CODEWITHSUNDEEP
c++
dexterous
dexterous

Reputation: 6526

Is forward declaration is the only option in the C++ program?

Does C++ has any other alternative to forward declaration? For example, I have a class B that uses class A.

class B
{
    public:
    void set_classA_val( A &b);
};

class A
{
    private:
    int example;

};

Is there any alternative to resolve this compilation issue rather than placing the class A above class B? Do we have any other alternative? Is forward declaration is the only solution?

Upvotes: 3

Views: 133

Answers (3)

Vlad from Moscow
Vlad from Moscow

Reputation: 311048

Any name shall be declared before its using. If you do not like the following code

class A;

class B
{
    public:
    void set_classA_val( A &b);
};

then you can use elaborated type name in the parameter declaration of member function set_classA_val

class B
{
    public:
    void set_classA_val( class A &b);
};

Upvotes: 2

Zac Howland
Zac Howland

Reputation: 15870

There are a few options, but without more information about your goals, it is hard to tell you which is the best. Forward declaration, move the definition of A, and making B a template class are some of the options. Presuming you are familiar with the 2 former, the latter would look something like:

template<typename T>
class B
{
public:
    set_value(T& t);
};

And you would declare it for use using:

B<A> ba;

As jrok mentioned, you can also make the function itself a template - but the use would depend on how B is using the parameter (e.g. if the type is needed for other functions as well, it would probably be better to make the whole class utilize it).

Upvotes: 1

matekm
matekm

Reputation: 6030

Yes,

if You don't want to place A before B, then forward declaration is the only solution in that case (if You don't want to change definition of B - see Zac Howland answer for other ideas that change B). There is nothing wrong with that. Somehow, methods from B needs to know what A is (in that case it is a class). Either, compiler will figure it out by finding A definition or You will help the compiler with forward declaration.

Upvotes: 4

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