Get sizeof anonymous struct inside union

I’m hoping this isn’t a duplicate question, but I’ve searched in some detail and haven’t found my exact case before.

I have a simple struct that I also want to be able to access as a simple byte array

union
{
  struct
  {
    unsigned char a;
    unsigned char b;
    // ... Some other members ...
    unsigned char w;
  };
  unsigned char bytes[sizeof( what? )];
} myUnion;

Notice the struct is not named and it also isn’t given its own member name. This is so that I can use myUnion.a to access that member, and not myUnion.myStruct.a.

However, without some name, how can I get the size of the struct for myUnion.bytes[] other than manually calculating it each time I change something?

My current workaround is to use a #define to make up for the myUnion.myStruct problem, but that has the negative side-effect of ruining my auto-complete in the editor, and also makes my data structures harder to understand.

Any ideas?

Note: This is running on an 8-bit processor. There are no issues with word alignment and such. That said, any caveats should probably be stated so someone else doesn’t use a proposed solution inappropriately.

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