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| author | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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| committer | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
| commit | abdaadbcae30fe0c9a66c7516798279fdfd97750 (patch) | |
| tree | 00a54a6e25601e43876d03c1a4a12a749d4a914c /share/doc/gfortran/Interoperable-Subroutines-and-Functions.html | |
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diff --git a/share/doc/gfortran/Interoperable-Subroutines-and-Functions.html b/share/doc/gfortran/Interoperable-Subroutines-and-Functions.html new file mode 100644 index 0000000..efedb88 --- /dev/null +++ b/share/doc/gfortran/Interoperable-Subroutines-and-Functions.html @@ -0,0 +1,189 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1999-2023 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 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>The GNU Fortran Compiler: Interoperable Subroutines and Functions</title> + +<meta name="description" content="The GNU Fortran Compiler: Interoperable Subroutines and Functions"> +<meta name="keywords" content="The GNU Fortran Compiler: Interoperable Subroutines and Functions"> +<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="Interoperability-with-C.html#Interoperability-with-C" rel="up" title="Interoperability with C"> +<link href="Working-with-C-Pointers.html#Working-with-C-Pointers" rel="next" title="Working with C Pointers"> +<link href="Interoperable-Global-Variables.html#Interoperable-Global-Variables" rel="previous" title="Interoperable Global Variables"> +<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="Interoperable-Subroutines-and-Functions"></a> +<div class="header"> +<p> +Next: <a href="Working-with-C-Pointers.html#Working-with-C-Pointers" accesskey="n" rel="next">Working with C Pointers</a>, Previous: <a href="Interoperable-Global-Variables.html#Interoperable-Global-Variables" accesskey="p" rel="previous">Interoperable Global Variables</a>, Up: <a href="Interoperability-with-C.html#Interoperability-with-C" accesskey="u" rel="up">Interoperability with C</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="Interoperable-Subroutines-and-Functions-1"></a> +<h4 class="subsection">6.1.4 Interoperable Subroutines and Functions</h4> +<a name="index-C-procedure-interoperability"></a> +<a name="index-procedure-interoperability-with-C"></a> +<a name="index-function-interoperability-with-C"></a> +<a name="index-subroutine-interoperability-with-C"></a> +<a name="index-interoperability_002c-subroutine-and-function"></a> + +<p>Subroutines and functions have to have the <code>BIND(C)</code> attribute to +be compatible with C. The dummy argument declaration is relatively +straightforward. However, one needs to be careful because C uses +call-by-value by default while Fortran behaves usually similar to +call-by-reference. Furthermore, strings and pointers are handled +differently. +</p> +<p>To pass a variable by value, use the <code>VALUE</code> attribute. +Thus, the following C prototype +</p> +<div class="smallexample"> +<pre class="smallexample"><code>int func(int i, int *j)</code> +</pre></div> + +<p>matches the Fortran declaration +</p> +<div class="smallexample"> +<pre class="smallexample"> integer(c_int) function func(i,j) + use iso_c_binding, only: c_int + integer(c_int), VALUE :: i + integer(c_int) :: j +</pre></div> + +<p>Note that pointer arguments also frequently need the <code>VALUE</code> attribute, +see <a href="Working-with-C-Pointers.html#Working-with-C-Pointers">Working with C Pointers</a>. +</p> +<p>Strings are handled quite differently in C and Fortran. In C a string +is a <code>NUL</code>-terminated array of characters while in Fortran each string +has a length associated with it and is thus not terminated (by e.g. +<code>NUL</code>). For example, if you want to use the following C function, +</p> +<div class="smallexample"> +<pre class="smallexample"> #include <stdio.h> + void print_C(char *string) /* equivalent: char string[] */ + { + printf("%s\n", string); + } +</pre></div> + +<p>to print “Hello World” from Fortran, you can call it using +</p> +<div class="smallexample"> +<pre class="smallexample"> use iso_c_binding, only: C_CHAR, C_NULL_CHAR + interface + subroutine print_c(string) bind(C, name="print_C") + use iso_c_binding, only: c_char + character(kind=c_char) :: string(*) + end subroutine print_c + end interface + call print_c(C_CHAR_"Hello World"//C_NULL_CHAR) +</pre></div> + +<p>As the example shows, you need to ensure that the +string is <code>NUL</code> terminated. Additionally, the dummy argument +<var>string</var> of <code>print_C</code> is a length-one assumed-size +array; using <code>character(len=*)</code> is not allowed. The example +above uses <code>c_char_"Hello World"</code> to ensure the string +literal has the right type; typically the default character +kind and <code>c_char</code> are the same and thus <code>"Hello World"</code> +is equivalent. However, the standard does not guarantee this. +</p> +<p>The use of strings is now further illustrated using the C library +function <code>strncpy</code>, whose prototype is +</p> +<div class="smallexample"> +<pre class="smallexample"> char *strncpy(char *restrict s1, const char *restrict s2, size_t n); +</pre></div> + +<p>The function <code>strncpy</code> copies at most <var>n</var> characters from +string <var>s2</var> to <var>s1</var> and returns <var>s1</var>. In the following +example, we ignore the return value: +</p> +<div class="smallexample"> +<pre class="smallexample"> use iso_c_binding + implicit none + character(len=30) :: str,str2 + interface + ! Ignore the return value of strncpy -> subroutine + ! "restrict" is always assumed if we do not pass a pointer + subroutine strncpy(dest, src, n) bind(C) + import + character(kind=c_char), intent(out) :: dest(*) + character(kind=c_char), intent(in) :: src(*) + integer(c_size_t), value, intent(in) :: n + end subroutine strncpy + end interface + str = repeat('X',30) ! Initialize whole string with 'X' + call strncpy(str, c_char_"Hello World"//C_NULL_CHAR, & + len(c_char_"Hello World",kind=c_size_t)) + print '(a)', str ! prints: "Hello WorldXXXXXXXXXXXXXXXXXXX" + end +</pre></div> + +<p>The intrinsic procedures are described in <a href="Intrinsic-Procedures.html#Intrinsic-Procedures">Intrinsic Procedures</a>. +</p> +<hr> +<div class="header"> +<p> +Next: <a href="Working-with-C-Pointers.html#Working-with-C-Pointers" accesskey="n" rel="next">Working with C Pointers</a>, Previous: <a href="Interoperable-Global-Variables.html#Interoperable-Global-Variables" accesskey="p" rel="previous">Interoperable Global Variables</a>, Up: <a href="Interoperability-with-C.html#Interoperability-with-C" accesskey="u" rel="up">Interoperability with C</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> |