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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head> <meta name="generator" content= "HTML Tidy for Linux/x86 (vers 1 September 2005), see www.w3.org"> <title>qsort</title> <link href="../cppreference.css" rel="stylesheet" type="text/css"></head><body><table> <tr> <td> <div class="body-content"> <div class="header-box"> <a href="../index.html">cppreference.com</a> > <a href= "index.html">Other Standard C Functions</a> > <a href= "qsort.html">qsort</a> </div> <div class="name-format"> qsort </div> <div class="syntax-name-format"> Syntax: </div> <pre class="syntax-box"> #include <stdlib.h> void qsort( void *buf, size_t num, size_t size, int (*compare)(const void *, const void *) );</pre> <p>The qsort() function sorts <em>buf</em> (which contains <em>num</em> items, each of size <em>size</em>) using <a href= "http://en.wikipedia.org/wiki/Quicksort">Quicksort</a>. The <em>compare</em> function is used to compare the items in <em>buf</em>. <em>compare</em> should return negative if the first argument is less than the second, zero if they are equal, and positive if the first argument is greater than the second. qsort() sorts <em>buf</em> in ascending order.</p> <div class="related-examples-format"> Example code: </div> <div class="related-examples"> <p>For example, the following bit of code uses qsort() to sort an array of integers:</p> <pre class="example-code"> int compare_ints( const void* a, const void* b ) { int* arg1 = (int*) a; int* arg2 = (int*) b; if( *arg1 < *arg2 ) return -1; else if( *arg1 == *arg2 ) return 0; else return 1; } int array[] = { -2, 99, 0, -743, 2, 3, 4 }; int array_size = 7; ... printf( "Before sorting: " ); for( int i = 0; i < array_size; i++ ) { printf( "%d ", array[i] ); } printf( "\n" ); qsort( array, array_size, sizeof(int), compare_ints ); printf( "After sorting: " ); for( int i = 0; i < array_size; i++ ) { printf( "%d ", array[i] ); } printf( "\n" ); </pre> <p>When run, this code displays the following output:</p> <pre class="example-code"> Before sorting: -2 99 0 -743 2 3 4 After sorting: -743 -2 0 2 3 4 99 </pre> </div> <div class="related-name-format"> Related topics: </div> <div class="related-content"> <a href="bsearch.html">bsearch</a><br> (C++ Algorithms) <a href="../cppalgorithm/sort.html">sort</a> </div> </div> </td> </tr> </table></body></html>⌨️ 快捷键说明
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