In some Chinese C++ textbooks (For example: Tan Haoqiang C programming), there are often exercises like the following:

#include <iostream>

int main(){
    int i = 1;
    std::cout << (i++)+(++i) << endl;
}

The textbook provides the answer as 6, but when compiled with G++, the output is 4 or 5 or 6(Depends on level of optimization).

I want to have some specification for this operation, such as:In the same row, if the variable has been increment more than once, the value before the first increment of the variable is used as the reference value.

Thanks.