如何判断整型越界

        if(isdigit(s[i])) {
            while(isdigit(s[i])) {
                int cur = s[i] - '0';
                if(ret < div || ret == div && cur < 8) {
                    ret = ret * 10 + (s[i] - '0');
                    i++;
                } else {
                    return flag == -1 ? INT_MIN : INT_MAX;
                }
            }
            break;
        }