Find holes in C structs due to alignment

Question

Is there a way in gcc or clang (or any other compiler) to spit information about whether a struct has holes (memory alignment - wise) in it ?

Thank you.

ps: If

Answer 1

You can detect such "holes" via the offsetof macro:

#include 

struct test {
  char a;
  int b;
};
...
printf("%zu", offsetof(struct test, b));

If this prints more than 1, b obviously has alignment requirements and the compiler produces a gap in between.

Obviously this happens at runtime, not at compile-time, but you can write a script that produces a similar source file, compiles and runs it before the rest of your project, and then, based on the output you do further decisions on how to build your project.

I don't think any compiler provides a facility to notify you about that.