How to combine static_assert with sizeof and stringify?

Question

Memory usage is quite critical in my application. Therefore I have specific asserts that check for the memory size at compile time and give a static_assert if the size is d

Answer 1

Here's an alternative header-only solution if you can modify the struct's definition a bit and don't mind some ugliness.

template 
struct _MyStruct {
    static_assert(RealSize == ExpectedSize, "size is invalid");

    int x;
};

typedef _MyStruct), 4> MyStruct;

clang outputs:

prog.cpp:4:5: error: static_assert failed "size is invalid"
    static_assert(RealSize == ExpectedSize, "size is invalid");
    ^             ~~~~~~~~~~~~~~~~~~~~~~~~
prog.cpp:12:14: note: in instantiation of template class '_MyStruct<4, 8>' requested here
    MyStruct m;

One caveat here is that the check will only occur if you instantiate the type somewhere -- just using a pointer won't trigger the error, so definitely not a great fit for all situations!