c strcmp source code

Question

int strcmp(const char *s1, const char *s2)

{
  int ret = 0;

  while (!(ret = *(unsigned char *) s1 - *(unsigned char *) s2) && *s2) ++s1, ++s2;

  if (ret < 0)

    ret = -1;
  else if (ret > 0)

    ret = 1 ;

  return ret;
}

I review the code from : http://www.jbox.dk/sanos/source/lib/string.c.html

I suppose that there're some problem. If strlen(s2)>strlen(s1),then ++s1 may beyond the range. Unfortunately, then the function return error.

One small problem I do see with the code in your link is that strcmp and strncmp returns the result differently. strcmp unnecessarily clamps the result to the -1..+1 range, while strncmp returns the full difference. — kusma
– kusma, Commented Dec 21, 2010 at 9:20

StasM · Accepted Answer · 2010-12-21 09:13:49Z

7

No, there's no such problem since the loop continues only while *s1 and *s2 are equal and *s2 is not 0. If s1 is shorter, once it gets to the \0 at the end of s1, the equality condition would break and the loop would stop.

answered Dec 21, 2010 at 9:13

StasM

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Simone · Accepted Answer · 2010-12-21 09:10:09Z

1

No, there's not such a problem, provided that s2 is '\0'-terminated.

answered Dec 21, 2010 at 9:10

Simone

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Comments

kusma · Accepted Answer · 2010-12-21 09:13:16Z

1

s1 is implicitly guarded due to zero-termination. The zero-termination will lead to there being a difference between "*(unsigned char ) s1" and "(unsigned char *) s2", terminating the loop.

So no, the code looks correct to me.

answered Dec 21, 2010 at 9:13

kusma

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