[kijin]

-1 can be useful, too, especially if you've already assigned a certain meaning to 0.

Javascript developers are used to certain functions returning -1 if there's no match, so -1 shouldn't feel strange as long as it's well documented.

[dorgo]

I wonder why they decided to use -1. Why not undefined or NaN or even null? The -1 produces bugs which go unnoticed for a long time.

[themulticaster]

On the other hand, there's strcmp()/strncmp(). I can never wrap my head around the fact that strcmp(s1, s2) == 0 (or even better, !strcmp(s1, s2)) means s1 is equal to s2.

[jeroenhd]

If you look at strcmp like "the difference when you compare the strings for sorting", it makes complete sense. If the first mismatch of strcmp(a, b) is smaller than 0, you put the a before b, otherwise you put b before a.

The fact that an equality check can be made by running a comparison function is useful, but that's not all the method does.

For other methods in much C code, a common mindset is that a method returning a value will return the error code, with error code details in errno. The error code for success is 0, which is fitting of course.

Had C implemented booleans, this problem would never have been a problem, because if(int) wouldn't have been a legal expression, but sadly booleans are implemented as integers in the language instead. I strongly dislike languages that do allow implicit casting from integers and such to a boolean, if(var!=0) is much more readable because of the explicit boolean expression.