How to implement the Delphi protected member access trick in C++ builder? - delphi

Question

I need access to TControlItem.InternalSetLocation which is protected. I Delphi you would do
type
THackControlItem = class(TControlItem);
How do you do this in C++ Builder?

Answer 1

As in Delphi, you need to inherit the class but also override and make public the protected function. However, I wouldn't recommend to use it in production code.
class THackControlItem : public TControlItem
{
public:
void __fastcall InternalSetLocation(int AColumn, int ARow, bool APushed, bool MoveExisting)
{
TControlItem::InternalSetLocation(AColumn, ARow, APushed, MoveExisting);
}
};
In the program
TControlItem* ci = ...;
static_cast<THackControlItem*>(ci)->InternalSetLocation(...);

Answer 2

This is a nice trick I think Remy Lebeau showed me but can not find the QA anymore...
//---------------------------------------------------------------------------
#ifndef _TDirectMemoryStream
#define _TDirectMemoryStream
class TDirectMemoryStream:TMemoryStream // just for accessing protected SetPointer
{
public:
void SetMemory(BYTE *ptr,DWORD siz) { SetPointer(ptr,siz); Position=0; };
};
#endif
//---------------------------------------------------------------------------
You simply create new class that is descendant of the class you want to access. Now just add get/set functions for the protected members ...
Now usage:
TMemoryStream *mem=new TMemoryStream(); // original class instance you want to access
// overtype to our new class and access/use you get/set ...
((TDirectMemoryStream*)(mem))->SetMemory(hdr->lpData,hdr->dwBytesUsed);
delete mem; // release if not needed anymore
I am using it btw to feed a memory stream with custom memory data hdr coming from vfw camera so I can properly decode it using TJPEGImage class instead of writing the data into file and loading it back each frame ...
Here another example:
class A
{
protected:
int x;
public:
int getx(){ return x; }
};
class hack_A:A
{
public:
void setx(int _x){ x=_x; }
};
void test()
{
A a;
hack_A *ha=(hack_A*)&a;
ha->setx(10);
a.getx(); // print the x somwhere
}
However this will not work for private members ... In such case its doable too but requires access to A source code:
class A
{
protected:
int x;
private:
int y;
public:
int getx(){ return x; }
int gety(){ return y; }
friend class hack_A; // but this one requires access to A soourcecode
};
class hack_A:A
{
public:
void setx(int _x){ x=_x; }
void sety(int _y){ y=_y; }
};
void test()
{
A a;
hack_A *ha=(hack_A*)&a;
ha->setx(10);
ha->sety(20);
a.getx(); // print the x somwhere
a.gety(); // print the x somwhere
}