I have some understanding problems in C++ with parameterised constructors. If I have a class with one constructor which have two function parameters, how can i instantiate it in an other class header file?
For example:
public:
MyFunction myfunction(param1, param2); //makes an error
How can i declare an object like this?
You need to write MyFunction myfunction; in the class declaration.
Then in the member initialiser list of the constructor to the class of which myfunction is a member, write
/*Your constructor here*/ : myfunction(param1, param2)
{
/*the constructor body*/
}
The bit after the colon is the member initialiser list. param1 and param2 are obviously arguments to that constructor.
You have several ways:
struct P
{
P(int a, int b) :a(a), b(b){}
int a;
int b;
};
struct S
{
S() : p1(4, 2) {} // initializer list
P p1;
P p2{4, 2}; // since c++11
P p3 = P(4, 2); // since c++11
};
P p2{4, 2} actually calls the constructor, unlike C?
An option is having a predeclaration and a pointer to the class.
classA.h
class A
{
public:
A(a,b);
};
classB.h
class A;
class B{
public:
A* foo;
B();
~B();
}
classB.cpp
#include classA.h
#include classB.h
B()
{
foo=new A(a,b);
}
~B()
{
delete(foo);
}
As far as I understand, the problem is that MyFunction has only one constructor that only accepts two arguments.
You can use a pointer to that object and then initialize it in the constructor:
#include <memory>
class Something {
public:
std::shared_ptr<MyFunction> data;
Something(int par1, int par2) {
data = std::shared_ptr<MyFunction>(new MyFunction(par1, par2)); // here you go!
}
~Something() {
//delete data; no need to do this now
}
};
Edit: added a smart pointer to follow rule of three.
param1andparam2types?