Why does this code produce a warning referring to the comma operator?

Question

When answering this question, I came across this code...

#include 

int main()
{
    int const income = 0;
    std::cout << \"I\'m sorr         


        

Answer 1

I think they just forgot to change the warning text

int main() {
   1, 2;
}

prog.cpp:2: warning: left-hand operand of comma has no effect
prog.cpp:2: warning: right-hand operand of comma has no effect

The expr, expr operator evaluates the left operand, then evaluates the right operand and yields the result of the right operand's evaluation. If the right operand has no effect and its value is not used, it's probably a bug in the program.

Now they just abused the above warning text to warn for other binary operators, it seems.

Answer 2

Your given program doesn't produce that warning for me with MSVC2010, it only produces

warning C4552: '<' : operator has no effect; expected operator with side-effect

As that should be a << before income;. (Note: Ideone doesn't produce a warning at all.)