Removing trailing whitespaces of a string in c++ [duplicate]

I am trying to remove trailing whitespaces of a string in a concise/efficient way.

Let's say I have the string:

string input= "2 2 + " 

I used this in an attempt to make it input = "2 2+"

 std::string::iterator end_pos = std::remove(input.begin(), input.end(), ' '); input.erase(end_pos, input.end()); cout << input << endl; 

However, it removed all the whitespaces.

How would I implement it so it only removes trailing whitespaces?