How can i initialize superclass params from within the child c-tor in C++?
Watch the following example:
开发者_开发百科class A {
public:
A(int param1, int param2, int param3) {
// ...
}
};
class B : public A {
public:
B() : m_param1(1), m_param(2), m_param(3), A(m_param1, m_param2, m_param3) {
// ...
}
};
B b;
Obviously, when "b" will be created, A's ctor will be called before the parameters of B will be initialized.
This rule prevents me from creating "wrapper" classes which simplify the class's initialization.
What is the "right way" for doing it?
Thanks, Amir
PS: In my particular case, the parameters are not primitives, this example just helped me to explain myself.
Just call A's constructor:
class B : public A
{
public:
B() : A(1 ,2, 3)
{
}; // eo ctor
}; // eo class B
EDIT:
Just read your comment to your original post. It's important to be clear about these things :) Anyway, this answer still holds true if you want to create new data in B, track it in B, and pass it to A:
class Object
{
private:
int i;
public:
Object(int _i) : i(_i){};
};
class A
{
public:
A(Object* _1, Object* _2, Object* _3)
{
};
};
class B : public A
{
private:
Object* _1;
Object* _2;
Object* _3;
public:
B() : A(_1 = new Object(1), _2 = new Object(2), _3 = new Object(3))
{
};
};
"The parameters are not primitives". So you have something like this?
class Param { /*...*/ };
class A {
public:
A(const Param& param1, const Param& param2, const Param& param3);
};
class B : public A {
public:
B();
private:
Param m_param1;
Param m_param2;
Param m_param3;
};
And you want to pass the members of B
to the constructor of A
. How about this?
class B_params {
protected:
B_params(int v1, int v2, int v3);
Param m_param1;
Param m_param2;
Param m_param3;
};
class B : private B_params, public A {
public:
B();
};
B_params::B_params(int v1, int v2, int v3)
: m_param1(v1), m_param2(v2), m_param3(v3) {}
B::B() : B_params(1,2,3), A(m_param1, m_param2, m_param3) {}
Just make sure B_params
comes before A
in the list of B
's inherited classes.
Not sure I'm getting your question.
If you just want something that helps you to initialize A with some given parameters, you should use an A constructor with default values:
class A {
public:
A(int param1 = 1, int param2 = 2, int param3 =3) {
// ...
}
};
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