Declaration and prototype difference

Question

What is the difference between declaration and prototype in C? In which situations they are called declarations and in which prototypes?

Answer 1

According to the C Standard (6.2.1 Scopes of identifiers)

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

That is a prototype provides the information about the types of the function parameters.

Consider for example

void f();

and

void f( void );

The first declaration is not a prototype because there is nothing known about the function parameters.

The second declaration is a prototype because it provides a type list of the function parameters (it is a special kind of the type list specifies that the function has no parameters).