c - Is sscanf considered safe to use?

Question

I have vague memories of suggestions that sscanf was bad. I know it won't overflow buffers if I use the field width specifier, so is my memory just playing tricks with me?

Answer 1

I think it depends on how you're using it: If you're scanning for something like int, it's fine. If you're scanning for a string, it's not (unless there was a width field I'm forgetting?).

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Edit:

It's not always safe for scanning strings.

If your buffer size is a constant, then you can certainly specify it as something like %20s. But if it's not a constant, you need to specify it in the format string, and you'd need to do:

char format[80]; //Make sure this is big enough... kinda painful
sprintf(format, "%%%ds", cchBuffer - 1); //Don't miss the percent signs and - 1!
sscanf(format, input); //Good luck

which is possible but very easy to get wrong, like I did in my previous edit (forgot to take care of the null-terminator). You might even overflow the format string buffer.