• 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>
  #include <assert.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;
  
      assert(argc > 1);
  
      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 3.19 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/.

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