Question

I think the mistake i’m doing it’s so stupid but i don’t know what i’m doing wrong.
I have a class with static and non-static vars and some methods, all public.
In my program i want to create an object and pass this object to a general method by reference.

The program doesn’t compile and the compiler throws really weird error messages.

Undefined symbols for architecture x86_64: “prueba::num”, referenced
from:
_main in ccbRZYqe.o
metodoC(prueba*) in ccbRZYqe.o
prueba::prueba()in ccbRZYqe.o
prueba::inicio() in ccbRZYqe.o “prueba::flag”, referenced from:
metodoC(prueba*) in ccbRZYqe.o
prueba::prueba()in ccbRZYqe.o
prueba::inicio() in ccbRZYqe.o ld: symbol(s) not found for architecture x86_64 collect2: ld returned 1 exit status

Code

#include <iostream>

using namespace std;

class prueba
{
    private:
    public:
        static bool flag;
        static int num;
        float complejo;

        // Metodos
        //--------------
        prueba()
        {
            flag = false;
            num = 0;
            complejo = 0.0; 
        }

        void inicio()
        {
            flag = true;
            num = 5;
            complejo = 3.2;
        }

        bool cambio()
        {
            flag++;
            num++;
            complejo++;
        }
};

bool metodoC(prueba* ensayo)
{
    cout << "-----------------------------------------" << endl;
    cout << "- flag: " << ensayo->flag << endl;
    cout << "- num: " << ensayo->num << endl;
    cout << "- Complejo: " << ensayo->complejo << endl;
    cout << "-----------------------------------------" << endl;

    return true;
}

//-----------------------------------
//      M   A   I   N
//-----------------------------------
int main(int argc, char *argv[]) 
{
    prueba test;

    test.inicio();

    test.num += 2;
    test.complejo += 5.2;

    metodoC( &test );

    return 0;
}

Answer 1

You need to define your static members. They are only declared.

class prueba {
  // as before
};

and in the implementation file:

bool prueba::flag=false;
int prueba::num=0;

Note that you shouldn’t put the definitions in a header because you will get a definition of the statics for each translation unit. You need to put them in an implementation file that is then used to make a single object file that clients can build against.

Be careful though, each time you instantiate a new prueba object, you reset the static members in the constructor.