[nandemo]

I keep seeing this argument on threads about interview questions.

The principle of not reinventing the wheel has nothing to do with interview questions. Sure, if you're actually working on solving an actual problem at your job, then most of the time you'll be better off using a standard library function instead of rolling your own.

In the context of the job interview, however, it doesn't matter if the solution to the problem is well-known or whether it can be found in a standard library. The problem of the interviewer is not to find out how to compare strings, it's determining if the candidate will be able to write proper code if hired. And the string-compare question might be a good starting point for evaluating the candidate's level. In any case, the fact that a solution is in a standard library is irrelevant.

If I was the interviewer I'd create a new data structure Foo and then ask the candidate to implement Foo.compare(). The question remains essentially the same, so I wonder what the candidate would reply.

[kragen]

> The problem of the interviewer is not to find out how to compare strings, it's determining if the candidate will be able to write proper code if hired.

The trouble with the question is that proper code to compare strings is almost certainly going to be a call to some existing library function. There are only rare cases (e.g. when you're one of the 50 people in the world who implement libc) that it makes sense to write it yourself. It's not clear from "code a string compare" exactly which set of wheels the interviewer wants reinvented: if strcmp is out of bounds, can you use strlen and memcmp? Because if strcmp was somehow buggy, that might be a reasonable thing to do. If the problem is that strcmp is too slow, should we maybe drop to assembly? Or change to a counted-string representation to avoid byte-by-byte operations? Or calculate hashes when strings are mutated, or intern them?

(Maybe in C strcmp is a bad example, since

    while (*s && *s == *t) { 
      s++; 
      t++;
    }
    return *t - *s;

is already about as simple as anything you'd do with strlen and memcmp...)

> If I was the interviewer I'd create a new data structure Foo and then ask the candidate to implement Foo.compare().

I think that's a better approach.

[epaga]

They would say Foo.ToString().Compare()... ;)

[skrebbel]

And not get the job, because it's likely wrong.