memcpy和strlen函数的实现

#include <stdio.h>
#include <stdlib.h>			//malloc()函数
typedef unsigned int size_t;

size_t my_strlen(const char * str)
{
	const char *sc = NULL;
	if(str == NULL)
		return 0;
	for(sc = str;*sc != '\0';sc++)
	{
		/*  do nothing */
	}
	return sc - str;
}

void * my_memcpy(void *pDst,const void *pSrc,size_t len)
{
	if((pDst == NULL)&&(pSrc == NULL))	//判断指针是否为空
		return NULL;
	char *tmp = (char *)pDst;
	char *s = (char *)pSrc;

	while(len--)
		*tmp++ = *s++;
	return pDst;
}

int main()
{
	char *src = "hello world";
	int count = my_strlen(src);
	printf("count = %d\n",count);
	char *dst = (char *)malloc(count + 1);	//申请空间

	my_memcpy(dst,src,count);
	*(dst+count) = '\0';
	printf("%s\n",dst);
    return 0;
}

执行结果：