strncmp实现

;***

;int strncmp(first, last, count) - compare first count chars of strings

;

;Purpose:

;       Compares two strings for lexical order.  The comparison stops

;       after: (1) a difference between the strings is found, (2) the end

;       of the strings is reached, or (3) count characters have been

;       compared.

;

;       Algorithm:

;       int

;       strncmp (first, last, count)

;             char *first, *last;

;             unsigned count;

;             {

;             if (!count)

;                     return(0);

;             while (--count && *first && *first == *last)

;                     {

;                     first++;

;                     last++;

;                     }

;             return(*first - *last);

;             }

;

;Entry:

;       char *first, *last - strings to compare

;       unsigned count - maximum number of characters to compare

;

;Exit:

;       returns <0 if first < last

;       returns 0 if first == last

;       returns >0 if first > last

;

;Uses:

;

;Exceptions:

;

;*******************************************************************************