C: is there any benefit in using for(;;)?

Question

I found this implementation for char * strchr (const char *string, int c);:

for (;;) 
  if (*string == c)
    return (char *) string;
  else if (*string == '\0')
    return NULL;
  else
    string++;

For me, though, it would be equivalent to do the following, which would be way easier to read:

while (*string != c && *string != '\0')
  string++;

return (*string == c) ? ((char *) string) : (NULL);

I take it there is some reason for the libc to implement the first one. But any take on what's the reason behind it?

As a long-shot, it could be some way to make the code "easier" to optimize by localizing it a bit more, and re-using the same expression's result (`*string`) more closely to the last usage. — unwind, Apr 10 '13 at 09:28
If you're really want to know, put those two codes in a test project in separate functions, and compare the generated assembly code at different optimization levels. It might turn out their version optimizes better? — Some programmer dude, Apr 10 '13 at 09:29

score 6 · Answer 1 · answered Apr 10 '13 at 09:25

6

Yes, Visual Studio doesn't like while(1) when you bump up the warning level to the maximum (especially if you ask it to treat warnings as errors), but is OK with for(;;).

answered Apr 10 '13 at 09:25

Alexey Frunze

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what about while (true) ? – TheBlastOne Apr 10 '13 at 09:26
3

+1. For information, the Visual Studio warning is "conditional expression is constant" and also applies to `while (true)` – simonc Apr 10 '13 at 09:27
@TheBlastOne What kind of difference are you seeing between the two non-zero constants in this context? – Alexey Frunze Apr 10 '13 at 09:28
I don´t see any difference. I asked if there might be one. As simonc said, there is none. – TheBlastOne Apr 10 '13 at 09:30
@TheBlastOne I don't either. For the purpose of checking whether the conditional expression is 0 or not and whether it's constant or not they are identical. – Alexey Frunze Apr 10 '13 at 09:31

C: is there any benefit in using for(;;)?

1 Answers1