qsort函数和bsearch函数的使用

1.qsort排序

/* qsort example */
#include <stdio.h>
#include <stdlib.h>

int values[] = { 40, 10, 100, 90, 20, 25 };

int compare (const void * a, const void * b)
{
  return ( *(int*)a - *(int*)b );
}

int main ()
{
  int n;
  qsort (values, 6, sizeof(int), compare);
  for (n=0; n<6; n++)
     printf ("%d ",values[n]);
  return 0;
}

Output:

10 20 25 40 90 100

2.bsearch查找：

/* bsearch example */
#include <stdio.h>
#include <stdlib.h>

int compareints (const void * a, const void * b)
{
  return ( *(int*)a - *(int*)b );
}

int values[] = { 10, 20, 25, 40, 90, 100 };

int main ()
{
  int * pItem;
  int key = 40;
  pItem = (int*) bsearch (&key, values, 6, sizeof (int), compareints);
  if (pItem!=NULL)
    printf ("%d is in the array.\n",*pItem);
  else
    printf ("%d is not in the array.\n",key);
  return 0;
}
 

Output:

40 is in the array

3.两者结合用法：

/* bsearch example with strings */
#include <stdio.h>
#include <stdlib.h>

char strvalues[][20] = {"some","example","strings","here"};

int main ()
{
  char * pItem;
  char key[20] = "example";

  /* sort elements in array: */
  qsort (strvalues, 4, 20, (int(*)(const void*,const void*)) strcmp);

  /* search for the key: */
  pItem = (char*) bsearch (key, strvalues, 4, 20, (int(*)(const void*,const void*)) strcmp);

  if (pItem!=NULL)
    printf ("%s is in the array.\n",pItem);
  else
    printf ("%s is not in the array.\n",key);
  return 0;
}

说明：

void qsort ( void * base, size_t num, size_t size, int ( * comparator ) ( const void *, const void * ) );
void * bsearch ( const void * key, const void * base, size_t num, size_t size, int ( * comparator ) ( const void *, const void * ) );

更多请参考：http://www.cplusplus.com/reference/clibrary/cstdlib/qsort/