C语言中memcpy、memset和memmove的实现

1) memcpy():

主要实现的是两段内存的复制

2) memset():

实现对一段内存进行初始化

3)memmove():

主要是实现一段内存的内容移动到另一段内存。

实现的代码如下：

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

void* Mymemcpy(void* dest, const void* src, unsigned int size)
{
	unsigned int i = 0;
	char* p = (char*)dest;
	char* q = (char*)src;
	assert(dest != NULL && src != NULL);
	if(size > 0)
	{
		while((i < size) && (*(p + i) = *(q + i)))
			i++;
		return dest;
	}
	return NULL;
}

void* Mymemset(void* dest, int ch, unsigned int size)
{
	unsigned int i = 0;
	unsigned char* p = (unsigned char*)dest;
	while((i < size) && (*(p + i) = ch))
	{
		i++;
	}
	return dest;
}

void* Mymemmove(void* dst, const void* src, unsigned int count)
{
	void *ret = dst;
	if(dst <= src || (char*)dst >= ((char*)src + count))
	{
		while(count--)
		{
			*(char*)dst = *(char*)src;
			dst = (char*)dst + 1;
			src = (char*)src + 1;
		}
	}
	else
	{
		dst = (char*)dst + count - 1;
		src = (char*)src + count - 1;
		while(count--)
		{
			*(char*)dst = *(char*)src;
			dst = (char*)dst - 1;
			src = (char*)src - 1;
		}
	}
	return(ret);
}
int main()
{
	int size;
	char* p = (char*)malloc(10 * sizeof(char));
	char* dst = (char*)malloc(5 * sizeof(char));
	Mymemset(p,'a',10);
	puts(p);

	Mymemmove(dst, p, 5);
	puts(dst);

	system("pause");
	return 0;
}