something i bet you didnt know you could do with pointers.

[avansc]

pointers to functions are very powerful.
you can pass a function as a parameter- this is probably one of the coolest things you can to with any programming language

Code: Select all

#include <stdio.h>
#include <stdlib.h>

int add(int x, int y);
int sub(int x, int y);
int calc(int x, int y, int(*func)(int, int));

int add(int x, int y)
{
	return x+y;
}

int sub(int x, int y)
{
	return x-y;
}

int calc(int x, int y, int(*func)(int, int))
{
	return func(x, y);
}

int main(void)
{

	int (*fp1)(int, int) = add;
	int (*fp2)(int, int) = sub;

	printf("add via function poiter : %d\n", calc(2,1,fp1));
	printf("sub via function poiter : %d\n", calc(2,1,fp2));
	getchar();
	return 0;
}

[Falco Girgis]

Yeah, that is so badass. It's also straight C without any C++icism.

[M_D_K]

Used them manys a time.

I had them in an old version of a quake style in-game console.

[trufun202]

Those are known as Delegates in the C# world. They're great for asynchronous callbacks.

Delegates were actually the basis for my idea for the menu-driven conversations in my game. Except it's Lua, so I just passed a string of the function name, rather than a pointer.

[MarauderIIC]

Or, if you need flexibility when it comes to the parameters, you could use a functionoid
http://en.wikipedia.org/wiki/Functionoid

[avansc]

Or, if you need flexibility when it comes to the parameters, you could use a functionoid
http://en.wikipedia.org/wiki/Functionoid

a functionoid is just another name for a function.

function =
proc
procedure
method
functor
functionoid

that wiki page does not really have any usefull info on it.

[MarauderIIC]

Well, sort of. Quick illustration in C++ (to do the same thing in C, I think you have to use macros?)

Code: Select all

class Functionoid {
public:
    int sharedparam;
    virtual bool operator()() = 0;
};

class Fn1 : public Functionoid {
public
    int param1;
    int param2;
    virtual bool operator()();
};

class Fn2 : public Functionoid {
public:
    char param3;
    char param4;
    virtual bool operator()();
};

Code: Select all

main() {
    Fn1 fn1;
    fn1.param1 = fn1.param2 = fn1.sharedparam = 1;
    Fn2 fn2;
    fn2.param3 = fn2.param4 ='a';
    fn2.sharedparam = 2;
    doStuff(fn1);
    doStuff(fn2);
}
void doStuff(Functionoid& fn) {
    fn();
}

Effectively use a fn as a parameter but the fns you use don't have to have the same parameters.

[avansc]

Well, sort of. Quick illustration-

Code: Select all

class Functionoid {
public:
    int sharedparam;
    virtual bool operator()() = 0;
};

class Fn1 : public Functionoid {
public
    int param1;
    int param2;
    virtual bool operator()();
};

class Fn2 : public Functionoid {
public:
    char param3;
    char param4;
    virtual bool operator()();
};

Code: Select all

main() {
    Fn1 fn1;
    fn1.param1 = fn1.param2 = fn1.sharedparam = 1;
    Fn2 fn2;
    fn2.param3 = fn2.param4 ='a';
    fn2.sharedparam = 2;
    doStuff(fn1);
    doStuff(fn2);
}
void doStuff(Functionoid& fn) {
    fn();
}

i see, but thats not strickly a function. its a class.

[MarauderIIC]

Effectively acts as a function (another name for functionoid is function object). :)
Edited that a few times ^

[MarauderIIC]

Also it's the only way, that I know of, to do such a thing: pass functions as parameters, where the functions themselves don't have to have the same parameter types.

[avansc]

Also it's the only way, that I know of, to do such a thing: pass functions as parameters, where the functions themselves don't have to have the same parameter types.

no you can do that with out making a class for it

[MarauderIIC]

Besides C-macros, which I mentioned in the first post but forgot to mention in the other one, how?

[avansc]

Besides C-macros, which I mentioned in the first post but forgot to mention in the other one, how?

"pass functions as parameters, where the functions themselves don't have to have the same parameter types."

rephrase that a bit so i understand so i dont make a fool out of my self

[MarauderIIC]

Sure.

int calc(int x, int y, int(*func)(int, int));

You're stuck passing something that takes two ints.

Code: Select all

bool do(Functionoid& fn) { //or Functionoid* if you want
   return fn();
}

You're not stuck passing something that takes two ints.

Main:

Click here to see the hidden message (It might contain spoilers)

int main() {
Fn1 fn1;
fn1.param1 = 1;
fn1.param2 = 2;
fn1.sharedparam = 3;
Fn2 fn2;
fn2.sharedparam = 3;
fn2.param3 = 'a';
fn2.param4 = 'b';
do(fn1);
do(fn2);
}[/code]

See, I'm passing a function (object) as a parameter but the function (objects) don't have to have the same parameter types. One's parameters are ints, one's parameters are chars. Could do strings or something that can't be cast to an int, of course.

And pasted from my last post, the class details:

Click here to see the hidden message (It might contain spoilers)

Code: Select all

class Functionoid {
public:
    int sharedparam;
    virtual bool operator()() = 0;
};

class Fn1 : public Functionoid {
public
    int param1;
    int param2;
    virtual bool operator()();
};

class Fn2 : public Functionoid {
public:
    char param3;
    char param4;
    virtual bool operator()();
};

Alternatively you could probably add parameters to the () operator or one of the constructors; this is just a simple example though.

[bugmenot]

@MarauderIIC: That is not a functor as the parameters are stored before the functor is given to code that is invoking the function. This article should explain the uses of a functor: http://elysianshadows.com/phpBB3/viewto ... art=999999

Edit: Wrong url: http://en.wikipedia.org/wiki/Function_object