Type of Function in C or C++

Question

I have a simple question:

What is the type of function in C or C++

As we can have pointers to function in C or C++, that means functions should have a specific type otherwise type checking during pointers to function creation have no meaning.

Can someone explain me, I am on the correct path or not?

If I am on the right path, How can I find the type of function?

Solution 1

Syntax for function pointers

The type of a function in C/C++ includes both the return type and the types of input parameters .

Consider the following function declaration:

int function(char, float);

A pointer to that function has the following type:

int (*funptr)(char, float); 

Similarly in general :

returntype function (argtype1, argtype2, argtype3)

A corresponding pointer to such a function is

returntype (*ptr) (atgtype1, atgtype2, atgtype3);  

There are be many different types of functions. Find a useful reference on function pointers here.

Also, this classification is based on the return type and argument types. Functions can also be classified on the basis of scope of their accessibility. like global functions, static functions etc. See here for a short introduction.

Solution 2

Of cause every function has it types,

for example, function

double foo(bar& f, const const baz*)

has a type of

function, that accepts reference to bar and constant pointer to baz and return double

It can be written like

double ()(bar&, const baz*)

A pointer to variable of types of that function will have type (variable that can store pointer to that function)

will have type

double (*)(bar&, const baz*)

Or, if you want to typedef pointer to functions of that type you can write

typedef double (*func_ptr)(bar&, const baz*)

Again,

func_ptr is a type of pointer to function, that accepts reference to bar and constant pointer to baz and return double

One thing here is that function decays to pointer to function, so you can write

func_ptr f = &foo;

and

func_ptr g = foo;

And it would be the same.

---

Now imagine, that you have

struct A
{
    double goo(bar& f, const const baz*);
};

Now goo has a type of

function of struct A, that accepts reference to bar and constant pointer to baz and return double

A pointer to this function will have type

double (A::*)(bar&, const baz*)

Note, that it types differs from type of free function foo. They are not compatible at all.

However, if goo were static function, the fact that it belongs to struct A would be insufficient (as far as member function requires implicit this argument and static function does not).

Solution 3

It's actually function signature which should match either with declaration or with function pointer

Function signature contains everything as such arguments type , no of arguments and return type.

Directly like variables you cannot say that particular function is of int type or float or char type or so on

Always remember it's signature as i said above.