<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <!-- Created by GNU Texinfo 6.5, http://www.gnu.org/software/texinfo/ --> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <title>Structures in Oct-Files (GNU Octave (version 5.1.0))</title> <meta name="description" content="Structures in Oct-Files (GNU Octave (version 5.1.0))"> <meta name="keywords" content="Structures in Oct-Files (GNU Octave (version 5.1.0))"> <meta name="resource-type" content="document"> <meta name="distribution" content="global"> <meta name="Generator" content="makeinfo"> <link href="index.html#Top" rel="start" title="Top"> <link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index"> <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> <link href="Oct_002dFiles.html#Oct_002dFiles" rel="up" title="Oct-Files"> <link href="Sparse-Matrices-in-Oct_002dFiles.html#Sparse-Matrices-in-Oct_002dFiles" rel="next" title="Sparse Matrices in Oct-Files"> <link href="Cell-Arrays-in-Oct_002dFiles.html#Cell-Arrays-in-Oct_002dFiles" rel="prev" title="Cell Arrays in Oct-Files"> <style type="text/css"> <!-- a.summary-letter {text-decoration: none} blockquote.indentedblock {margin-right: 0em} blockquote.smallindentedblock {margin-right: 0em; font-size: smaller} blockquote.smallquotation {font-size: smaller} div.display {margin-left: 3.2em} div.example {margin-left: 3.2em} div.lisp {margin-left: 3.2em} div.smalldisplay {margin-left: 3.2em} div.smallexample {margin-left: 3.2em} 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.nolinebreak {white-space: nowrap} span.roman {font-family: initial; font-weight: normal} span.sansserif {font-family: sans-serif; font-weight: normal} ul.no-bullet {list-style: none} --> </style> <link rel="stylesheet" type="text/css" href="octave.css"> </head> <body lang="en"> <a name="Structures-in-Oct_002dFiles"></a> <div class="header"> <p> Next: <a href="Sparse-Matrices-in-Oct_002dFiles.html#Sparse-Matrices-in-Oct_002dFiles" accesskey="n" rel="next">Sparse Matrices in Oct-Files</a>, Previous: <a href="Cell-Arrays-in-Oct_002dFiles.html#Cell-Arrays-in-Oct_002dFiles" accesskey="p" rel="prev">Cell Arrays in Oct-Files</a>, Up: <a href="Oct_002dFiles.html#Oct_002dFiles" accesskey="u" rel="up">Oct-Files</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> </div> <hr> <a name="Structures-in-Oct_002dFiles-1"></a> <h4 class="subsection">A.1.5 Structures in Oct-Files</h4> <p>A structure in Octave is a map between a number of fields represented and their values. The Standard Template Library <code>map</code> class is used, with the pair consisting of a <code>std::string</code> and an Octave <code>Cell</code> variable. </p> <p>A simple example demonstrating the use of structures within oct-files is </p> <div class="example"> <pre class="verbatim">#include <octave/oct.h> #include <octave/ov-struct.h> DEFUN_DLD (structdemo, args, , "Struct Demo") { if (args.length () != 2) print_usage (); if (! args(0).isstruct ()) error ("structdemo: ARG1 must be a struct"); octave_scalar_map arg0 = args(0).scalar_map_value (); //octave_map arg0 = args(0).map_value (); if (! args(1).is_string ()) error ("structdemo: ARG2 must be a character string"); std::string arg1 = args(1).string_value (); octave_value tmp = arg0.contents (arg1); //octave_value tmp = arg0.contents (arg1)(0); if (! tmp.is_defined ()) error ("structdemo: struct does not have a field named '%s'\n", arg1.c_str ()); octave_scalar_map st; st.assign ("selected", tmp); return octave_value (st); } </pre></div> <p>An example of its use is </p> <div class="example"> <pre class="example">x.a = 1; x.b = "test"; x.c = [1, 2]; structdemo (x, "b") ⇒ selected = test </pre></div> <p>The example above specifically uses the <code>octave_scalar_map</code> class which is for representing a single struct. For structure arrays, the <code>octave_map</code> class is used instead. The commented code shows how the demo could be modified to handle a structure array. In that case, the <code>contents</code> method returns a <code>Cell</code> which may have more than one element. Therefore, to obtain the underlying <code>octave_value</code> in the single struct example we would write </p> <div class="example"> <pre class="example">octave_value tmp = arg0.contents (arg1)(0); </pre></div> <p>where the trailing <code>(0)</code> is the <code>()</code> operator on the <code>Cell</code> object. If this were a true structure array with multiple elements we could iterate over the elements using the <code>()</code> operator. </p> <p>Structures are a relatively complex data container and there are more functions available in <samp>oct-map.h</samp> which make coding with them easier than relying on just <code>contents</code>. </p> <hr> <div class="header"> <p> Next: <a href="Sparse-Matrices-in-Oct_002dFiles.html#Sparse-Matrices-in-Oct_002dFiles" accesskey="n" rel="next">Sparse Matrices in Oct-Files</a>, Previous: <a href="Cell-Arrays-in-Oct_002dFiles.html#Cell-Arrays-in-Oct_002dFiles" accesskey="p" rel="prev">Cell Arrays in Oct-Files</a>, Up: <a href="Oct_002dFiles.html#Oct_002dFiles" accesskey="u" rel="up">Oct-Files</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> </div> </body> </html>