Question

My problem is, that I need to load a binary file and work with single bits from the file. After that I need to save it out as bytes of course.

My main problem is – what datatype to choose to work in – char or long int? Can I somehow work with chars?

Answer 1

Before beginning to code any thing make sure you understand endianess, c++ type sizes, and how strange they might be.

The unsigned char is the only type that is a fixed size (natural byte of the machine, normally 8 bits). So if you design for portability that is a safe bet. But it isn’t hard to just use the unsigned int or even a long long to speed up the process and use size_of to find out how many bits you are getting in each read, although the code gets more complex that way.

You should know that for true portability none of the internal types of c++ is fixed. An unsigned char might have 9 bits, and the int might be as small as in the range of 0 to 65535, as noted in this and this answer

Another alternative, as user1200129 suggests, is to use the boost integer library to reduce all these uncertainties. This is if you have boost available on your platform. Although if going for external libraries there are many serializing libraries to choose from.

But first and foremost before even start optimizing, make something simple that work. Then you can start profiling when you start experiencing timing issues.