CODEWITHSUNDEEP
c++staticprivatemember
Qaz
Qaz

Reputation: 1576

Can't set private static member variables with accessor

Zombie.h has some static member variables. Read.cpp, which includes Zombie.h, knows the values that need to go in those variables. I want read.cpp to set those variables with something along the lines of

int Zombie::myStaticInt = 4;

or

Zombie::setStaticVar(4);

I've tried everything I can think of, including using a public static accessor function and even making the static variables themselves public, but I've been getting a lot of "undefined reference" or "invalid use of qualified-name" errors. By looking into those I found out how to set Zombie.h's private static member variables from Zombie.cpp, but I don't have a Zombie.cpp file, just read.cpp. Can I set them from Read.cpp instead, and if so, how?

// In Zombie.h
class Zombie {
public:
    static void setMax(int a_in, int b_in, int c_in) {
        a = a_in;
        b = b_in;
        c = c_in;
    }
private:
    static int a, b, c;
}

// In read.cpp
#include "Zombie.h"
...
main() {
    int Zombie::a; // SOLUTION: Put this outside the scope of main and other functions
    int Zombie::b; // SOLUTION: Put this outside the scope of main and other functions
    int Zombie::c; // SOLUTION: Put this outside the scope of main and other functions
    int first = rand() * 10 // Just an example
    int second = rand() * 10 // Just an example
    int third = rand() * 10 // Just an example
    Zombie::setMax(first, second, third);
    return 0;
}

This yields (Updated) (Move first three lines of main outside of main() to solve this)

invalid use of qualified-name 'Zombie::a'
invalid use of qualified-name 'Zombie::b'
invalid use of qualified-name 'Zombie::c'

Upvotes: 0

Views: 1130

Answers (3)

Ronaldinho
Ronaldinho

Reputation: 135

Your problem is you haven't implemented Zombie class yet. Your code here:

zombie.h

#ifndef ZBE_H
#define ZBE_H

class Zombie
{
public:
    static int myStaticInt;

    Zombie();
};
#endif

read.cpp

#include <stdio.h>
#include <iostream>
#include "zombie.h"

int Zombie::myStaticInt = 1;

Zombie::Zombie()
{
}

int main()
{ 
    cout << "OOOK: " << Zombie::myStaticInt << endl;

    Zombie::myStaticInt = 100;

    cout << "OOOK: " << Zombie::myStaticInt << endl;

    return 0;
}

Upvotes: 0

user207421
user207421

Reputation: 310883

You have to define a,b,c somewhere. So far you've only declared them to exist. In some .cpp file, at the outer scope, you need to add:

int Zombie::a;
int Zombie::b;
int Zombie::c;

EDIT Re your edit, you can't put them inside a method. You have to put this at the outermost scope of the .cpp file.

Upvotes: 2

Mark Ransom
Mark Ransom

Reputation: 308138

Unlike non-static variables that get storage allocated in every object, static variables must have their storage outside of the class. You do this by creating definitions for the variables in a .cpp file. It doesn't matter which file they go in, although for convenience they should go with the code for the class.

int Zombie::a;
int Zombie::b;
int Zombie::c;

The linker error you're getting is telling you that these lines are missing.

Upvotes: 1

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