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

技术2024-06-15 175

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, int size)

{ 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,int count){ char *pDest=static_cast<char *>(dest); const char *pSrc=static_cast<const char *>(src); if( pDest>pSrc && pDest<pSrc+count ) //判断临界区域，无重复则正向拷贝，重复则逆向拷贝 { for(int i=count-1; i<=0; i--) { pDest[i]=pSrc[i]; } } else { for(int i=0; i<count; i++) { pDest[i]=pSrc[i]; } } return pDest;}

void *Memmove(void *Dst, const void*Src,int 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,int 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++; } } else /*反向拷贝*/ { psrc += n; pdest += n; for(int i=0;i<n;i++) { *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;}

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------strcat void mycat(char *s1, char *s2) { while(*s1++); s1--; while(*s1++= *s2++); } ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------strcpy void mycpy(char *s1, char *s2) { while(*s1++= *s2++); } ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

strcmp int mycmp(char *s1,char *s2) { for(; *s == *t;s++,t++) if(*s== 0)

return0;

return *s - *t;

} ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------strlen int mylen(char *s1) { char*p = s1; while(*p++); returnp - s -1; }---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------strlwrchar* strlwr(char *s) { unsignedchar AL; registerchar *DX,*SI; DX=SI=s; while((AL=*SI++)!='/0') { AL-='A'; if(AL>'Z'-'A')

continue;

SI[-1]+='a'-'A'; } return DX;

}

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