Call constructor of a member variable without 'new'

Question

I want to call the constructor of a member m_foo of Class A in the constructor of Class A . Is it nessecary to call it with m_foo = new Foo() ? Or can I call it without putting it on the Heap? I want to pass a pointer to an array of 256 Byte, so that the Foo object fills its member array with the data the pointer points to. But how would I call a contructor of a member variable that I declare in the headerfile?

A.hpp

class A{ 

 public
 A();

 private:
 Foo m_foo;

};

A.cpp

 A::A()
{
 //How to call constructor of class Foo here?


}

Foo.hpp

class Foo()
{
 Foo(char* p)
 {
  memcpy(m_Array, p, sizeof(m_Array)/sizeof(m_Array[0]));
 }
  private:
 char m_Array[256];
};

Answer 1

Use the member initialization list for the A constructor :

 A::A() : m_foo(...)
 {


 }

---

You can get the char* required to build m_foo from :

A constructor :

A::A(char* p) : m_foo(p) {}

Or another function :

A::A() : m_foo(GetBuffer()) {}

Answer 2

If you don't mind passing the pointer to A's constructor, this may be what you want:

class A
{ 
    public:
    A(const char* p);

    private:
    Foo m_foo;
};

A::A(const char* p) : m_foo(p) // <- calls Foo's ctor here
{
}