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

void prepend(char* s,char ch){
    int len = strlen(s);
    memmove(s, s + 1, len - 1);
    s[len - 1] = '\x0';
}


void RemoveWhitespace(char* InStr, char ch){
     int n(0);

if (InStr == NULL){
    return;
}
else if ((*InStr) == '\x0'){
    return;
}   
else if ((*InStr) != ch){
    RemoveWhitespace(InStr + 1,ch);
}
else{
    while ((*InStr) == ch){
        prepend(InStr,InStr[0]);
        n++;
    }
    RemoveWhitespace(InStr + n,ch);
}
}