Warning C4800: 'int' : forcing value to bool 'true' or 'false' (performance warning)

Question

I have this problem in my code:

bool CBase::isNumber()
{
return (id & MID_NUMBER);
}

bool CBase::isVar()
{
return (id & MID_VARIABLE);
}

bool CBase::isSymbol()
{
return (id & MID_SYMBOL);
}

Solution 1

FYI: Casts won't hide the warning by design.

Something like

return (id & MID_NUMBER) != 0;

should clearly state "I want to check whether this value is zero or not" and let the compiler be happy

Solution 2

Where's the declaration of id and MID_NUMBER? Are you sure they are not windef-style BOOLs rather than (lowercase) bool's? BOOL's have been in windef for decades typedef'd as an int; they pre-date proper C++ bool's and a lot of developers still use them.

Solution 3

Use the !! idiom eg

bool CBase::isNumber()
{
    return !!(id & MID_NUMBER);
}

Comments

[Admin]

Just to please the compiler !??

[deviantfan]

And why 2 ops instead of 1 (even if it is optimized)?

[deviantfan]

@Dieter Lücking: Non-standard workarounds are probably worse.

[Admin]

@deviantfan The warning itself is useless

[CreativeMind]

@DieterLucking: It can not be useless as it is warning.

[deviantfan]

@Lücking: Why? Of course the compiler can generate the correct stuff without changed code, but maybe the coder has not intended a implicit cast and finds a semantic error because of the warning?

[cup]

First inverts it so you get the inverse of what you actually wanted, second inverts that so you get what you actually wanted. Useful when you have a mix of BOOL (windows), Bool (xwindows) and bool (C++)

[ildjarn]

@deviantfan : The warning is not about semantics, it is about performance, which is specious.

[André Bergner]

I give you a +1. This was useful for me, since I have this warning in templated code where I cannot compare against 0 but !! works.