Quick sort function in C language -- qsort

Function name

qsort();

The header file

#include<stdlib,h>

function

Quick sort the elements in the array in ascending order by default

Function declaration

void qsort( void *buf, size_t num, size_t size, int (*compare)(const void *, const void *) );

//eg
// Take ascending order 
int compare(const void* a, const void* b) {
    
	int* s1 = (int*)a;
	int* s2 = (int*)b;
	return *s1 - *s2;
}

int n = 9;
int arr[n];
// Suppose that all the data in the array is input 
qsort(arr, n, sizeof(int), compare);

buf Is the name of the array to be sorted , It can be an array of characters , integer array , Array of structs … As long as you can compare the size

num Is the number of array elements

size Is the number of bytes occupied by a single element , for example int yes sizeof(int)

compare Is a function that compares sizes , The return value is int, You need to write it yourself
int compare(const void a, const void b)

a and b All are void The variable of , It's a weak type , The system doesn't know what they point to , So when using, you should first convert the type to the required pointer type *

If the function compare The first parameter of is less than the second parameter , Returns a negative value ; Return zero if equal to ; If greater than return positive . Function pair buf The data pointed to is sorted in ascending order .