I have a class called A.
It has an instance or B:
public:
B inst;
B's constructor is like B::B(int, int).
When creating the A class's constructor A::A() { }, it gives me the following error:
No matching function for call to B::B()
when I haven't created or mentioned any B in A's constructor. Any idea?
Constructing A requires all of A's data members to be constructed. In this case, B must be default-constructed as you did not provide a member initialization list. As B defines a non-default constructor, generation of its implicit default constructor is suppressed - that's why you're getting the error.
When class A contains an instance of class B, constructing an instance of A also requires construction of the contained instance of B.
If no constructor of B is listed in the initialiser of class A, the default is to invoke a constructor of B that accepts no arguments. For example
class A
{
public:
A::A() {};
private:
B b;
};
is functionally equivalent to
class A
{
public:
A::A() : b() {};
private:
B b;
};
This involves a constructor of B with no arguments. If no such constructor exists, the result is a diagnostic (error message). Since you have declared/defined a constructor with arguments, a constructor for B with no arguments is not implicitly generated.
