Question

It’s interesting that using the function name as a function pointer is equivalent to applying the address-of operator to the function name!

Here’s the example.

typedef bool (*FunType)(int);
bool f(int);
int main() {
  FunType a = f;
  FunType b = &a; // Sure, here's an error.
  FunType c = &f; // This is not an error, though. 
                  // It's equivalent to the statement without "&".
                  // So we have c equals a.
  return 0;
}

Using the name is something we already know in array. But you can’t write something like

int a[2];
int * b = &a; // Error!

It seems not consistent with other parts of the language. What’s the rationale of this design?

This question explains the semantics of such behavior and why it works. But I’m interested in why the language was designed this way.

What’s more interesting is the function type can be implicitly converted to pointer to itself when using as a parameter, but will not be converted to a pointer to itself when using as a return type!

Example:

typedef bool FunctionType(int);
void g(FunctionType); // Implicitly converted to void g(FunctionType *).
FunctionType h(); // Error!
FunctionType * j(); // Return a function pointer to a function 
                    // that has the type of bool(int).

Answer 1

Since you specifically ask for the rationale of this behavior, here’s the closest thing I can find (from the ANSI C90 Rationale document – http://www.lysator.liu.se/c/rat/c3.html#3-3-2-2):

3.3.2.2 Function calls

Pointers to functions may be used either as (*pf)() or as pf().
The latter construct, not sanctioned in the Base Document, appears in
some present versions of C, is unambiguous, invalidates no old code,
and can be an important shorthand. The shorthand is useful for
packages that present only one external name, which designates a
structure full of pointers to object s and functions : member
functions can be called as graphics.open(file) instead of
(*graphics.open)(file). The treatment of function designators can
lead to some curious , but valid , syntactic forms . Given the
declarations :

int f ( ) , ( *pf ) ( ) ; 

then all of the following expressions are valid function calls :

( &f)(); f(); (*f)(); (**f)(); (***f)();
pf(); (*pf)(); (**pf)(); (***pf)();

The first expression on each line was discussed in the previous
paragraph . The second is conventional usage . All subsequent
expressions take advantage of the implicit conversion of a function
designator to a pointer value , in nearly all expression contexts .
The Committee saw no real harm in allowing these forms ; outlawing
forms like (*f)(), while still permitting *a (for int a[]),
simply seemed more trouble than it was worth .

Basically, the equivalence between function designators and function pointers was added to make using function pointers a little more convenient.