C++ : Undefined reference in Map::insert

Question

Somewhere in a .h file:

namespace gpBenchAPI {
 struct AbstractConsts {
  public:
    static const uint8_t STATUS_TAG_NOT_FOUND = 2;
 }; //AbstractConsts
}

Somewhere in another .h file:

class MyClass{
private:
     void method();
     QMap<uint8_t, QString> errorCodes;
};

Somewhere in a .cpp file:

   void MyClass::method(){
       using namespace gpBenchAPI;
       errorCodes.insert(AbstractConsts::STATUS_TAG_NOT_FOUND, "A-1");
   }

This code is rising a linking error:

  undefined reference to `gpBenchAPI::AbstractConsts::STATUS_TAG_NOT_FOUND'

but this code compiles and links:

 switch (status) {
    case AbstractConsts::STATUS_TAG_HUNTING:
        return 0;
  }

If I do :

 errorCodes.insert(2, "A-1");

no problem. Why?

Added: If, like in the suggested dupplicated question's answer, I initialize the const in a cpp file like this:

const uint8_t AbstractConsts::STATUS_TAG_NOT_FOUND = 2;

and remove the initialization from the .h file, the "switch" does not compile anymore:

The value of 'gpBenchAPI::AbstractConsts::STATUS_TAG_NOT_FOUND' is not usable in a constant expression
     case AbstractConsts::STATUS_TAG_NOT_FOUND:
                          ^

https://stackoverflow.com/questions/2605520/c-where-to-initialize-static-const read the small print in the most voted answer — Alessandro Teruzzi, Apr 10 '18 at 16:05
@AlessandroTeruzzi, added some info, taking into account the most voted answer. — Julien, Apr 10 '18 at 17:31
As Allessandro implies, if you read the comment to the top answer, you need to *define* the variable in the .cpp **but not initialize it there** (leave the initialization in the header). — Martin Bonner supports Monica, Apr 11 '18 at 07:13
@eyllanesc: In this case, I will because it makes sense but sometimes not and I wanted to know why. — Julien, Apr 13 '18 at 15:57

C++ : Undefined reference in Map::insert

0 Answers0