I want to make a bitset in C++. I did a bit of research. All examples I found where like this:
bitset<6> myBitset;
// do something with it
But I don't know the size of the bitset when I define the variable in my class:
#include <bitset>
class Test
{
public:
std::bitset *myBitset;
}
This won't compile...
And initializing like this also doesn't work:
int size = getDependentSizeForBitset();
myBitset = new bitset<size>();
What you are saying at the beginning is not true. The "examples you found" did not look as you posted. It is impossible to use a non-constant value to parametrize a template. So, your first example is invalid. Only constant expressions can serve as non-type arguments for a template. I.e. the non-type argument has to be a compile-time constant.
Of looks like you want to create a bitset whose size is not a compile-time constant. In this case the
bitset
template is out of question. You need an implementation of run-time sized bitset. For example, you can usestd::vector<bool>
- in many (if not all) implementations this template is specialized to implement a packed array of boolean values, where each element occupies one bit (as opposed to anbool
object).You should check out boosts dynamic_bitset.
Use Boost::dynamic_bitset
Boost has a
dynamic_bitset
you can use.Alternatively, you can use a
vector<bool>
, which (unfortunately) is specialized to act as a bitset. This causes a lot of confusion, and in general is considered a bad idea. But that's how it works, so if that's what you need, you might as well use it, I suppose.bitset requires size as a template parameter, meaning the size has to be capable of being determined at compile-time. It cannot be based on a runtime condition, like user input.
For that, you should look into std::vector or boost::dynamic_bitset. std::vector is a specialized template instantiation that uses one bit per element. Unlike bitset, it can be dynamically sized.