Conditional operator syntax

Question

I have been reading C++ Primer for a whole day and stuck at this piece of code which I accidentally typed out:

int max = 5, min = 4;
max = (max > min) ? max : min;

It becomes so wired for me to think of it as max = max; .

According to my understanding the right side max becomes a rvalue so it is merely a value 5 . I'm not sure at all...

Anyone please explain it to me in plain words what's this syntax is?

As a newbie I think I'm not able to understand too complex answers.
Many thanks in advance!

Answer 1

There is nothing strange about the expression

max = max;

because there is no requirement the right hand side must be an rvalue, it just happens to be an rvalue often.

For example this is a typical copy from one lvalue to another

int x = 5;
int y;
y = x;

In this case x is not an rvalue, yet it appears on the right hand side. It is simply used to copy-assign to y .

So in your ternary expression either max = max or max = min are the two assignments that can possibly occur, and both are assignments using lvalues.

Answer 2

The expression:

max = (max > min) ? max : min;

could be decomposed to:

if (max > min) {
    max = max;
} else {
    max = min;
}

Thus, what is happens is max is compared to min and whichever is greater than the other gets assigned to max . The last operation, in the case where max is greater than min , is called self assignment:

max = max;

which is a perfectly legal operation, with accordance with the standard.