Undefined Reference to Static Class Member

Undefined reference to static class member

You need to actually define the static member somewhere (after the class definition). Try this:

class Foo { /* ... */ };

const int Foo::MEMBER;

int main() { /* ... */ }

That should get rid of the undefined reference.

Undefined reference to declared C++ static member variable [duplicate]

In C++, static variables are essentially syntactic sugar around global variables. Just like global variables, they must be defined in exactly one source file, with:

int Test::nb;

and if you want to initialize it with a particular value,

int Test::nb = 5; // or some other expression

Undefined reference to static variable [duplicate]

You only declared A::i, need to define A::i before using it.

class A  
{ 
public:     
  static int i;
  static void init(){
     i = 1;  
  }
 };

int A::i = 0;

int WINAPI WinMain (HINSTANCE hThisInstance,
                HINSTANCE hPrevInstance,
                LPSTR lpszArgument,
                int nFunsterStil)
{
  A::i = 0;
  A::init();

  return 0;
}

Also your init() function should return a value or set to void.

Undefined reference to static member of class

In Rules.cpp, you don't define the static members Rules::suits and Rules::ranks, but rather introduce 2 new global variables.

In order for the static definition to work, you need to specify the fully qualified name, e.g. Rules::suits.

What does it mean to have an undefined reference to a static member?

To understand this, you should have a good understanding of compiling and linking, and the differences between declarations and definitions.

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Consider the following class:

//In header file
class Example {
    static bool exampleStaticMember;
};

Here, exampleStaticMember is declared but not defined. This means that if exampleStaticMember is used in a way that means that it must have an address then there must be a separate definition for it. In general, no declaration of a static data member in a class definition is a definition of that member.

The required declaration is usually put in the cpp file which contains the other definitions for the members of the class. It must be in the same namespace as the class definition. The definition typically looks like:

//In source file:
//This may optionally have an initialiser (eg "= true")
bool Example::exampleStaticMember; 

The definition can be put in any cpp file, but it should not be put in the header with the class, because that would be likely to break the One Definition Rule.

As a special case, if the static member variable is an const integral or enumeration type then it can have an initialiser in the class definition:

//In header file
class Example {
    static const int initialised = 15;
};

In this case, the definition in the cpp file is still required, but it is not allowed to have an initialiser:

//In source file
//Note: no initialiser!
const int Example::initialised;

Static members that have been initialised like this can be used in constant expressions.

Templates

For a static data member of a template, things are slightly different. The static member should be defined in the header along with the rest of the class:

//In header file
template<typename T>
class Example {
    static int exampleInt;
    static T exampleT;
}
template<typename T> int Example<T>::exampleInt;
template<typename T> T Example<T>::exampleT;

This works because there is a specific exception to the One Definition Rule for static data members of class templates.

Other uses of static

When the static keyword is applied to functions and objects that are not in a class scope it can take on a very different meaning.

When applied to objects in a function scope, it declares an object that is initialised in the first execution of the function and that subsequently keeps its value between function calls.

When applied to objects or functions at namespace scope (outside of any class or function definition), it declares objects or functions with internal linkage. This usage is deprecated for objects, as the unnamed-namespace provides a better alternative.

undefined reference to static member variable in a static member function [duplicate]

Put this in a source file (by the looks of it MapObject.cpp)

#include "MapObject.h"

float MapObject::xoffset = 0;
float MapObject::yoffset = 0;


//... the rest of your MapObject code here...

In C++ non-const static members must be both declared in the class definition and defined with global scope to properly give the linker something to reference.

linking static class member function throws undefined reference error c++

In the samp.cpp file you define test class again.

You need to include samp.h header and implement methods of test class:

#include "samp.h"

using namespace std;

test::test()
{
    cout << "priv cont called\n";
}

void test::const_caller()
{
    cout << "calling priv const\n";
}

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