函数strcpy、strcat和strcmp实现源码

前两天在codeproject挖坟时找到的......

 

/*************************************************************************char *strcpy(dst, src) - copy one string over another**Purpose:* Copies the string src into the spot specified by* dest; assumes enough room.**Entry:* char * dst - string over which "src" is to be copied* const char * src - string to be copied over "dst"**Exit:* The address of "dst"**Exceptions:************************************************************************/char* strcpy(char * dst, const char * src){char * cp = dst;while( *cp++ = *src++ );/* Copy src over dst */return( dst );}/*************************************************************************char *strcat(dst, src) - concatenate (append) one string to another**Purpose:* Concatenates src onto the end of dest. Assumes enough* space in dest.**Entry:* char *dst - string to which "src" is to be appended* const char *src - string to be appended to the end of "dst"**Exit:* The address of "dst"**Exceptions:*************************************************************************/char* strcat ( char * dst , const char * src ){char * cp = dst;while( *cp )cp++;/* find end of dst */while( *cp++ = *src++ ) ;/* Copy src to end of dst */return( dst );/* return dst */}/*************************************************************************strcmp - compare two strings, returning less than, equal to, or greater than**Purpose:* STRCMP compares two strings and returns an integer* to indicate whether the first is less than the second, the two are* equal, or whether the first is greater than the second.** Comparison is done byte by byte on an UNSIGNED basis, which is to* say that Null (0) is less than any other character (1-255).**Entry:* const char * src - string for left-hand side of comparison* const char * dst - string for right-hand side of comparison**Exit:* returns -1 if src < dst* returns 0 if src == dst* returns +1 if src > dst**Exceptions:*************************************************************************/int strcmp ( const char* src, const char* dst ){int ret = 0 ;while( !(ret = *(unsigned char *)src - *(unsigned char *)dst) && *dst)++src, ++dst;if ( ret < 0 )ret = -1 ;else if ( ret > 0 )ret = 1 ;return( ret );}