C/C++ memcpy實作

資料來源:https://mp.weixin.qq.com/s/lZ9SsObIMoncjs4ZoyLRlA

線上編譯:https://www.tutorialspoint.com/compile_c_online.php

Code:

#include <stdio.h>
#include <string.h>

void *sky_memecpy_1(void *dst, const void *str, int n)
{
	if (NULL == dst || NULL == str || n <= 0)
	{
		return NULL;
	}
	
	char *pdst = (char *)dst;
	char *pstr = (char *)str;
	while (n --)
	{
		*pdst ++ = *pstr ++;
	}
	return dst;
}

void *sky_memecpy(void *dst, const void *str, int n)
{
	if (NULL == dst || NULL == str || n <= 0)
	{
		return NULL;
	}
	
	char *pdst = (char *)dst;
	char *pstr = (char *)str;
	if (pdst > pstr && pdst < pstr + n)
	{
		pdst = pdst + n - 1;
		pstr = pstr + n - 1;
		while (n --)
		{
			*pdst -- = *pstr --;
		}
	}
	else
	{
		while (n --)
		{
			*pdst ++ = *pstr ++;
		}
	}
	return dst;
}
int main()
{
	char str_1[100] = "heLlo,world";
	char str_2[100] = "heLlo,world";
	sky_memecpy_1(str_1+1,str_1,strlen(str_1));
	printf("%s\n",str_1);

	sky_memecpy(str_2+1,str_2,strlen(str_2));
	printf("%s\n",str_2);
    return 0;
}