一次两个字符串算法？

Question

Is there a way to do the following in a single command (in order to avoid the test)

if (mystring.find_first_not_of("X") != std::string::npos) {
    mystring.erase(0, mystring.find_first_not_of("X"));
}

Answer 1

mystring.erase(0, std::max(0, (std::make_signed<std::string::size_type>::type)
                           mystring.find_first_not_of('X')));

Or without C++11:

mystring.erase(0, std::max(0, (int)mystring.find_first_not_of('X')));