Logical OR operator result as rvalue

Question

This code I found while doing code review. Is there any hidden problem in this code or is it just fine?

myBool = myBoolA || ( oldState == AS_PLAYING );   //code #1

Edit: One typing mistake ( myBoolA in place of myBool ) by me created some nasty confusion; I am really sorry for that.

Actually the code to be reviewed is :

myBool = myBool || ( oldState == AS_PLAYING );   //code #1, not myBoolA

and my suggested code is:

if( oldState == AS_PLAYING ) myBool = true;   //code #2

Advantages with code#2 IMO :

1. better readability
2. if myBool is unintialized to begin with, there won't be Undefined behaviour.

Answer 1

myBool = myBoolA || ( oldState == AS_PLAYING ); is absolutely fine.

|| is a sequencing point in C++, so even if the expression on the right hand side depends on the left hand side (perhaps oldState is a reference to myBool or myBoolA ), the behaviour will be defined.

Your recommendation in changing this to

if( oldState == AS_PLAYING ) myBool = true;

is actually functionally different (the assignment to myBool is different for example), so don't change it to that.

Finally, note that the short-circuiting nature of || is obviated if || is overloaded. So always check that when refactoring code.

Answer 2

As per your comments later,

You can refactor as follows:

if(!myBool)
    myBool =  (oldState == AS_PLAYING);

this will save one extra assignment operation. when myBool is true before if

Answer 3

myBool = myBoolA || ( oldState == AS_PLAYING ); //code #1 seems to be correct version.

Your version is not equivalent to this. How? See

if myBoolA is true and ( oldState == AS_PLAYING ) is false. myBool will still be true, but in your version, it will not be set.

After EDIT

if( oldState != AS_PLAYING )  myBool = false;    //code #2 more readable IMO

This will be fine only if, myBool is initialized with true .