c++ static member

[pdk123]

I have a approximate following class

class ClassA : public ClassB
{
    void                        HandleMessages(const u8 *pP, const u16 nMsgBodyLen);

    static std::map<std::pair<u32, u32>, CreateSessInfo> m_mSessionId2CCRNum2DefaultBearerId;

};

When trying to access the map from the HandleMessage, I am getting the linker error, saying the
undefined reference to m_mSessionId2CCRNum2DefaultBearerId;

Could some c++ experts help me

[NathanOliver]

You have to initialize the static member outside of the class.

/Foo.h
class Foo
{
    static int bar;
    //...
};


// Foo.cpp
int Foo::bar = 1;

If the initialization is in the header file then each file that includes the header file will have a definition of the static member. Thus during the link phase you will get linker errors as the code to initialize the variable will be defined in multiple source files.

[phorce]

You have not declared the method prototype correctly in your class.

static std::map<std::pair<u32, u32>, CreateSessInfo> m_mSessionId2CCRNum2DefaultBearerId;

Shoudl be:

static std::map<std::pair<u32, u32>, CreateSessInfo> m_mSessionId2CCRNum2DefaultBearerId()
{
    // Logic here

    return map; 

}

Then you can access it as:

Foo::m_mSessionId2CCRNum2DefaultBearerId();

Here, I did a similar example: http://ideone.com/NelSt9 no logic is there, but, I hope it gives you an understanding of where you went wrong.

EDIT:

Just realised what you were attempting, so, @NathanOliver answer is more accurate.

[pdk123]

Thanks a lot Nathan and Phorce. This issue is solved now

[pdk123]

It was my mistake, just to reconfirm that now issue is solved, after defining the map in the .cpp file.

[NathanOliver]

You have to initialize the map. Take a look at this post As how you can do that with or without C++11 support.