一直想知道 strcpy()、memcpy()、memmove()、memset()的内部实现
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; }