memcpy，memset，memmove的使用与实现

void *memcpy( void *dest, const void *src, size_t count );

返回值：

memcpy returns the value of dest.

参数：

dest

New buffer

src

Buffer to copy from

count

Number of characters to copy

Remarks

The memcpy function copies count bytes of src to dest. If the source and destination overlap, this function does not ensure that the original source bytes in the overlapping region are copied before being overwritten. Use memmove to handle overlapping regions.

实现：

void *my_memcpy(void *dst, const void *src, size_t count)
{
	void *ret = dst;
	char *pDst = (char *)dst;
	char *pSrc = (char *)src;
	while (count--) {
		*pDst++ = *pSrc++;
	}
	return ret;
}
           

void *memset( void * dest , int c , size_t count );

返回值：

memset returns the value of dest.

参数：

dest

Pointer to destination

c

Character to set

count

Number of characters

Remarks

The memset function sets the first count bytes of dest to the character c.

实现：

void *my_memset(void *dst, int val, size_t count)
{
	void *ret = dst;
	char *pDst = (char *)dst;
	while (count--) {
		*pDst++ = (char)val;
	}
	return ret;
}
           

void *memmove( void *dest, const void *src, size_t count );

返回值：

memmove returns the value of dest.

参数：

dest

Destination object

src

Source object

count

Number of bytes of characters to copy

Remarks

The memmove function copies count bytes of characters from src to dest. If some regions of the source area and the destination overlap, memmove ensures that the original source bytes in the overlapping region are copied before being overwritten.

实现：

void *my_memmove(void *dst, const void *src, int count)
{
	void *ret = dst;
	char *pDst = (char *)dst;
	char *pSrc = (char *)src;
	if (pDst > pSrc || pDst < pSrc + count) {
		while (count--) {
			*(pDst + count - 1) = *(pSrc + count - 1);
		}
	}
	else {
		while (count--) {
			*pDst++ = *pSrc++;
		}
	}
	return ret;
}