Question

Possible Duplicate:
function call with different semantics

I am reading about function pointers in C. I tried this program:

#include <stdio.h>

int foo(void)
{
    printf("At foo.");
    return 0;
}

int main (void)
{
    printf("%p\t%p\t%p\n", &foo, foo, *foo);
    return 0;
}

The output for this program is:

0040138C    0040138C    0040138C

In 1-D array <datatype> <identifier>[N], identifier and &identifier points to the same value but the nature of the values are different. One is of type datatype* and the other is of type pointer to the 1-D array. Analogously, for functions, the foo and &foo are the same. But what about *foo and what is the nature of &foo, foo, *foo?

Answer 1

A plain foo is already a function pointer:

6.3.2.1 – 4

A function designator is an expression that has function type.
Except when it is the operand of the sizeof operator or the unary
& operator, a function designator with type ‘‘function returning
type’’ is converted to an expression that has type ‘‘pointer to
function returning type’’.

You may obtain the address of a function using &, which yields a pointer to function ...:

6.5.3.1 – 1-3

The operand of the unary & operator shall be either a function
designator… The unary & operator yields the address of its operand.
If the operand has type ‘‘type’’,
the result has type ‘‘pointer to type’’

It’s legal to apply the indirection operator to a function designator:

6.5.3.2 – 3

The unary * operator denotes indirection. If the operand points to a
function, the result is a function designator

tldr:

So there you have it. They all do the same thing.

---

EDIT

What is ‘function type` in C

Quick! To the standard!

6.2.5 – 1

Types are partitioned into object types (types that describe
objects) and function types (types that describe functions).

6.2.5 – 20

A function type describes a function with specified return type. A
function type is characterized by its return type and the
number and types of its parameters. A function type is said to be
derived from its return type, and if its return type is T, the
function type is sometimes called ‘‘function returning T’’. The
construction of a function type from a return type is called
‘‘function type derivation’’