C library function - qsort()

describe

C Library function void qsort(void *base, size_t nitems, size_t size, int (*compar)(const void *, const void*))  Sort the array .

Statement

Here is qsort() Declaration of functions .

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

Parameters

base: Array to sort
nmemb: The number of elements in the array
size: Each array element takes up memory space , You can use sizeof get
compar: A comparison function that compares two array elements . The value of the first parameter of this comparison function is less than 、 be equal to 、 When it is greater than the value of the second parameter , The return values of this comparison function should be less than 、 be equal to 、 Greater than zero .

That is to say, you need to implement such a function （ Ascending ）：
int cmp(const void *a, const void *b)
If a > b, return >0
If a == b, return 0
If a < b, return <0
there a and b The relationship between is only logical , It's not worth comparison , So sorting can be more than numbers , It can also be characters .

Return value

This function does not return any value .

example

The following example demonstrates qsort() Function usage .

example

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

int values[] = { 88, 56, 100, 2, 25 };

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

int main()
{
   int n;

   printf(" Sort the previous list ：\n");
   for( n = 0 ; n < 5; n++ ) {
      printf("%d ", values[n]);
   }

   qsort(values, 5, sizeof(int), cmpfunc);

   printf("\n Sorted list ：\n");
   for( n = 0 ; n < 5; n++ ) {
      printf("%d ", values[n]);
   }
 
  return(0);
}

Let's compile and run the above program , This will produce the following results ：

 Sort the previous list ：
88 56 100 2 25 
 Sorted list ：
2 25 56 88 100