void strtrim(char *str){
    char *begin = NULL, *end = NULL, *c;
    int at_space_substr = 1;
    for(c = str; *c; c++){
        if((*c == ' ' || *c == '\t') ^ at_space_substr){
            if(!begin)
                begin = c;
            else if(!at_space_substr)
                end = c;
            at_space_substr ^= 1;
        }
    }
    if(!begin)
        goto ret;
    if(!end)
        end = c;
    for(c = begin; c < end; c++, str++)
        *str = *c;
ret:
    *str = '\0';
}