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qsort.3

QSORT

Section: Linux Programmer's Manual (3)
Updated: 2009-02-01
Index Return to Main Contents
 

NAME

qsort - sorts an array  

SYNOPSIS

#include <stdlib.h>

void qsort(void *base, size_t nmemb, size_t size,
           int(*compar)(const void *, const void *));
 

DESCRIPTION

The qsort() function sorts an array with nmemb elements of size size. The base argument points to the start of the array.

The contents of the array are sorted in ascending order according to a comparison function pointed to by compar, which is called with two arguments that point to the objects being compared.

The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second. If two members compare as equal, their order in the sorted array is undefined.  

RETURN VALUE

The qsort() function returns no value.  

CONFORMING TO

SVr4, 4.3BSD, C89, C99.  

NOTES

Library routines suitable for use as the compar argument include alphasort(3) and versionsort(3). To compare C strings, the comparison function can call strcmp(3), as shown in the example below.  

EXAMPLE

For one example of use, see the example under bsearch(3).

Another example is the following program, which sorts the strings given in its command-line arguments:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

static int
cmpstringp(const void *p1, const void *p2)
{
    /* The actual arguments to this function are "pointers to
       pointers to char", but strcmp(3) arguments are "pointers
       to char", hence the following cast plus dereference */

    return strcmp(* (char * const *) p1, * (char * const *) p2);
}

int
main(int argc, char *argv[])
{
    int j;

    assert(argc > 1);

    qsort(&argv[1], argc - 1, sizeof(char *), cmpstringp);

    for (j = 1; j < argc; j++)
        puts(argv[j]);
    exit(EXIT_SUCCESS);
}
 

SEE ALSO

sort(1), alphasort(3), strcmp(3), versionsort(3)  

COLOPHON

This page is part of release 3.21 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
CONFORMING TO
NOTES
EXAMPLE
SEE ALSO
COLOPHON

 

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