Xjyuk

I was solving a problem about bishop on a chessboard. At one point of my code, I included the following line:

std::cout << (abs(c2-c1) == abs(r2-r1)) ? 1 : 2 << std::endl;

This generates the following error:

error: invalid operands of types 'int' and '<unresolved overloaded function type>' to binary 'operator<<'

However, I instantaneously fixed this error by including an additional variable in my code:

int steps = (abs(c2-c1) == abs(r2-r1)) ? 1 : 2;
std::cout << steps << std::endl;

Now I have this question in my mind how the ternary operator works and how it's return type is determined (as the compiler called it <unresolved overloaded function type>).

This has nothing to do with how the return type is deduced and everything to do with operator precedence. When you have

std::cout << (abs(c2-c1) == abs(r2-r1)) ? 1 : 2 << std::endl;

it isn't

std::cout << ((abs(c2-c1) == abs(r2-r1)) ? 1 : 2) << std::endl;

because ?: has lower precedence than <<. That means what you actually have is

std::cout << (abs(c2-c1) == abs(r2-r1)) ? 1 : (2 << std::endl);

and this is why you get an error about a <unresolved overloaded function type>. Just use parentheses like

std::cout << ((abs(c2-c1) == abs(r2-r1)) ? 1 : 2) << std::endl;

and you'll be okay.

You have to put brackets around a ternary operation:

std::cout << ((abs(c2-c1) == abs(r2-r1)) ? 1 : 2) << std::endl;

If not the the << operator goes to the 2 and it gives an error because it doesn't have such overloaded function.

This happens because the bitwise left shift operator (<<) has a higher precedence than the ternary operator. You can see the full list of operators and its precedences in the following page of the C++ reference: https://en.cppreference.com/w/cpp/language/operator_precedence

The problem is caused by the

2 << std::endl;

part. Due to operatator precedence, that line is treated as:

std::cout << (abs(c2-c1) == abs(r2-r1)) ? 1 : (2 << std::endl);

Change it to

std::cout << ((abs(c2-c1) == abs(r2-r1)) ? 1 : 2) << std::endl;
// ^----------------------------------^
// Surrounding parenthesis