Strip whitespace from a string in-place?

Question

I saw this in a \"list of interview questions\". Got me wondering.

Not limited to whitespace necessarily, of course, easily generalized to \"removing some specific char

Answer 1

C doesn't have default arguments, and if you're programming in C++ you should use std::string and remove_if from .

You definitely can make this more efficient, by eliminating the calls to strlen, which are turning an O(N) algorithm into an O(N²) algorithm, and are totally unnecessary -- you're scanning the string anyway, so just look for the NUL yourself.

You can also make this more C-idiomatic, by using two pointers instead of array indexing. I'd do it like this:

void strip_char(char *str, char strip)
{
    char *p, *q;
    for (q = p = str; *p; p++)
        if (*p != strip)
            *q++ = *p;
    *q = '\0';
}