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<a name="Calling-Octave-Functions-from-Oct_002dFiles"></a>
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<p>
Next: <a href="Calling-External-Code-from-Oct_002dFiles.html#Calling-External-Code-from-Oct_002dFiles" accesskey="n" rel="next">Calling External Code from Oct-Files</a>, Previous: <a href="Accessing-Global-Variables-in-Oct_002dFiles.html#Accessing-Global-Variables-in-Oct_002dFiles" accesskey="p" rel="prev">Accessing Global Variables 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>
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<hr>
<a name="Calling-Octave-Functions-from-Oct_002dFiles-1"></a>
<h4 class="subsection">A.1.8 Calling Octave Functions from Oct-Files</h4>
<p>There is often a need to be able to call another Octave function from
within an oct-file, and there are many examples of such within Octave
itself. For example, the <code>quad</code> function is an oct-file that
calculates the definite integral by quadrature over a user supplied
function.
</p>
<p>There are also many ways in which a function might be passed. It might
be passed as one of
</p>
<ol>
<li> Function Handle
</li><li> Anonymous Function Handle
</li><li> Inline Function
</li><li> String
</li></ol>
<p>The example below demonstrates an example that accepts all four means of
passing a function to an oct-file.
</p>
<div class="example">
<pre class="verbatim">#include <octave/oct.h>
#include <octave/parse.h>
DEFUN_DLD (funcdemo, args, nargout, "Function Demo")
{
octave_value_list retval;
int nargin = args.length ();
if (nargin < 2)
print_usage ();
else
{
octave_value_list newargs;
for (octave_idx_type i = nargin - 1; i > 0; i--)
newargs(i-1) = args(i);
if (args(0).is_function_handle () || args(0).is_inline_function ())
{
octave_function *fcn = args(0).function_value ();
if (! error_state)
retval = feval (fcn, newargs, nargout);
}
else if (args(0).is_string ())
{
std::string fcn = args(0).string_value ();
if (! error_state)
retval = feval (fcn, newargs, nargout);
}
else
error ("funcdemo: INPUT must be string, inline, or function handle");
}
return retval;
}
</pre><pre class="example">
</pre></div>
<p>The first argument to this demonstration is the user-supplied function
and the remaining arguments are all passed to the user function.
</p>
<div class="example">
<pre class="example">funcdemo (@sin,1)
⇒ 0.84147
funcdemo (@(x) sin (x), 1)
⇒ 0.84147
funcdemo (inline ("sin (x)"), 1)
⇒ 0.84147
funcdemo ("sin",1)
⇒ 0.84147
funcdemo (@atan2, 1, 1)
⇒ 0.78540
</pre></div>
<p>When the user function is passed as a string the treatment of the
function is different. In some cases it is necessary to have the
user supplied function as an <code>octave_function</code> object. In that
case the string argument can be used to create a temporary function
as demonstrated below.
</p>
<div class="example">
<pre class="example">std::octave fcn_name = unique_symbol_name ("__fcn__");
std::string fcode = "function y = ";
fcode.append (fcn_name);
fcode.append ("(x) y = ");
fcn = extract_function (args(0), "funcdemo", fcn_name,
fcode, "; endfunction");
…
if (fcn_name.length ())
clear_function (fcn_name);
</pre></div>
<p>There are two important things to know in this case. First, the number of
input arguments to the user function is fixed, and in the above example is
a single argument. Second, to avoid leaving the temporary function in the
Octave symbol table it should be cleared after use. Also, by convention
internal function names begin and end with the character sequence ‘<samp>__</samp>’.
</p>
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<div class="header">
<p>
Next: <a href="Calling-External-Code-from-Oct_002dFiles.html#Calling-External-Code-from-Oct_002dFiles" accesskey="n" rel="next">Calling External Code from Oct-Files</a>, Previous: <a href="Accessing-Global-Variables-in-Oct_002dFiles.html#Accessing-Global-Variables-in-Oct_002dFiles" accesskey="p" rel="prev">Accessing Global Variables 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>
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