[C++] static members in a class ?

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C++

#include "stdafx.h"

class Animal
{
public:
	static int ID;
};

int main()
{
	Animal::ID = 5;
	printf("%d \n", Animal :: ID);
	return 0;
}

Whats wrong with this ???

What I have tried:

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Posted 30-Jul-17 9:07am

The_Unknown_Member

Updated 30-Jul-17 20:00pm

v2

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Thomas Daniels 30-Jul-17 15:15pm

Could you please describe what you mean by "what's wrong"? Do you receive a compiler error? Runtime crash? And which compiler are you using?

The_Unknown_Member 30-Jul-17 16:33pm

Not compiling. Here is the error message (its a screenshot just open the link):
https://i.gyazo.com/bfd20571fb65d0ed231aa5c10720065d.png

Richard MacCutchan 31-Jul-17 3:24am

You never instantiate an Animal object, so ID does not exist in your program.

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Kornfeld Eliyahu Peter · Accepted Answer · 2017-07-30T20:00:00

Solution 1

The problem i that you missing the definition part (you only have the declaration part) and that leads to an incomplete type...
You can fix it like this...

C++

class Animal
{
public:
	static int ID;
};

int Animal:ID;
 
int main()
{
	Animal::ID = 5;
	printf("%d \n", Animal::ID);
	return 0;
}

A much better expatiation is here: static members - cppreference.com[^]

Posted 30-Jul-17 20:00pm

Kornfeld Eliyahu Peter

Comments

CPallini 31-Jul-17 3:52am

5.

Kornfeld Eliyahu Peter 31-Jul-17 3:53am

Thank you!