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 ); }