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<p>Allows a function to accept any number of arguments.
</p><p>Indicated by the parameter of the form <span class="t-c"><span class="mw-geshi cpp source-cpp">...</span></span> which must appear last in the <span class="t-spar">parameter-list</span> of a <a href="function.html" title="cpp/language/function">function declaration</a>.
</p><p>Where syntactically correct, <span class="t-c"><span class="mw-geshi cpp source-cpp">, ...</span></span> may be replaced by <span class="t-c"><span class="mw-geshi cpp source-cpp">...</span></span>.
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co1">// the function declared as follows</span>
<span class="kw4">int</span> printx<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> fmt, ...<span class="br0">)</span><span class="sy4">;</span>
<span class="co1">// may be called with one or more arguments:</span>
printx<span class="br0">(</span><span class="st0">"hello world"</span><span class="br0">)</span><span class="sy4">;</span>
printx<span class="br0">(</span><span class="st0">"a=%d b=%d"</span>, a, b<span class="br0">)</span><span class="sy4">;</span>
 
<span class="kw4">int</span> printx<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> fmt...<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// same as above (comma is optional)</span>
<span class="kw4">int</span> printy<span class="br0">(</span>..., <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> fmt<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// error: ... must be the last</span>
<span class="kw4">int</span> printz<span class="br0">(</span>...<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// valid, but the arguments cannot be accessed portably</span></pre></div></div>
<p>Note: this is different from a function <a href="parameter_pack.html" title="cpp/language/parameter pack">parameter pack</a> expansion, which is indicated by an ellipsis that is a part of a parameter declarator, rather than an ellipsis that appears as a parameter on its own. Both parameter pack expansion and the ellipsis parameter may appear in the declaration of a function template, as in the case of <span class="t-lc"><a href="../types/is_function.html" title="cpp/types/is function">std::is_function</a></span>.
</p>
<table id="toc" class="toc"><tr><td><div id="toctitle"><h2>Contents</h2></div>
<ul>
<li class="toclevel-1 tocsection-1"><a href="variadic_arguments.html#Default_conversions"><span class="tocnumber">1</span> <span class="toctext">Default conversions</span></a></li>
<li class="toclevel-1 tocsection-2"><a href="variadic_arguments.html#Alternatives"><span class="tocnumber">2</span> <span class="toctext">Alternatives</span></a></li>
<li class="toclevel-1 tocsection-3"><a href="variadic_arguments.html#Notes"><span class="tocnumber">3</span> <span class="toctext">Notes</span></a></li>
<li class="toclevel-1 tocsection-4"><a href="variadic_arguments.html#See_also"><span class="tocnumber">4</span> <span class="toctext">See also</span></a></li>
</ul>
</td></tr></table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/variadic_arguments&action=edit&section=1" title="Edit section: Default conversions">edit</a>]</span> <span class="mw-headline" id="Default_conversions">Default conversions</span></h3>
<p>When a variadic function is called, after lvalue-to-rvalue, array-to-pointer, and function-to-pointer <a href="implicit_cast.html#Lvalue_transformations" title="cpp/language/implicit cast">conversions</a>, each argument that is a part of the variable argument list undergoes additional conversions known as <i>default argument promotions</i>:
</p>
<ul><li> <span class="t-lc"><a href="../types/nullptr_t.html" title="cpp/types/nullptr t">std::nullptr_t</a></span> is converted to <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span></span></span>
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span></span></span> arguments are converted to <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span> as in <a href="implicit_cast.html#Floating_point_promotion" title="cpp/language/implicit cast">floating-point promotion</a>
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char</span></span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">short</span></span></span>, and unscoped enumerations are converted to <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span></span></span> or wider integer types as in <a href="implicit_cast.html#Integer_promotion" title="cpp/language/implicit cast">integer promotion</a>
</li></ul>
<p>Only arithmetic, enumeration, pointer, pointer to member, and class type arguments are allowed.
</p><p>Because variadic parameters have the lowest rank for the purpose of <a href="overload_resolution.html" title="cpp/language/overload resolution">overload resolution</a>, they are commonly used as the catch-all fallbacks in <a href="sfinae.html" title="cpp/language/sfinae">SFINAE</a>.
