Qsort function and Simulation Implementation of qsort function

Catalog ：

qsort Function and Simulation Implementation qsort function

1.qsort function

2. Simulation Implementation qsort function

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qsort function

Using the idea of quick sort to achieve a sort function .

qsort Use the four parameters you need ：

① The starting address of the data to be sorted

② The number of data elements to be sorted

③ The size of the data elements to be sorted , Unit byte

④ A function pointer —— Comparison function

int (*cmp)(const void* e1,const void* e2)

Simulation demonstration qsort Use of functions ：

Sort the numbers

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

int int_cmp(const void* p1, const void* p2)
{
	return (*(int*)p1 - *(int*)p2);
}

int main()
{
	int arr[] = { 1,3,5,7,9,2,4,6,8,0 };

	int sz = sizeof(arr) / sizeof(arr[0]);

	int i = 0;

	qsort(arr, sz, sizeof(arr[0]), int_cmp);

	for (i = 0; i < sz; i++)
	{
		printf("%d ", arr[i]);
	}

	return 0;
} 

Dissect the code ：

function ：int_cmp The ascending and descending order of

Sort structure

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

struct stu
{
	char name[20];
	int age;
};

int int_cmp_name(const void* e1, const void* e2)
{
	return strcmp(((struct stu*)e1)->name, ((struct stu*)e2)->name);
}
int int_cmp_age(const void* e1, const void* e2)
{
	return strcmp(((struct stu*)e1)->age, ((struct stu*)e2)->age);
}

int main()
{
	struct stu s[] = { {"zhang",15},{"li",30},{"wang",25} };

	int sz = sizeof(s) / sizeof(s[0]);

	qsort(s, sz, sizeof(s[0]), int_cmp_name);

	qsort(s, sz, sizeof(s[0]), int_cmp_age);

	return 0;
}

Particular attention ：

for example ：

int a=10;

char* pa=&a; Report errors

void* pb=&a; That's all right.

void* Is a pointer without a specific type , Can receive any type of address , Can't dereference , You can't +- Integers

Compare the size

① Number comparison ：30>25>15

② Letter comparison ： abcd > abbe;b>c

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Simulation Implementation qsort function

#include <stdio.h>

int int_cmp(const void* e1, const void* e2)
{
	return (*(int*)e1 - *(int*)e2);
}

void swap(char* e1, char* e2,int width)
{
	int i = 0;
	for (i = 0; i < width; i++)
	{
		char tmp = *e1;
		*e1 = *e2;
		*e2 = tmp;
		e1++;
		e2++;
	}
}

void bubble(void* base, int count, int width, int(*cmp)(void*, void*))
{
	int i = 0;
	int j = 0;
	for (i = 0; i < count-1; i++)
	{
		int flag = 1;
		for (j = 0; j < count - 1 - i; j++)
		{
			if (cmp((char*)base + j * width, (char*)base + (j + 1) * width) > 0)
			{
				swap((char*)base + j * width, (char*)base + (j + 1) * width, width);
				flag = 0;
			}
		}
		if (flag == 0)
			break;
	}
}

int main()
{
	int arr[] = { 1,3,5,7,9,2,4,6,8,0 };
	
	int sz = sizeof(arr) / sizeof(arr[0]);

	int i = 0;

	bubble(arr, sz, sizeof(arr[0]), int_cmp);

	for (i = 0; i < sz; i++)
	{
		printf("%d ", arr[i]);
	}

	return 0;
}

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Conclusion ：

If it helps you ,

Don't forget it give the thumbs-up + Focus on Oh , Crab

If it helps you ,

Don't forget it give the thumbs-up + Focus on Oh , Crab

If it helps you ,

Don't forget it give the thumbs-up + Focus on Oh , Crab