memcmp.c

来自「Many C samples. It is a good sample for 」· C语言 代码 · 共 34 行

/*  File   : memcmp.c
    Author : Richard A. O'Keefe.
    Updated: 25 May 1984
    Defines: memcmp()

    memcmp(lhs, rhs, len)
    compares the two memory areas lhs[0..len-1]  ??  rhs[0..len-1].   It
    returns  an integer less than, equal to, or greater than 0 according
    as lhs[-] is lexicographically less than, equal to, or greater  than
    rhs[-].  Note  that this is not at all the same as bcmp, which tells
    you *where* the difference is but not what.

    Note:  suppose we have int x, y;  then memcmp(&x, &y, sizeof x) need
    not bear any relation to x-y.  This is because byte order is machine
    dependent, and also, some machines have integer representations that
    are shorter than a machine word and two equal  integers  might  have
    different  values  in the spare bits.  On a ones complement machine,
    -0 == 0, but the bit patterns are different.

    This could have a Vax assembly code version, but as the return value
    is not the value left behind by  the  cmpc3  instruction  I  haven't
    bothered.
*/

int memcmp(lhs, rhs, len)
    register char *lhs, *rhs;
    register int len;
    {
	while (--len >= 0)
	    if (*lhs++ != *rhs++) return lhs[-1]-rhs[-1];
	return 0;
    }