Syntax

#include <stdlib.h>
void qsort(void *base, size_t num, size_t width,
           int(*compare)(const void *key, const void *element));

qsort sorts an array of num elements, each of width bytes in size. The base pointer is a pointer to the array to be sorted. qsort overwrites this array with the sorted elements.

The compare argument is a pointer to a function you must supply that takes a pointer to the key argument and to an array element, in that order. qsort calls this function one or more times during the search. The function must compare the key and the element and return one of the following values: compact break=fit.

Value

Meaning
Less than 0
key less than element
0
key equal to element
Greater than 0
key greater than element

The sorted array elements are stored in ascending order, as defined by your compare function. You can sort in reverse order by reversing the sense of "greater than" and "less than" in compare. The order of the elements is unspecified when two elements compare equally.

There is no return value.

This example sorts the arguments (argv) in ascending lexical sequence, using the comparison function compare() supplied in the example.

#include <stdio.h>#include <stdlib.h>
#include <string.h>

/* --------------------------------------------------------------             */
/* compare() routine called internally by qsort()                             */
/* --------------------------------------------------------------             */

int compare(const void *arg1,const void *arg2)
{
   return (strcmp(*(char **)arg1, *(char **)arg2));
}

int main(int argc,char *argv[])
{
   int i;
   argv++;
   argc--;

   qsort((char *)argv, argc, sizeof(char *), compare);
   for (i = 0; i < argc; ++i)
      printf("%s\n", argv[i]);
   return 0;

   /****************************************************************************
      Assuming command line of: qsort kent theresa andrea laura brenden
      Output should be:

        andrea
        brenden
        kent
        laura
        theresa
   ****************************************************************************/
}

• bsearch
  
• lfind - lsearch

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