
as hidden argument. For deferred-length strings, the value is passed
|
||
|
|
by reference, otherwise by value. The character length has the type
|
||
|
|
<code>INTEGER(kind=4)</code>. Note with C binding, <code>CHARACTER(len=1)</code>
|
||
|
|
result variables are returned according to the platform ABI and no
|
||
|
|
hidden length argument is used for dummy arguments; with <code>VALUE</code>,
|
||
|
|
those variables are passed by value.
|
||
|
|
</p>
|
||
|
|
<p>For <code>OPTIONAL</code> dummy arguments, an absent argument is denoted
|
||
|
|
by a NULL pointer, except for scalar dummy arguments of type
|
||
|
|
<code>INTEGER</code>, <code>LOGICAL</code>, <code>REAL</code> and <code>COMPLEX</code>
|
||
|
|
which have the <code>VALUE</code> attribute. For those, a hidden Boolean
|
||
|
|
argument (<code>logical(kind=C_bool),value</code>) is used to indicate
|
||
|
|
whether the argument is present.
|
||
|
|
</p>
|
||
|
|
<p>Arguments which are assumed-shape, assumed-rank or deferred-rank
|
||
|
|
arrays or, with <samp>-fcoarray=lib</samp>, allocatable scalar coarrays use
|
||
|
|
an array descriptor. All other arrays pass the address of the
|
||
|
|
first element of the array. With <samp>-fcoarray=lib</samp>, the token
|
||
|
|
and the offset belonging to nonallocatable coarrays dummy arguments
|
||
|
|
are passed as hidden argument along the character length hidden
|
||
|
|
arguments. The token is an oparque pointer identifying the coarray
|
||
|
|
and the offset is a passed-by-value integer of kind <code>C_PTRDIFF_T</code>,
|
||
|
|
denoting the byte offset between the base address of the coarray and
|
||
|
|
the passed scalar or first element of the passed array.
|
||
|
|
</p>
|
||
|
|
<p>The arguments are passed in the following order
|
||
|
|
</p><ul>
|
||
|
|
<li> Result variable, when the function result is passed by reference
|
||
|
|
</li><li> Character length of the function result, if it is a of type
|
||
|
|
<code>CHARACTER</code> and no C binding is used
|
||
|
|
</li><li> The arguments in the order in which they appear in the Fortran
|
||
|
|
declaration
|
||
|
|
</li><li> The the present status for optional arguments with value attribute,
|
||
|
|
which are internally passed by value
|
||
|
|
</li><li> The character length and/or coarray token and offset for the first
|
||
|
|
argument which is a <code>CHARACTER</code> or a nonallocatable coarray dummy
|
||
|
|
argument, followed by the hidden arguments of the next dummy argument
|
||
|
|
of such a type
|
||
|
|
</li></ul>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
<hr>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Previous: <a href="Naming-conventions.html#Naming-conventions" accesskey="p" rel="prev">Naming conventions</a>, Up: <a href="Naming-and-argument_002dpassing-conventions.html#Naming-and-argument_002dpassing-conventions" accesskey="u" rel="up">Naming and argument-passing conventions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
</body>
|
||
|
|
</html>
|