function - Should C declarations match definition including keywords and qualifiers such as "static", "inline", etc

Question

Consider this example of a function declaration and definition (in the same translation unit):

inline static int foo(int x);

...

int foo(int x)
{
  return x+1;
}

I know that the types need to match, but what about other keywords and qualifiers? Should inline static be in both cases? Or just the declaration?

And which part of the C standard or which coding guideline could I use to justify the answer?

Answer 1

No, for inline in particular, these should not be the same.

But the example is wrong from the start. For inline you need a definition (the whole function) with the inline in the .h file. By that, the inline, you avoid that the symbol is defined in several translation unit (.c) where you include the .h header.

Then, in exactly one translation unit you pout just the declaration without inline to indicate that the symbol should be generated in the corresponding .o object file.