2 quick questions about passing by const pointer/const reference

1) Can someone explain the following?

void OnCreate(HWND hWnd, con开发者_如何转开发st LPCREATESTRUCT lpCreateStruct)
{
   lpCreateStruct->x = 2; // this compiles
}

void OnCreate(HWND hWnd, const CREATESTRUCT * lpCreateStruct)
{
   lpCreateStruct->x = 2; // this does not compile
}

2) Is it faster to pass by pointer or by reference? Or the same?

const LPCREATESTRUCT expands to CREATESTRUCT* const, i.e. a constant pointer to non-const structure, while const CREATESTRUCT* is a non-constant pointer to constant structure, so the compiler is right.

Why does the following assign 2 to x when it is const?

It shouldn't, any standard-compliant compiler makes that an error because ms points to a const my_structure.

edit:

With your updated case, its a problem of how typedefs work:

typedef T* TPtr;

void f(const TPtr);
void g(T* const);
void h(const T*);

Both f() and g() are equivalent and take a const pointer to a T, while h() a pointer to a const T.