I don't want to waste memory

[dubae524]

Hey everybody! I've got a question: You see, I only want to use 2 bits for a program. The first thing I did was create a 2-itemed bool array, but I couldn't print it out on the screen properly. So does anyone know how to just use a specific number of bits without having to waste the rest? Help would be greatly appreciated. Thanks!

[HarryW]

You can't only use 2 bits. The memory isn't addressed that way. The smallest variable you can use is a byte.

[dubae524]

Well, what about the bool type? That only uses one bit.

[HarryW]

It doesn't. Boolean variables are just typedefs for an integer type, and I have a feeling that's a 32 bit integer. zero is false and anything non-zero is true.

You can pack 32 bit flags into a 32-bit int if you want, but you can only access/modify those flags using bit-masking. The memory cannot be addressed in bits.

[CornedBee]

You can use a bitset container for bit flags, but it still allocates memory in blocks of 32 bits for faster access.

And to be serious: there isn't any difference between using 2 bits or 32 bits if you don't do it 2000 times. This is not the '60s. If you do it 2000 times - well then you don't need 2 bits, but 4000 bits .

[transcendental]

Bool is an enum type, I heard.

[CornedBee]

bool types:
BOOL is a typdef of windows = int. TRUE is a define for 1, FALSE is 0.
bool is a native C++ datatype. Size depends on the compiler, usually 32 bit. But a 64-bit gcc version first had a 64-bit bool, then changed it to 8 bit in a later release.
VARIANT_BOOL is again a typedef of windows to int. In that case, true is -1 (0xFFFFFFFF) and false is 0, as in VB.

I don't know about others.

[HarryW]

Originally posted by transcendental
Bool is an enum type, I heard.

Enums are still integers behind the scenes. You have to store the value somewhere, and in most cases that's in a 32-bit variable.

[parksie]

To extend, make no assumptions about the size of anything, except char (which I think is guaranteed to be 1, whether or not it actually takes up 1 byte or not )

[CornedBee]

Yep, char is guaranteed to be 1 minimum unit, 8 bits (1 byte) on a pc, but not necessarily on all computers.

At least I think so.

[parksie]

I'm not sure of implementation details (such as on systems where you don't have bits and bytes, or if a byte is 10 bits....... ) but I think sizeof(char) is defined in the standard to be "1".

Anyone got a copy of the standard? I *really* ought to buy myself one at some point

[CornedBee]

Yeah, if it wasn't that you have to pay I would have gotten the standard long ago.

[parksie]

If it would actually do any good, I'd have got a copy of the standard through work (for work purposes) on expenses, but somehow I doubt anyone round here is actually bothered about following standards and are quite happy to churn out incorrect code...........*sigh*