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

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

NAME         top

       qsort, qsort_r - sort an array

SYNOPSIS         top

       #include <stdlib.h>

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

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

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       qsort_r(): _GNU_SOURCE

DESCRIPTION         top

       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.

       The qsort_r() function is identical to qsort() except that the
       comparison function compar takes a third argument.  A pointer is
       passed to the comparison function via arg.  In this way, the
       comparison function does not need to use global variables to pass
       through arbitrary arguments, and is therefore reentrant and safe to
       use in threads.

RETURN VALUE         top

       The qsort() and qsort_r() functions return no value.

VERSIONS         top

       qsort_r() was added to glibc in version 2.8.

CONFORMING TO         top

       The qsort() function conforms to SVr4, 4.3BSD, C89, C99.

NOTES         top

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

EXAMPLE         top

       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         top

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

COLOPHON         top

       This page is part of release 3.65 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/.

                                 2012-03-08                         QSORT(3)