C++ POD struct inheritance? Are there any guarantees about the memory layout of derived members

Question

Let\'s say, I have a struct RGB and I want to create struct RGBA, which inherits RGB:

struct RGB {
    unsigned char r         


        

Answer 1

It's easy to check for padding: Print sizeof(RGB) and sizeof(RGBA). If it's not 3 respective 4 then the structures are padded, and you need to remove it.

As for if the member a comes after b, you can use offsetof to check each members offset. If the offset for a is one larger than the offset of b then a comes directly after b.