What is &= and |=

Question

I was going through some VC++ code in a large code-base and came across this:

    if (nState & TOOL_TIPS_VISIBLE)
        nState &= ~TOOL_TIPS_VISI         


        

Answer 1

What hasn't been mentioned is that both &= and |= operators can be overloaded. Therefore, the code you posted depends on the type of nState (although it's quite clearly an int, so most probably this doesn't apply here). Overloading &= does not implicitly overload &, so in this case

x &= y might not be the same as x = x & y

It might also depend on what TOOL_TIPS_VISIBLE is.

struct s{
   int x;
};

void operator &= (int& x, s y)
{
   x = 0;
}

Now whenever you do:

s TOOL_TIPS_VISIBLE;
x &= TOOL_TIPS_VISIBLE;

x will become 0. Again, highly unlikely, but good to know nevertheless.

All other answer probably apply here, but this is worth considering.