In a class with no virtual methods or superclass, is it safe to assume (address of first member vari
- by Jeremy Friesner
Hi all,
I made a private API that assumes that the address of the first member-object in the class will be the same as the class's this-pointer... that way the member-object can trivially derive a pointer to the object that it is a member of, without having to store a pointer explicitly.
Given that I am willing to make sure that the container class won't inherit from any superclass, won't have any virtual methods, and that the member-object that does this trick will be the first member object declared, will that assumption hold valid for any C++ compiler, or do I need to use the offsetof() operator (or similar) to guarantee correctness?
To put it another way, the code below does what I expect under g++, but will it work everywhere?
class MyContainer
{
public:
MyContainer() {}
~MyContainer() {} // non-virtual dtor
private:
class MyContained
{
public:
MyContained() {}
~MyContained() {}
// Given that the only place Contained objects are declared is m_contained
// (below), will this work as expected on any C++ compiler?
MyContainer * GetPointerToMyContainer()
{
return reinterpret_cast<MyContainer *>(this);
}
};
MyContained m_contained; // MUST BE FIRST MEMBER ITEM DECLARED IN MyContainer
int m_foo; // other member items may be declared after m_contained
float m_bar;
};
