merging bits

**Drac** · 12-21-2008

I have two arrays of UINT32's that look like this.

Code:

vector<UINT32> a;
vector<UINT32> b;

I'm using them to store bits. Here's my problem.

Let's imagine both a and b have 48 bits stored in them, so they both have size()==2. But only half of the second UINT32 is actually being used as bits. I need to insert b onto a, but I want to insert it on the bit level. So after the insertion is complete the result should be size()==3 and 96 bits total. The bits must also stay in the same order as they are in currently, so no swapping. The problem is that I have no idea how to do this, but it seems like there must be a way. If anybody needs clarification on anything just ask.

**m37h0d** · 12-21-2008

why would you want to thwart the idea of container classes by bypassing their access methods?

**Drac** · 12-21-2008

I believe I have actually found my solution in Guru Of The Week 72.
http://www.gotw.ca/gotw/072.htm

@m37h0d
The way I'm looking at it I need to. I'm only using vector for its memory management help. If I were to use vector<UINT32>::Insert to add b to a there would be 16 bits between left unused.

edit: It looks like I'm going to end up using vector<bool> or bitset though.
edit2: make that vector<bool>
edit3: make that dynamic_bitset

**m37h0d** · 12-21-2008

i'm sure laserlight, et al. will disagree, but to me it seems easier to use char * and do the memory management yourself imho.

**Elysia** · 12-21-2008

It is not. Especially not when vector<bool> does it all for you. You think like a C programmer. What are you doing here?

**anon** · 12-21-2008

Isn't vector<bool> deprecated?

dynamic_bitset (boost has one but is it going to make into C++0x?) seems like a good choice.

**m37h0d** · 12-21-2008

Originally Posted by Elysia

It is not. Especially not when vector<bool> does it all for you. You think like a C programmer. What are you doing here?

shrug.

**anon** · 12-21-2008

This seems to miss a lot of functionality that you'd expect from a bitset (most notably copy constructor and assignment operator). See here for what boost::dynamic_bitset has. Then think if you want to implement all that all over.

Your implementation also suffers from a number of problems, such as mixing realloc and delete[] (and using realloc in an unrecommended way - and reduplicating code that does reallocing). And what's with the C-style casts to T*. Any good coming if T happens to be something like std::string? And it isn't really a bitbuffer, as it appears to use one byte per bit.

**m37h0d** · 12-21-2008

yeah, true. it was more an example of how i thought the problem could be tackled much more simply than that GOTW page. but i shouldn't post things that aren't totally correct, especially if i'm not really interested in doing it correctly to a T (pun intended).

and despite my unfortunate naming, it wasn't necessarily a bitbuffer so much as it was directed at the OP's problem.

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