QSORT(3)                                            Linux Programmer's Manual                                           QSORT(3)



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 consid-
       ered 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(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 3.25 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/.



                                                           2009-09-15                                                   QSORT(3)