CODEWITHSUNDEEP
c++structconstructor
Perotto
Perotto

Reputation: 336

Struct inside struct: 'Illegal reference to non-static member' error

I need to create a struct inside struct. How to code the constructor correctly? Do I need to create two constructors separately for A and B or can I use only one 'outside' constructor for A like in example below? My attempts resulted in C2597 error.

struct A
{
    struct B
    {
        unsigned n;
        int* d;
    };

    A(unsigned c)
    {
        B::n = c; // C2597
        B::d = new int[c]; // C2597
    }
};

Upvotes: 1

Views: 242

Answers (3)

Swift - Friday Pie
Swift - Friday Pie

Reputation: 14589

You didn't declare a member, in your code B is a nested class of class A.

You have to declare a member of that class.

struct A
{
    struct B
    {
        unsigned n;
        int* d;
    }; // this is a class-type declaration

    B data; // this is member of class A having type of class B

    A(unsigned c) 
    {
        data.n = c; 
        data.d = new int[c]; 
    }
};

Upvotes: 2

Dmitry Gordon
Dmitry Gordon

Reputation: 2324

You need either to make members of B static (but in this case you will have one value for whole program or dll in case of Windows):

struct A
{
    struct B
    {
        static unsigned n;
        static int* d;
    };

    A(unsigned c)
    {
        B::n = c;
        B::d = new int[c];
    }
};

or create an instance of the B:

struct A
{
    struct B
    {
        unsigned n;
        int* d;
    };

    A(unsigned c)
    {
        B b;
        b.n = c;
        b.d = new int[c];
    }
};

If you meant A to contain B - that is what you need to do:

struct A
{
    struct B
    {
        unsigned n;
        int* d;
    } b;

    A(unsigned c)
    {
        b.n = c;
        b.d = new int[c];
    }
};

Upvotes: 5

Bathsheba
Bathsheba

Reputation: 234715

You need an instance of B in order to access the members n and d.

struct B
{
    unsigned n;
    int* d;
} b; // Create an instance of `B`

A(unsigned c)
{
    b.n = c;
    b.d = new int[c]; // ToDo - you need to release this memory, perhaps in ~B()
}

Either that or make them static.

Upvotes: 3

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