In C, what is the difference between `&function` and `function` when passed as arguments?

Question

For example:

#include 

typedef void (* proto_1)();
typedef void proto_2();

void my_function(int j){
    printf(\"hello from function. I got          


        

Answer 1

There is no difference. For evidence see the C99 specification (section 6.7.5.3.8).

"A declaration of a parameter as ‘‘function returning type’’ shall be adjusted to ‘‘pointer to function returning type’’, as in 6.3.2.1."

Answer 2

There is no difference between &function and function - they're both addresses. You can see this by printing them both:

function bar(); 

.... 
printf("addr bar is 0x%d\n", &bar);
printf("bar is 0x%d\n", bar);

Answer 3

The difference is only stylistic. You have the same scenario when using function pointers:

void func (void);

...

void(*func_ptr)(void) = func;

func_ptr();    // call func
(*func_ptr)(); // call func

printf("%d\n", ptr); 
printf("%d\n", *ptr);

There are some who say that the (*func_ptr)() syntax is to prefer, to make it clear that the function call is done through a function pointer. Others believe that the style with the * is clearer.

As usual, there are likely no scientific studies proving that either form is better than the other, so just pick one style and stick to it.

Answer 4

there is no difference between &function and function when passing as arguement

however there is a difference between your typedefs. I do not know the official explanation, i.e what exactly the difference, but from what i remember

typedef void (*name1)(void);

and

typedef void(name2)(void);

are different:

name1 is a pointer to a function that takes no paramter and returns nothing

name2 is a function that takes no paramter and returns nothing

you can test it by compiling:

typedef void (*pointer)(void);
typedef void (function)(void);

void foo(void){}

int main()
{
    pointer p;
    function f;

    p = foo; //compiles
    p();

    f = foo; //does not compile
    f();
}

again, i am not the right person to explain exact reason of this behavior but i believe if you take a look at standards you will find the explanation somewhere there