Someone

char *
strip_invalid_chars(char *string)
{
        char *c = string;
        char *c2 = string;
        char *last_non_space = NULL;
        /* c is source, c2 is target */
        for(; c && *c; c++)
                switch (*c)
                {
                case '\f':
                case '\n':
                        break;
                case ' ':
                        *c2++ = (*(c + 1) != ' ') ? *c : '\0';
                        break;
                default:
                        *c2++ = *c;
                        last_non_space = c2;
                        break;
                }
        *c2 = '\0';
        if(last_non_space)
                *last_non_space = '\0';
        return string;
}