memmove,memcpy,memset的实现

memmove,memcpy,mecset在库函数都是有的，可以直接使用，需要引用头文件

#include<memory.h>
#include<string.h>

void * memcpy ( void * destination, const void * source, size_t num );

void * memset ( void * ptr, int value, size_t num );

void * memmove ( void * destination, const void * source, size_t num );

num都是字节大小！

它们的格式都是

1.memcpy的实现

#include<stdio.h>
#include<assert.h>
#include<stdlib.h>
#include<memory.h>
void* my_memmove(void* arr1, void* arr2, int size) {
	assert(arr1);//防止为空指针
	assert(arr2);
	void* ret = arr1;
	while (size--) {
		*(char*)arr1 = *(char*)arr2;
		arr1 = (char*)arr1 + 1;
		arr2 = (char*)arr2 + 1;
	}
	return ret;
}
int main() {
	int arr1[20];
	int arr2[20];
	scanf("%s%s", arr1, arr2);
	printf("%s", my_memmove(arr1, arr2, 20));//20为字节大小
	return 0;
}

2.memmove的实现

#include<stdio.h>
#include<assert.h>
#include<stdlib.h>
#include<memory.h>
void* my_memmove(void* arr1, void* arr2, int size) {
	assert(arr1);
	assert(arr2);
	void* ret = arr1;
	if (ret <= arr2)
	{
		while (size--) {
			*(char*)arr1 = *(char*)arr2;
			arr1 = (char*)arr1 + 1;
			arr2 = (char*)arr2 + 1;
		}
	}
	else {
		void* src = (char*)arr2 + size - 1;
		void* des = (char*)arr1 + size - 1;
		while (size--) {
			*(char*)des = *(char*)src;
			des = (char*)des - 1;
			src = (char*)src - 1;
		}
	}
	return ret;
}
int main() {
	char arr1[20];
	char arr2[20];
	scanf("%s%s", arr1, arr2);
	printf("%s", my_memmove(arr1, arr2, 8));
	return 0;
}

3.memset的实现

#include<stdio.h>
#include<assert.h>
#include<stdlib.h>
#include<memory.h>
void* my_memset(void* arr1, int x, int size) {
	assert(arr1);
	int i = 0;
	char* ret =(char*)arr1;
	while (size--) {
		ret[i++] = x;	
	}
	return ret;
}
int main() {
	char arr1[20];
	scanf("%s", arr1);
	puts(my_memset(arr1,'1', 8));
	return 0;
}