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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

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                                  2009-09-15                          QSORT(3)