Static function?

[rever]

Hi all!

I want to define a method which can be used by all the classes in my solution, like a global variable but a "global method". I have been reading and the closest concept I found was Static function. Is it the proper solution to what I am looking for? Is there anything better?

And just for the sake of curiosity: why everyone calls it static function?? Shouldn't it be static method since we are in a object-oriented language?

Thanks in advanced!

[Bazzy]

A static function is what you are looking for.
Often 'function' and 'method' are used to mean the same thing.

[moorecm]

In my opinion "member function" is the same as "method". (Not everyone in the engineering community agrees on the use of "method".)

[rever]

Ok thank you but I am getting some problems compiling. Specifically I am getting a: error LNK2019... it says something about external symbol which cannot be resolved.

I defined the static method in class Frame:

static void hello(){
	cout<<"Hello";
}

and then in a different class I write:

Frame::hello();

When i compile I get that ugly error :(.

Can anyone help please??

Thanks

[Richard101]

Static function: Is a function, but defined as a method, but this is what you wanna use..

[filipe]

since we are in a object-oriented language

What? C++ is not an OO language. It supports OOP.

[D80DSL3A]

Did you #include "Frame.h" in the other class? You may need to.

[Richard101]

Isn't Frame.h another math function? If it is you know all you have to do is

#include <cmath>

[Bazzy]

@rever
Can you replicate your situation? where/how did you declare/define/call that function?
@Richard101
WTF?

[sadavied]

Also, this may be not-so-obvious, where you defined the 'hello()' function you may need to write it this way:

std::cout << "Hello";

That is unless you did a 'using namespace std;' Without seeing the specific error I'm just guessing and thinking of what I can.

[rever]

Hi!

Sorry for answering so late!! Thank you all for the replies but I still have the problem.

I think I have defined correctly the static function:

static void hello(){
	cout<<"Hello";
}

because as long as I don't use it anywhere the compiler says nothing.

When I type it somewhere in my code (yes, Frame.h is included and it is not a math function):

Frame::hello();

I get that error in the compiler:

error LNK2019:  unresolved external symbol "public: static void __cdecl Frame::hello(void)" (?hello@Frame@@SAXXZ)...

I finally gave up and did it without a static function but now I am curious about where was the error. BTW, thanks again.

[Bazzy]

Can you explain more your situation? source-header files / inlined functions etc

[Richard101]

@Bazzy What do you mean?

[Bazzy]

Frame.h is a file, not a math function

[Mathhead200]

I get a link error when I declare a function, but don't define it... Then try to use it.

class Frame {
 public:
  static void hello(); //declaration, but not a definition (see the ;)
};

Try:

//tell the compiler that hello is a member of Frame
// (note that you only need the keyword "static" when declaring the function)
void Frame::hello() {
  cout << "Hello";
}

FYI: you can create a global function that doesn't belong to a class.
It would be smart to put it in a namespace though...

#include <iostream>

namespace my_space {
  using std::cout;
  
  //hello is now a global function and a member of my_space, full name is my_space::hello
  void hello() {
    cout << "Hello";
  }
}


using namespace my_space;

int main() {
  hello();
  return 0;
}

[rever]

Yes, I found where the mistake was, thanks Mathhead200! I was using the word static in both the definition and the declaration!!

Now it works properly :) (I keep the namespace option in my mind, but first I need to completely understand the concept of namespace)

[Mathhead200]

No problem. I'm glad it worked.

A namespace is just a way to avoid name conflicts (i.e. be able to have more then one variable named the same thing)
Example:

namespace A {
	int n; //because n is defined in namespace A its full name is A::n
	double x; //same here, A::x
}

namespace B  {
	int n; //you can't have two variables with the same identifier; however
		// here because n is being declared inside namespace B its full name is B::n 
		// which is not the same as the A::n defined above
}

#include <iostream>

//our main function
int main() {
	A::n = 10; //in order to refer to are first n (defined in namespace A)
		// we need to prefix the variable's name with the namespace's name
		// (i.e. used its full name)
	A::x = 3.14; //same here
	B::n = -1 //we are using a different variable here (the second n, the one from namespace B)

	//note that we have to use cout's full name because we omitted the line "using namespace std;" 
	std::cout << A::n << '\n';
	std::cout << A::x << '\n';
	std::cout << B::n << '\n';

	int n = 7; //here the full name of this variable is n (no prefix)
		// because it's declared in the global namespace

	std::cout << n << '\n'; //uses the n from the global namespace
	// std::cout << x << '\n'; //Error! there is no x in the global namespace
	// std::cout << B::x << 'n'; //Error! x is not defined in namespace B
}

Example's output:

10
3.14
-1
7

So by defining your function hello in your own namespace, you ensure that any other hello functions defined will not break your program.