Terminology: Forward Declaration versus Function Prototype

Question

To me these terms are essentially synonymous when using the C programming language. In practice I might prefer "forward declaration" for in-file prototypes versus "function prototype" for prototypes included via a header file. But even that is an artificial distinction when you consider what happens after preprocessing. Perhaps I'm missing something.

Is there a consensus for when to use one term versus the other?

Answer 1

The term "prototype" refers to a specific declaration syntax; specifically, that the number and types of parameters to the function appear in the declaration. Given a function definition of

int foo(int a, char *b) {...}

you can have any of the following declarations:

int foo();                // a declaration, but not a prototype
int foo(a, b);            // a declaration, but not a prototype
int foo(int, char *);     // a declaration and a prototype
int foo(int a, char *b);  // a declaration and a prototype

Answer 2

IMO those are not really synonyms. To me "function prototype" refer to the function name and its parameters' and return's types. It does not only apply to what you call "forward declaration". All functions have a prototype.

We more often make a difference between a function declaration and its corresponding definition.