Thread: Conceptual ambiguity "function prototype"

Hi
I found some ambiguities about the concept "function prototype". MSDN tells me this:

Code:

A function declaration precedes the function definition and specifies the name, return type, storage class, and other attributes of a function. 
To be a prototype, the function declaration must also establish types and identifiers for the function's arguments.

Whereas many other sources tell this:

Code:

A function prototype is a declaration of a function that declares the types of its parameters.

So to be a function prototype, do "the identifiers for the function's arguments" need to be specified or not? Or just providing parameter types is enough to be a function prototype? I think this is also a problem of the choice of parameter-declaration:

Code:

parameter-declaration: 
declaration-specifiers declarator                           // named
declaration-specifiers abstract-declarator<opt>   // anonymous

Can the anonymous be used in a function prototype?

At last, what's necessary information for a function prototype if not? Now I think only parameter types are needed, right?

Thanks in advance!

You've missed one key thing, function prototype != function declaration. Those two quotes are not specifically discussing the same thing, although they're [very] similar.

> Or just providing parameter types is enough to be a function prototype?
Yes.

Originally Posted by password636

So can I think this way: a function declaration or definition which provides the parameter types is taken to be a function prototype by the compiler. The compiler then uses the prototype to check parameters for subsequent function calls.

Yes. The confusion in this area usually comes from the declaration/definition distinction. All definitions are also declarations, but not all declarations are definitions. A declaration which is not a definition is a prototype.

The purpose of prototypes is to indicate the specific calling signature for the function in question. This includes the parameter types, but in the case of member functions, also includes CV qualifiers (const and volatile) as applied to the function as a whole.

In C, prototypes are optional, although the compiler may warn if you forget them. If a prototype is given, it MUST match the definition which comes later on.

In C++, ALL functions must be declared at the point of use. A prototype or previous definition is sufficient.

Originally Posted by brewbuck

In C, prototypes are optional, although the compiler may warn if you forget them. If a prototype is given, it MUST match the definition which comes later on.

Only in C90, though. In C99, the implicit int and implicit function declarations are errors.
So it is GOOD practice to always use prototypes.