strcpy()、memcpy()、memmove()、memset()的实现

    技术2022-05-11  18

    strcpy(), 字符串拷贝.char *strcpy(char *strDest, const char *strSrc){    assert((strDest!=NULL) && (strSrc !=NULL));    char *address = strDest;        while( (*strDest++ = * strSrc++) != '/0')  NULL ;    return address ;      }

    memcpy, 拷贝不重叠的内存块 void *memcpy(void* pvTo, void* pvFrom, size_t size) //byte是java里的变量类型 {  assert(pvTo != NULL && pvFrom != NULL);  void* pbTo = (byte*)pvTo;  void* pbFrom = (byte*)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 *MemCopy(void *dest,const void *src,size_t count) {     char *pDest=static_cast<char *>(dest);     const char *pSrc=static_cast<const char *>(src);     if( pDest>pSrc && pDest<pSrc+count )     {         for(size_t i=count-1; i<=0; ++i)         {             pDest[i]=pSrc[i];         }     }     else     {         for(size_t i=0; i<count; ++i)         {    pDest[i]=pSrc[i];         }     }     return pDest; } void *Memmove(void *Dst, const void*Src,size_t count) {  assert(Dst && Src);  void* pDst = 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 pDst; } void* memmove(void *dest, const void *src,size_t n) {     if (n == 0) return 0;     if (dest == NULL) return 0;     if (src == NULL)    return 0;     char *psrc = (char*)src;     char *pdest = (char*)dest;     if((dest <= psrc) || (pdest >= psrc + n)) /*检查是否有重叠问题 */  {   for(int i=0; i < n; i++) /*正向拷贝*/   {    *pdest = *psrc;    psrc++;    pdest++;   }  }  else /*反向拷贝*/  {   psrc += n;   pdest += n;   for(int i=0;i<n;i++)   {             psrc--;             pdest--;             *pdest = *psrc;   }  }  return dest; } 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; }

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