</p><p>Within the body of a function that uses variadic arguments, the values of these arguments may be accessed using the <a href="../utility/variadic.html" title="cpp/utility/variadic"><cstdarg> library facilities</a>:
</p>
<table class="t-dsc-begin">
<tr class="t-dsc-header">
<td colspan="2"> <div>Defined in header <code><cstdarg></code> </div>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="../utility/variadic/va_start.html" title="cpp/utility/variadic/va start"> <span class="t-lines"><span>va_start</span></span></a></div></div>
</td>
<td> enables access to variadic function arguments <br /> <span class="t-mark">(function macro)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/utility/variadic/dsc_va_start&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="../utility/variadic/va_arg.html" title="cpp/utility/variadic/va arg"> <span class="t-lines"><span>va_arg</span></span></a></div></div>
</td>
<td> accesses the next variadic function argument <br /> <span class="t-mark">(function macro)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/utility/variadic/dsc_va_arg&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="../utility/variadic/va_copy.html" title="cpp/utility/variadic/va copy"> <span class="t-lines"><span>va_copy</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div>
</td>
<td> makes a copy of the variadic function arguments <br /> <span class="t-mark">(function macro)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/utility/variadic/dsc_va_copy&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="../utility/variadic/va_end.html" title="cpp/utility/variadic/va end"> <span class="t-lines"><span>va_end</span></span></a></div></div>
</td>
<td> ends traversal of the variadic function arguments <br /> <span class="t-mark">(function macro)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/utility/variadic/dsc_va_end&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="../utility/variadic/va_list.html" title="cpp/utility/variadic/va list"> <span class="t-lines"><span>va_list</span></span></a></div></div>
</td>
<td> holds the information needed by va_start, va_arg, va_end, and va_copy <br /> <span class="t-mark">(typedef)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/utility/variadic/dsc_va_list&action=edit">[edit]</a></span>
</td></tr>
</table>
<p>The behavior of the <span class="t-lc"><a href="../utility/variadic/va_start.html" title="cpp/utility/variadic/va start">va_start</a></span> macro is undefined if the last parameter before the ellipsis has reference type, or has type that is not compatible with the type that results from default argument promotions.
</p>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/variadic_arguments&action=edit&section=2" title="Edit section: Alternatives">edit</a>]</span> <span class="mw-headline" id="Alternatives">Alternatives</span></h3>
<ul><li> <a href="parameter_pack.html" title="cpp/language/parameter pack">Variadic templates</a> can also be used to create functions that take variable number of arguments. They are often the better choice because they do not impose restrictions on the types of the arguments, do not perform integral and floating-point promotions, and are type safe. <span class="t-mark-rev t-since-cxx11">(since C++11)</span>
</li><li> If all variable arguments share a common type, a <span class="t-lc"><a href="../utility/initializer_list.html" title="cpp/utility/initializer list">std::initializer_list</a></span> provides a convenient mechanism (albeit with a different syntax) for accessing variable arguments. <span class="t-mark-rev t-since-cxx11">(since C++11)</span>
</li></ul>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/variadic_arguments&action=edit&section=3" title="Edit section: Notes">edit</a>]</span> <span class="mw-headline" id="Notes">Notes</span></h3>
<p>In the C programming language, at least one named parameter must appear before the ellipsis parameter, so <code>printz(...);</code> is not valid. In C++, this form is allowed even though the arguments passed to such function are not accessible, and is commonly used as the fallback overload in <a href="sfinae.html" title="cpp/language/sfinae">SFINAE</a>, exploiting the lowest priority of the ellipsis conversion in <a href="overload_resolution.html" title="cpp/language/overload resolution">overload resolution</a>.
</p>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/variadic_arguments&action=edit&section=4" title="Edit section: See also">edit</a>]</span> <span class="mw-headline" id="See_also">See also</span></h3>
<table class="t-dsc-begin">
<tr class="t-dsc">
<td colspan="2"> <div class="t-dsc-see"><span><a href="../../c/language/variadic.html" title="c/language/variadic">C documentation</a></span> for <span class="t-dsc-see-tt"><span>Variadic arguments</span></span></div>
</td></tr>
</table>
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