Remove extra white spaces in C++

Question

I tried to write a script that removes extra white spaces but I didn\'t manage to finish it.

Basically I want to transform abc sssd g g sdg gg gf into

Answer 1

I have the sinking feeling that good ol' scanf will do (in fact, this is the C school equivalent to Anatoly's C++ solution):

void remove_extra_whitespaces(char* input, char* output)
{
    int srcOffs = 0, destOffs = 0, numRead = 0;

    while(sscanf(input + srcOffs, "%s%n", output + destOffs, &numRead) > 0)
    {
        srcOffs += numRead;
        destOffs += strlen(output + destOffs);
        output[destOffs++] = ' '; // overwrite 0, advance past that
    }
    output[destOffs > 0 ? destOffs-1 : 0] = '\0';
}

We exploit the fact that scanf has magical built-in space skipping capabilities. We then use the perhaps less known %n "conversion" specification which gives us the amount of chars consumed by scanf. This feature frequently comes in handy when reading from strings, like here. The bitter drop which makes this solution less-than-perfect is the strlen call on the output (there is no "how many bytes have I actually just written" conversion specifier, unfortunately).

Last not least use of scanf is easy here because sufficient memory is guaranteed to exist at output; if that were not the case, the code would become more complex due to buffering and overflow handling.