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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>

       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;

           if (argc < 2) {
            fprintf(stderr, "Usage: %s <string>...\n", argv[0]);
            exit(EXIT_FAILURE);
           }

           qsort(&argv[1], argc - 1, sizeof(argv[1]), 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 3.35 of the Linux man-pages project.  A  description  of  the
       project,  and information about reporting bugs, can be found at http://man7.org/linux/man-
       pages/.

                                            2009-09-15                                   QSORT(3)