What is the size of bitset in C++

Question

I want to know how bitset actually allocates memory. I read from some blog that it takes up memory in bits. However when i run the following code:

   bitset<3> bits = 001;
   cout<<sizeof(bits);

I get the output as 4. What is the explanation behind it?

Also is there a method to allocate space in bits in C++?

Answer 1

You can approximate sizeof(bitset<N>) as:

1. If internal representation is 32bit (like unsigned on 32bit systems) as 4 * ((N + 31) / 32)
2. If internal representation is 64bit (like unsigned long on 64bit systems) as 8 * ((N + 63) / 64)

It seems that the first is true: 4 * ((3 + 31) / 32) is 4

Answer 2

I get the output as 4. What is the explanation behind it?

There is no information in standard about how bitset should be realized. It's implementation defined, look at bitset header of your compiler.

Also is there a method to allocate space in bits in C++?

No, there is no method to allocate space in bits in C++.