How to use bit-fields in order to copy data into a struct from a binary?

Question

I have a binary file that I am trying to extract data from. The last 5 data points int the file are 10 bit integer types and I am struggling on how to extract that information and convert it into something readable. I have tried the following code:

struct bitField
{
    unsigned value: 10;
};

struct Data
{
    bitField x;
}

int main()
{
    std::array<char,696> buffer;
    std::ifstream file ("file.bin", std::ios::in | std::ios::binary);
    file.read(buffer.data(),buffer.size());

    Data a;

    std::memcpy(&a.x.value,&buffer[612],sizeof(struct bitField));

}

I am then met with the error attempt to take address of bit-field. I have then tried using std::bitset<10> in place of bitField in my Data struct. And while I do not get a compiler error, I get back a bunch of 0's instead which I believe is incorrect data.

How do you properly read in the data?

Answer 1

You can't take an address of a bit-field value as it may not be byte-aligned. You should copy directly into a.x (not a.x.value).

Further, you don't really need to have a separate bitfield struct. You can simply put bitfields right into Data struct.

See this on how to use bitfields: https://www.geeksforgeeks.org/bit-fields-c/