Class enumerator values cannot be passed as parameters to another class's function

Question

In a program I'm making, I'm trying to get a certain class to pass data to another class's function as a parameter. This data happens to be a variable from the first class's member enumerator. But I'm getting a lot of errors. The code below is an example of what I'm trying to do. I've added the errors in the comments above their lines:

main.cpp:

#include "A.h"

int main(int argc, char* args[]) {
    A a;

    a.callFunctionB();

    return 0;
}

A.h:

#pragma once
#include "B.h"

class B;

class A {
public:
    enum Enumerator {x, y, z};
    void callFunctionB();
private:
    //C2146: syntax error : missing ';' before identifier 'b'
    //C4430: missing type specifier - int assumed.
    B b;
    Enumerator e = x;
};

A.cpp:

#pragma once
#include "A.h"

void A::callFunctionB() {
    //C2660: 'B::functionB' : function does not take 1 arguments
    b.functionB(e);
}

B.h:

#pragma once
#include "A.h"

class A;

class B {
public:
    //C2653: 'A': is not a class or namespace name
    //C2061: syntax error : identifier 'Enumerator'
    //C2653: 'A' is not a class or namespace name
    void functionB(A::Enumerator e);
};

B.cpp:

#pragma once
#include "B.h"
#include <iostream>

void B::functionB(A::Enumerator e) {
    std::cout << "It worked! Enumerator variable 'x' was passed to function B." << std::endl;
}

Why can't I send the variable of one class's member enumerator as a parameter to another class's function?

I think you have an include problem here. `B.h` includes `A.h` but `A.h` also includes `B.h`. — Telokis, Jun 09 '15 at 11:07

score 3 · Accepted Answer · edited May 23 '17 at 11:58

3

You have a circular dependency problem. Your files can include each other all they want, but the

#pragma once

at the top means that only one sees the other one; not that each sees the other.

There are several ways to go here.

One way would be to remove the enumerator of A outside the class (possibly to some more private namespace). In general, you want your classes to "know as little as possible" about each other in any case.

edited May 23 '17 at 11:58

Community

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answered Jun 09 '15 at 11:09

Ami Tavory

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Thanks for your answer. That's a good link :) But I'm wondering if I should forget trying to use the enumerator for a parameter in my program. I'm curious about the use of namespaces though: In this example, if the enumerator is needed by both class A and class B functions, where would you put the namespace? The namespace can only be used in files that include the file where it was created, right? – Jun 10 '15 at 07:32
It really depends on the case, but perhaps you could try with some header file that both classes include. That would break the circular dependency. – Ami Tavory Jun 10 '15 at 07:33

Class enumerator values cannot be passed as parameters to another class's function

1 Answers1