what is the difference between function declaration and signature?

Question

In C or C++ what is the difference between function declaration and function signature?

I know something of function declaration but function signature is totally ne

Answer 1

The function signature doesn't include the return type or linkage type of the function.

OK, Wikipedia disagrees with me on the return type being included. However I know that the return type is not used by the compiler when deciding if a function call matches the signature. This previous StackOverflow question appears to agree: Is the return type part of the function signature?