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<h1 id="firstHeading" class="firstHeading">va_copy</h1> <table class="t-dcl-begin"> <tr class="t-dsc-header"> <th> Defined in header <code><stdarg.h></code> </th> <th> </th> <th> </th> </tr> <tr class="t-dcl t-since-c99"> <td> <pre data-language="c">void va_copy( va_list dest, va_list src );</pre>
</td> <td class="t-dcl-nopad"> </td> <td> <span class="t-mark-rev t-since-c99">(since C99)</span> </td> </tr> </table> <p>The <code>va_copy</code> macro copies <code>src</code> to <code>dest</code>.</p>
<p><code>va_end</code> should be called on <code>dest</code> before the function returns or any subsequent re-initialization of <code>dest</code> (via calls to <code>va_start</code> or <code>va_copy</code>).</p>
<h3 id="Parameters"> Parameters</h3> <table class="t-par-begin"> <tr class="t-par"> <td> dest </td> <td> - </td> <td> an instance of the <code>va_list</code> type to initialize </td>
</tr> <tr class="t-par"> <td> src </td> <td> - </td> <td> the source <code>va_list</code> that will be used to initialize <code>dest</code> </td>
</tr>
</table> <h3 id="Expanded_value"> Expanded value</h3> <p>(none)</p>
<h3 id="Example"> Example</h3> <div class="t-example"> <div class="c source-c"><pre data-language="c">#include <stdio.h>
#include <stdarg.h>
#include <math.h>
double sample_stddev(int count, ...)
{
/* Compute the mean with args1. */
double sum = 0;
va_list args1;
va_start(args1, count);
va_list args2;
va_copy(args2, args1); /* copy va_list object */
for (int i = 0; i < count; ++i) {
double num = va_arg(args1, double);
sum += num;
}
va_end(args1);
double mean = sum / count;
/* Compute standard deviation with args2 and mean. */
double sum_sq_diff = 0;
for (int i = 0; i < count; ++i) {
double num = va_arg(args2, double);
sum_sq_diff += (num-mean) * (num-mean);
}
va_end(args2);
return sqrt(sum_sq_diff / count);
}
int main(void)
{
printf("%f\n", sample_stddev(4, 25.0, 27.3, 26.9, 25.7));
}</pre></div> <p>Possible output:</p>
<div class="text source-text"><pre data-language="c">0.920258</pre></div> </div> <h3 id="References"> References</h3> <ul>
<li> C11 standard (ISO/IEC 9899:2011): </li>
<ul><li> 7.16.1.2 The va_copy macro (p: 270) </li></ul>
<li> C99 standard (ISO/IEC 9899:1999): </li>
<ul><li> 7.15.1.2 The va_copy macro (p: 250) </li></ul>
</ul> <h3 id="See_also"> See also</h3> <table class="t-dsc-begin"> <tr class="t-dsc"> <td> <div><a href="va_arg" title="c/variadic/va arg"> <span class="t-lines"><span>va_arg</span></span></a></div> </td> <td> accesses the next variadic function argument <br> <span class="t-mark">(function macro)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><a href="va_end" title="c/variadic/va end"> <span class="t-lines"><span>va_end</span></span></a></div> </td> <td> ends traversal of the variadic function arguments <br> <span class="t-mark">(function macro)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><a href="va_list" title="c/variadic/va list"> <span class="t-lines"><span>va_list</span></span></a></div> </td> <td> holds the information needed by va_start, va_arg, va_end, and va_copy <br> <span class="t-mark">(typedef)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><a href="va_start" title="c/variadic/va start"> <span class="t-lines"><span>va_start</span></span></a></div> </td> <td> enables access to variadic function arguments <br> <span class="t-mark">(function macro)</span> </td>
</tr> <tr class="t-dsc"> <td colspan="2"> <span><a href="https://en.cppreference.com/w/cpp/utility/variadic/va_copy" title="cpp/utility/variadic/va copy">C++ documentation</a></span> for <code>va_copy</code> </td>
</tr> </table> <div class="_attribution">
<p class="_attribution-p">
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<a href="https://en.cppreference.com/w/c/variadic/va_copy" class="_attribution-link">https://en.cppreference.com/w/c/variadic/va_copy</a>
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