Learning Classes C++ - Can't set values in an array of classes nested within another class.

Question

I am super-new to classes and still wrapping my brain around how they work. Any help/advice/pointers-> are appreciated!

I have two classes. Within the second class is an array of the first class. I am trying to assign values to the private member variables contained in the array of the first class.

I get this error message when compiling:

hw2Test.cpp: In member function 'void bar::set(int)':
hw2Test.cpp:11:7: error: 'int foo::x' is private
   int x;
       ^
hw2Test.cpp:34:12: error: within this context
  foodoo[0].x = x;
            ^

Here is the code:

#include <iostream>
using namespace std;


class foo
{
    public:


    private:
        int x;
};

class bar
{
    public:
        void set(int x);

    private:
        foo foodoo[1];
};

int main()
{
    bar tar;

    tar.set(1);

    return 0;
}

void bar::set(int x)
{
    foodoo[0].x = x;
}

Remy Lebeau · Accepted Answer · 2016-06-03 23:44:09Z

1

foo::x is declared as private, so only methods of foo can access it. But you are trying to access x inside of a method of bar instead, which does not have access to foo's private members.

To give bar access, you need to either:

declare foo::x as public:

class foo
{
    public:
        int x;
};

void bar::set(int x)
{
    foodoo[0].x = x;
}

declare a public setter:

class foo
{
    public:
        void set(int i);

    private:
        int x;
};

void foo::set(int i)
{
    foodoo[0].x = i;
}

void bar::set(int x)
{
    foodoo[0].set(x);
}

declare bar as a friend of foo:

class foo
{
    public:

    private:
        int x;

    friend class bar;
};

void bar::set(int x)
{
    foodoo[0].x = x;
}

edited Jun 3, 2016 at 23:44

answered Jun 3, 2016 at 23:35

Remy Lebeau

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3 Comments

bodangly Over a year ago

There is a third option, provide accessor methods.

Buck Wheat Over a year ago

By provide accessor methods, do you mean calling a fx inside of bar that calls a fx inside of foo so I can get to foo's naughty bits?

Remy Lebeau Over a year ago

@BuckWheat yes, exactly

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