pin_ptr on value struct is needed?

[Dusan Paulovic]

Hi all, I am working on class to wrapp unmanaged pointer. I am just confused, whether pinning of value struct is needed in C++/CLI, i.e. whether if I will not do it, it can cause some problems. In C#, I am not able to fix structs:

Point pntA = new Point(10, 25);
Point pntB = new Point();

unsafe
{
// Error 4
// You cannot use the fixed statement to take
// the address of an already fixed expression
fixed (Point* ptrA = &pntA, ptrB = &pntB)
{
ptrB->X = ptrA->X;
ptrB->Y = ptrA->Y;
}
}

but, I can simply use address-of operator:

Point pntA = new Point(10, 25);
Point pntB = new Point();

unsafe
{
// Correct
Point* ptrA = &pntA, ptrB = &pntB;
ptrB->X = ptrA->X;
ptrB->Y = ptrA->Y;
}

What is confusing me is that pin_ptr lets me pin structures as well as use address-of operator:

// /clr
generic where T : value struct
T GetValueA(void* ptr)
{
T val = Activator::CreateInstance();

pin_ptr valPtr = &val;
memcpy(valPtr, ptr, sizeof(T));
return val;
}

generic where T : value struct
T GetValueB(void* ptr)
{
T val = Activator::CreateInstance();

memcpy(&val, ptr, sizeof(T));
return val;
}

My questions are: Is pinning needed in C++/CLI functions to fix value struct before using its pointer in unmanaged function? Are value structs allocated in the unmanaged heap? Thanks all, Dusan