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diff --git a/share/doc/gfortran/STRUCTURE-and-RECORD.html b/share/doc/gfortran/STRUCTURE-and-RECORD.html new file mode 100644 index 0000000..59640da --- /dev/null +++ b/share/doc/gfortran/STRUCTURE-and-RECORD.html @@ -0,0 +1,239 @@ +<!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: STRUCTURE and RECORD</title> + +<meta name="description" content="The GNU Fortran Compiler: STRUCTURE and RECORD"> +<meta name="keywords" content="The GNU Fortran Compiler: STRUCTURE and RECORD"> +<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="Extensions-implemented-in-GNU-Fortran.html#Extensions-implemented-in-GNU-Fortran" rel="up" title="Extensions implemented in GNU Fortran"> +<link href="UNION-and-MAP.html#UNION-and-MAP" rel="next" title="UNION and MAP"> +<link href="Read_002fWrite-after-EOF-marker.html#Read_002fWrite-after-EOF-marker" rel="previous" title="Read/Write after EOF marker"> +<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="STRUCTURE-and-RECORD"></a> +<div class="header"> +<p> +Next: <a href="UNION-and-MAP.html#UNION-and-MAP" accesskey="n" rel="next">UNION and MAP</a>, Previous: <a href="Read_002fWrite-after-EOF-marker.html#Read_002fWrite-after-EOF-marker" accesskey="p" rel="previous">Read/Write after EOF marker</a>, Up: <a href="Extensions-implemented-in-GNU-Fortran.html#Extensions-implemented-in-GNU-Fortran" accesskey="u" rel="up">Extensions implemented in GNU Fortran</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="STRUCTURE-and-RECORD-1"></a> +<h4 class="subsection">5.1.22 <code>STRUCTURE</code> and <code>RECORD</code></h4> +<a name="index-STRUCTURE"></a> +<a name="index-RECORD"></a> + +<p>Record structures are a pre-Fortran-90 vendor extension to create +user-defined aggregate data types. Support for record structures in GNU +Fortran can be enabled with the <samp>-fdec-structure</samp> compile flag. +If you have a choice, you should instead use Fortran 90’s “derived types”, +which have a different syntax. +</p> +<p>In many cases, record structures can easily be converted to derived types. +To convert, replace <code>STRUCTURE /</code><var>structure-name</var><code>/</code> +by <code>TYPE</code> <var>type-name</var>. Additionally, replace +<code>RECORD /</code><var>structure-name</var><code>/</code> by +<code>TYPE(</code><var>type-name</var><code>)</code>. Finally, in the component access, +replace the period (<code>.</code>) by the percent sign (<code>%</code>). +</p> +<p>Here is an example of code using the non portable record structure syntax: +</p> +<div class="example"> +<pre class="example">! Declaring a structure named ``item'' and containing three fields: +! an integer ID, an description string and a floating-point price. +STRUCTURE /item/ + INTEGER id + CHARACTER(LEN=200) description + REAL price +END STRUCTURE + +! Define two variables, an single record of type ``item'' +! named ``pear'', and an array of items named ``store_catalog'' +RECORD /item/ pear, store_catalog(100) + +! We can directly access the fields of both variables +pear.id = 92316 +pear.description = "juicy D'Anjou pear" +pear.price = 0.15 +store_catalog(7).id = 7831 +store_catalog(7).description = "milk bottle" +store_catalog(7).price = 1.2 + +! We can also manipulate the whole structure +store_catalog(12) = pear +print *, store_catalog(12) +</pre></div> + +<p>This code can easily be rewritten in the Fortran 90 syntax as following: +</p> +<div class="example"> +<pre class="example">! ``STRUCTURE /name/ ... END STRUCTURE'' becomes +! ``TYPE name ... END TYPE'' +TYPE item + INTEGER id + CHARACTER(LEN=200) description + REAL price +END TYPE + +! ``RECORD /name/ variable'' becomes ``TYPE(name) variable'' +TYPE(item) pear, store_catalog(100) + +! Instead of using a dot (.) to access fields of a record, the +! standard syntax uses a percent sign (%) +pear%id = 92316 +pear%description = "juicy D'Anjou pear" +pear%price = 0.15 +store_catalog(7)%id = 7831 +store_catalog(7)%description = "milk bottle" +store_catalog(7)%price = 1.2 + +! Assignments of a whole variable do not change +store_catalog(12) = pear +print *, store_catalog(12) +</pre></div> + +<p>GNU Fortran implements STRUCTURES like derived types with the following +rules and exceptions: +</p> +<ul> +<li> Structures act like derived types with the <code>SEQUENCE</code> attribute. +Otherwise they may contain no specifiers. + +</li><li> Structures may contain a special field with the name <code>%FILL</code>. +This will create an anonymous component which cannot be accessed but occupies +space just as if a component of the same type was declared in its place, useful +for alignment purposes. As an example, the following structure will consist +of at least sixteen bytes: + +<div class="smallexample"> +<pre class="smallexample">structure /padded/ + character(4) start + character(8) %FILL + character(4) end +end structure +</pre></div> + +</li><li> Structures may share names with other symbols. For example, the following +is invalid for derived types, but valid for structures: + +<div class="smallexample"> +<pre class="smallexample">structure /header/ + ! ... +end structure +record /header/ header +</pre></div> + +</li><li> Structure types may be declared nested within another parent structure. +The syntax is: +<div class="smallexample"> +<pre class="smallexample">structure /type-name/ + ... + structure [/<type-name>/] <field-list> +... +</pre></div> + +<p>The type name may be ommitted, in which case the structure type itself is +anonymous, and other structures of the same type cannot be instantiated. The +following shows some examples: +</p> +<div class="example"> +<pre class="example">structure /appointment/ + ! nested structure definition: app_time is an array of two 'time' + structure /time/ app_time (2) + integer(1) hour, minute + end structure + character(10) memo +end structure + +! The 'time' structure is still usable +record /time/ now +now = time(5, 30) + +... + +structure /appointment/ + ! anonymous nested structure definition + structure start, end + integer(1) hour, minute + end structure + character(10) memo +end structure +</pre></div> + +</li><li> Structures may contain <code>UNION</code> blocks. For more detail see the +section on <a href="UNION-and-MAP.html#UNION-and-MAP">UNION and MAP</a>. + +</li><li> Structures support old-style initialization of components, like +those described in <a href="Old_002dstyle-variable-initialization.html#Old_002dstyle-variable-initialization">Old-style variable initialization</a>. For array +initializers, an initializer may contain a repeat specification of the form +<code><literal-integer> * <constant-initializer></code>. The value of the integer +indicates the number of times to repeat the constant initializer when expanding +the initializer list. +</li></ul> + +<hr> +<div class="header"> +<p> +Next: <a href="UNION-and-MAP.html#UNION-and-MAP" accesskey="n" rel="next">UNION and MAP</a>, Previous: <a href="Read_002fWrite-after-EOF-marker.html#Read_002fWrite-after-EOF-marker" accesskey="p" rel="previous">Read/Write after EOF marker</a>, Up: <a href="Extensions-implemented-in-GNU-Fortran.html#Extensions-implemented-in-GNU-Fortran" accesskey="u" rel="up">Extensions implemented in GNU Fortran</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> |