Accessing bit level in C++

DataProtocol · 2004-01-23T16:59:06

I can''t seem to find any way of accessing the bit level of variables. Say I made a 2D map of tiles, each tile needs to have 1-8+ bools for certain flags. If I just use a bool, I''ll be using 8 bytes of memory to store the flags for each tile. However if I just treat a char as eight bools, and use it''s bits as my flag, then I would only use 1 byte of memory. Looking at large 255x255 maps, with several maps all that need to be in memory constantly, this would save a lot of memory. Problem is, I need to be able to access these bits fast (as fast as possible). Does anyone know how I could accomplish this?

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Started by DataProtocol January 23, 2004 12:30 PM

11 comments, last by DataProtocol 20 years, 2 months ago

Agony

3,452

January 23, 2004 04:14 PM

quote:Original post by Leffe That would be 32 bytes, bools are as large as integers, 4 bytes.

Not on all compilers and platforms. VC6''s bool is only 1 byte. (I just checked with a test program to make sure). The #defined BOOL used in many Windows programs, however, is 4 bytes.

"We should have a great fewer disputes in the world if words were taken for what they are, the signs of our ideas only, and not for things themselves." - John Locke

rypyr

252

January 23, 2004 04:17 PM

oh gad, don''t you people have anything better to do than nitpick each others comments?

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glassJAw

128

January 23, 2004 04:58 PM

DataProtocol:
If you really need to save memory, you could look into some simple compression techniques. Just decompress the maps as you need them.

If that's no good, vector<bool> (as suggested by Jingo) is a good alternative. In most implementations, a vector of booleans is actually a stored as a bitstring in memory.

Failing that, you're stuck with the bitwise and/or operators.

quote:Original post by rypyr
oh gad, don't you people have anything better to do than nitpick each others comments?

One could ask you the same question

[edited by - glassJAw on January 23, 2004 5:59:06 PM]

Accessing bit level in C++

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Accessing bit level in C++

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