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I know that
someBool &= someOtherBool;

is equivalent to
someBool = someBool & someOtherBool;

The question is, are they equivalent to
someBool = someBool && someOtherBool;

? It seems to me that they should be, since bools are implemented as a single bit - right? It would make my code look a lot prettier.

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Noooo! Bools are not a single bit. Usually they're the same size as a char. The actual size may be implementation-specific, I'm not sure about that.

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Quote:
 Original post by Red AntNoooo! Bools are not a single bit. Usually they're the same size as a char. The actual size may be implementation-specific, I'm not sure about that.
That doesn't stop them only using a single bit. Whether they do or not, I'm not sure. *Starts hunting around in the C++ Standard*

EDIT: I couldn't find any guarantees about the storage of a bool; only that it is an integral type that you can do bitwise operations on. Still, I'd imagine that most compilers you tested it on would have both results equal.

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bools are not a single bit. I don't think it's defined how big they are actually. In VC2005 sizeof(bool) == 1.

Nevertheless using & instead of && *should* work since bools are guaranteed to convert to 0 or 1. I probably still wouldn't recommend it though.

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Cut it out with bitwise ops on bools. Here's why:

bool a, b, c; a = b & c;

What does this do? If you answered "ANDs b and c, and stores the result in a", you get no cookie. What it does: It generates an integer representation of b which is 1 if b is true and 0 if b is false. Then it generates an integer representation of c which is 1 if c is true and 0 if c is false. Then it takes the bitwise AND of the two integers. If the result is 0, a is assigned to be true. If the result is nonzero, a is assigned to be false.

So overall this happens to have the effect of logical AND. But don't use it like that, because that's not what's really happening.

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use &&

there is a reason we have boolean operators...

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Quote:
 Original post by TDragonThat doesn't stop them only using a single bit. Whether they do or not, I'm not sure. *Starts hunting around in the C++ Standard*

The sizeof bool cannot be smaller than the sizeof char. This is because types are required to be uniquely addressable, and char is defined as the smallest addressable type.

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Quote:
Original post by TDragon
Quote:
 Original post by Red AntNoooo! Bools are not a single bit. Usually they're the same size as a char. The actual size may be implementation-specific, I'm not sure about that.
That doesn't stop them only using a single bit. Whether they do or not, I'm not sure. *Starts hunting around in the C++ Standard*

Okay, let's look at the following example:

// The code below assumes that sizeof( bool ) == sizeof( unsigned char ).unsigned char nSomeChar = 8;unsigned char nSomeOtherChar = 2;bool bMyFirstBoolean& = *reinterpret_cast < bool* > ( &nSomeChar );bool bMySecondBoolean& = *reinterpret_cast < bool* > ( &nSomeOtherChar );// Bitwise AND of 8 and 2 ==> 0 ... which evaluates to false.bool bMyResultingBoolean = bMyFirstBoolean & bMySecondBoolean;// Logical AND of 8 and 2 (same as logical AND of true and true) ... evaluates to true.bool bTheTrueResult = bMyFirstBoolean && bMySecondBoolean;

Unless I've got a serious flaw in my thinking.

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OK, fair enough, I'll use logical and. :)

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This is something that you could easily test, and you should have before asking.
Now the question is, did you actually try and figure it out?

Now, on to the question.
Even though it's not something people would normally do, it does actually work.

If you use code and check EVERY possible way things could be, then it will work EVERY time. Now, in this case that proof is simple since bool only has two values, true and false.

So, do something like this:

void main(){	bool bFalse = false;	bool bTrue = true;	bool bTest1, bTest2, bTest3;	bTest1 = true;	bTest1 &= bTrue;	bTest2 = true;	bTest2 = bTest2 & bTrue;	bTest3 = true;	bTest3 = bTest3 && bTrue;	if( bTest1 == bTest2 && bTest1 == bTest3)		std::cout << "True" <<endl;	else		std::cout << "False" << endl;	bTest1 = false;	bTest1 &= bTrue;	bTest2 = false;	bTest2 = bTest2 & bTrue;	bTest3 = false;	bTest3 = bTest3 && bTrue;	if( bTest1 == bTest2 && bTest1 == bTest3)		std::cout << "True" <<endl;	else		std::cout << "False" << endl;	bTest1 = true;	bTest1 &= bFalse;	bTest2 = true;	bTest2 = bTest2 & bFalse;	bTest3 = true;	bTest3 = bTest3 && bFalse;	if( bTest1 == bTest2 && bTest1 == bTest3)		std::cout << "True" <<endl;	else		std::cout << "False" << endl;	bTest1 = false;	bTest1 &= bFalse;	bTest2 = false;	bTest2 = bTest2 & bFalse;	bTest3 = false;	bTest3 = bTest3 && bFalse;	if( bTest1 == bTest2 && bTest1 == bTest3)		std::cout << "True" <<endl;	else		std::cout << "False" << endl;}

And then everything comes out great, then you are good to go.
In this case the output I got was:

True
True
True
True

So, it works. There ya go. Next time you can try thiskind of method before asking. Otherwise, if you can't figure it out this way, come on back.

- Bnty_Hntr

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