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<title>Variable-length Argument Lists - GNU Octave</title>
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<a name="Variable-length-Argument-Lists"></a>
<a name="Variable_002dlength-Argument-Lists"></a>
<p>
Next: <a rel="next" accesskey="n" href="Ignoring-Arguments.html#Ignoring-Arguments">Ignoring Arguments</a>,
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Up: <a rel="up" accesskey="u" href="Functions-and-Scripts.html#Functions-and-Scripts">Functions and Scripts</a>
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<h3 class="section">11.3 Variable-length Argument Lists</h3>
<p><a name="index-variable_002dlength-argument-lists-742"></a><a name="index-g_t_0040code_007bvarargin_007d-743"></a>
Sometimes the number of input arguments is not known when the function
is defined. As an example think of a function that returns the smallest
of all its input arguments. For example:
<pre class="example"> a = smallest (1, 2, 3);
b = smallest (1, 2, 3, 4);
</pre>
<p class="noindent">In this example both <code>a</code> and <code>b</code> would be 1. One way to write
the <code>smallest</code> function is
<pre class="example"> function val = smallest (arg1, arg2, arg3, arg4, arg5)
<var>body</var>
endfunction
</pre>
<p class="noindent">and then use the value of <code>nargin</code> to determine which of the input
arguments should be considered. The problem with this approach is
that it can only handle a limited number of input arguments.
<p>If the special parameter name <code>varargin</code> appears at the end of a
function parameter list it indicates that the function takes a variable
number of input arguments. Using <code>varargin</code> the function
looks like this
<pre class="example"> function val = smallest (varargin)
<var>body</var>
endfunction
</pre>
<p class="noindent">In the function body the input arguments can be accessed through the
variable <code>varargin</code>. This variable is a cell array containing
all the input arguments. See <a href="Cell-Arrays.html#Cell-Arrays">Cell Arrays</a>, for details on working
with cell arrays. The <code>smallest</code> function can now be defined
like this
<pre class="example"> function val = smallest (varargin)
val = min ([varargin{:}]);
endfunction
</pre>
<p class="noindent">This implementation handles any number of input arguments, but it's also
a very simple solution to the problem.
<p>A slightly more complex example of <code>varargin</code> is a function
<code>print_arguments</code> that prints all input arguments. Such a function
can be defined like this
<pre class="example"> function print_arguments (varargin)
for i = 1:length (varargin)
printf ("Input argument %d: ", i);
disp (varargin{i});
endfor
endfunction
</pre>
<p class="noindent">This function produces output like this
<pre class="example"> print_arguments (1, "two", 3);
-| Input argument 1: 1
-| Input argument 2: two
-| Input argument 3: 3
</pre>
<!-- parseparams scripts/miscellaneous/parseparams.m -->
<p><a name="doc_002dparseparams"></a>
<div class="defun">
— Function File: [<var>reg</var>, <var>prop</var>] = <b>parseparams</b> (<var>params</var>)<var><a name="index-parseparams-744"></a></var><br>
— Function File: [<var>reg</var>, <var>var1</var>, <small class="dots">...</small>] = <b>parseparams</b> (<var>params, name1, default1, <small class="dots">...</small></var>)<var><a name="index-parseparams-745"></a></var><br>
<blockquote><p>Return in <var>reg</var> the cell elements of <var>param</var> up to the first
string element and in <var>prop</var> all remaining elements beginning
with the first string element. For example:
<pre class="example"> [reg, prop] = parseparams ({1, 2, "linewidth", 10})
reg =
{
[1,1] = 1
[1,2] = 2
}
prop =
{
[1,1] = linewidth
[1,2] = 10
}
</pre>
<p>The parseparams function may be used to separate 'regular'
arguments and additional arguments given as property/value pairs of
the <var>varargin</var> cell array.
<p>In the second form of the call, available options are specified directly
with their default values given as name-value pairs.
If <var>params</var> do not form name-value pairs, or if an option occurs
that does not match any of the available options, an error occurs.
When called from an m-file function, the error is prefixed with the
name of the caller function.
The matching of options is case-insensitive.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dvarargin.html#doc_002dvarargin">varargin</a>.
</p></blockquote></div>
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