qsort(3) - Linux manual page (original) (raw)

qsort(3) Library Functions Manual qsort(3)

NAME top

   qsort, qsort_r - sort an array

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#include <stdlib.h>**

   **void qsort(void** _base_**[.**_size_ *** .**_n_**], size_t** _n_**, size_t** _size_**,**
              **typeof(int (const void [.**_size_**], const void [.**_size_**]))**
                  *****_compar_**);**
   **void qsort_r(void** _base_**[.**_size_ *** .**_n_**], size_t** _n_**, size_t** _size_**,**
              **typeof(int (const void [.**_size_**], const void [.**_size_**], void *))**
                  *****_compar_**,**
              **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 _n_ 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.

ATTRIBUTES top

   For an explanation of the terms used in this section, see
   [attributes(7)](../man7/attributes.7.html).
   ┌──────────────────────────────────────┬───────────────┬─────────┐
   │ **Interface** │ **Attribute** │ **Value** │
   ├──────────────────────────────────────┼───────────────┼─────────┤
   │ **qsort**(), **qsort_r**()                   │ Thread safety │ MT-Safe │
   └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS top

   **qsort**()
          C11, POSIX.1-2008.

HISTORY top

   **qsort**()
          POSIX.1-2001, C89, SVr4, 4.3BSD.

   **qsort_r**()
          glibc 2.8.

NOTES top

   To compare C strings, the comparison function can call [strcmp(3)](../man3/strcmp.3.html),
   as shown in the example below.

EXAMPLES top

   For one example of use, see the example under [bsearch(3)](../man3/bsearch.3.html).

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

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

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

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

SEE ALSO top

   [sort(1)](../man1/sort.1.html), [alphasort(3)](../man3/alphasort.3.html), [strcmp(3)](../man3/strcmp.3.html), [versionsort(3)](../man3/versionsort.3.html)

COLOPHON top

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Linux man-pages 6.10 2024-12-13 qsort(3)

Pages that refer to this page:bsearch(3), fts(3), scandir(3), tsearch(3)