1

Let's say I have a struct using bit-fields like that :

struct SomeData
{
  char someChar:5;
  char someSmallerChar:3;
}

The size of the content of one SomeData should be one char long instead of two, thanks to bitfields.

Now if I want to organize my data this way...

class SomeDataContainer
{
  std::vector<char> someChar;
  std::vector<char> someSmallerChar;
}

... I lose the benefit I had with the bit-fields regarding space efficiency. The size of the equivalent container is now twice the original one.

Is there a way to create a vector of char:5 and char:3 or something similar to it to get the same benefits while having the data in this vector format (contiguous in memory) ?

Improve this question
19
  • std::vector<SomeData> doesn't fit your needs because continuity, right? Commented Jul 15, 2019 at 13:06
  • Yes, I need someChar's to be contiguous and std::vector<SomeData> would put someSmallerChar's in the middle. Commented Jul 15, 2019 at 13:07
  • 1
    Of course there is a way: you just have to implement your own container that implements this functionality. There's nothing like this in the standard C++ library, but you can always write your own, and if it complies sufficiently with C++ library's container requirements, it should be usable with the rest of the library (algorithms, etc...) Commented Jul 15, 2019 at 13:08
  • 1
    There is std::vector<bool> which has bit-level granularity (and std::bitset with a compile-time length). The next higher granularity provided by the standard library is std::vector<char> (or similar). You could write your own container that allows granularity at the level you need. Commented Jul 15, 2019 at 13:09
  • 1
    @max The std::vector<bool> disaster is solely because it is a specialization, and not a completely different container Commented Jul 15, 2019 at 13:12
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