内存字符串memcpy,memmove,memset实现

之前的string.h我已经写过字符串的了.今天就谢谢mem的吧.

 

memcpy, 拷贝不重叠的内存块
void *memcpy(void* pvTo, void* pvFrom, size_t size)
{
assert(pvTo != NULL && pvFrom != NULL);
char* pbTo = (char*)pvTo;
char* pbFrom = (char*)pvFrom;
/* 内存块重叠吗？如果重叠，就使用memmove */
assert(pbTo>=pbFrom+size || pbFrom>=pbTo+size);
while(size-->0)
   *pbTo++ == *pbFrom++;
return pvTo;
}

void *Memmove(void *Dst, const void*Src,size_t count)
{
 assert(Dst && Src);
 char* pDst = (char*)Dst;
 

if (Dst (char*)Src + count)
 {
  while(count--)
   *Dst++ = *Src++;
 } 
else
{
   Dst = (char*)Dst + count - 1;
   Src = (char*)Src + count - 1;
   while(count--)
   {
      *Dst-- = *Src--;
   }
}
return pDst;
}

memset:把buffer所指内存区域的前count个字节设置成字符c

void * Memset(void* buffer, int c, int count)
{
char* pvTo=(char*)buffer;
assert(buffer != NULL);
while(count-->0)
*pvTo++=(char)c;
return buffer;
}