Unable to initialize static map in class [duplicate]

Question

I am trying to initialise a static map of
map<string, int>
in my program as follows:

testApp.h

class testApp(){
public:
void setup();
void update();
void renew();
static map<string, int> _someMap;
};

testApp.cpp

testApp::setup(){
   _someMap["something"] = 1;
   _someMap["something2"] = 2;
cout<<_someMap["something"]<<"\n";
}

I don't want to use boost for this short use of map and add source dependency for my code. I am not on C++11 and I don't have the constructor here in the program since the class is some framework's class. I am on Xcode and on doing the above in .cpp, I get the following error:

Undefined symbols for architecture i386:
  "testApp::mapppp", referenced from:
      testApp::setup() in testApp.o
ld: symbol(s) not found for architecture i386
clang: error: linker command failed with exit code 1 (use -v to see invocation)

-- >Additionally, let's say my map is private, for which I tried doing this in my class:

...
private:
static someVariable;
static void someFunction();

.cpp

testApp::setup(){
someFunction();
}

Error:

Undefined symbols for architecture i386:
  "testApp::_someMap", referenced from:
      testApp::someFunction() in testApp.o
ld: symbol(s) not found for architecture i386
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Answer 1

You've declared the variable in the class definition, but it looks like you haven't defined it. Every static variable needs to be defined in exactly one translation unit. So add a definition to your source file:

map<string, int> testMap::_someMap;

If you like (and if you can't use a C++11 initialiser), you could avoid having to call the setup function by initialising the map from the result of a function instead:

map<string, int> make_map() {
    map<string, int> map;
    map["something"] = 1;
    map["something2"] = 2;
    return map;
}

map<string, int> testMap::_someMap = make_map();