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Join Date: Jan 2007

Posts: 200

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shouvik.d

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Private Access

Jan 5th, 2007

Say if we ve certain private methods along with private data members and public methods.
other than friend function is thr any other way we access these members(they being private only) directly. its one of the requirements in a project of mine.
The real prob comes when accessing function.
say we've classes ported to us in .obj format. then going for DMA using pointers is a risky n unreliable job.

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
class x
{
private:
void meth1()
{
cout<<"Meth1";
}
void meth2()
{
cout<<"meth 2";
}
};
class xduplicate
{
public:
void virtual meth1();
void virtual meth2();
};
main()
{
x obj;
xduplicate *obj1;
obj1=(xduplicate *)&obj;
obj1->meth1();
}
class x
{
private:
void meth1()
{
cout<<"Meth1";
}
void meth2()
{
cout<<"meth 2";
}
};
class xduplicate
{
public:
void virtual meth1();
void virtual meth2();
};
main()
{
x obj;
xduplicate *obj1;
obj1=(xduplicate *)&obj;
obj1->meth1();
}

we can access meth1 only if in class x it is virtual. i.e. the entry is in the virtual table.
But now i cant jst change the native code ported to us. i've to anyhow access the private methods without any change in native code.
wht we're plannin is x will be the producer class n xduplicate the consumer class.
x will be available as .obj along with .h file
so how can 1.

though one of the cheap n unprofesssional sol is

Help with Code Tags

c Syntax (Toggle Plain Text)

#define private public

but this unwantedly unveals many non required methods toopen arena

plz hlp

Last edited by shouvik.d; Jan 5th, 2007 at 3:58 am.

Regards
Shouvik

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Join Date: Dec 2006

Posts: 209

Reputation: Ravalon is on a distinguished road

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Ravalon

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Re: Private Access

Jan 5th, 2007

•

Originally Posted by shouvik.d

Say if we ve certain private methods along with private data members and public methods.
other than friend function is thr any other way we access these members(they being private only) directly. its one of the requirements in a project of mine.

The only other safe way is a member function of a friend class. I can think of three unsafe ways to do it, but they're all hit or miss and they all break something serious. I think you might be misunderstanding the requirement for your project.

•

Originally Posted by shouvik.d

though one of the cheap n unprofesssional sol is
Help with Code Tags

c Syntax (Toggle Plain Text)
#define private public
#define private public
but this unwantedly unveals many non required methods toopen arena

It's also not allowed. The language standard doesn't let you redefine keywords. It's also not sure to work if the private section isn't explicit. For example.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
class x
{
  void meth1()
  {
    cout<<"Meth1";
  }
  void meth2()
  {
    cout<<"meth 2";
  }
};
class x
{
  void meth1()
  {
    cout<<"Meth1";
  }
  void meth2()
  {
    cout<<"meth 2";
  }
};

The default access level of a class is private, but your trick won't work with the above class because it doesn't use the private keyword explicitly. It also won't work if you don't have access to the source code because by the time a class is compiled to object code, the keywords are long gone and the preprocessor from client code won't be able to touch it.

The simple answer is that you can't do what you're asking. The complicated answer is that you can do anything if you have sufficient knowledge of how the internals of the compiler work, but it's not portable and it's more likely to seriously screw something up than do any good.

It's hard to be humble when you're as gifted as I am at pretending to be an expert.

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Join Date: Feb 2006

Posts: 486

Reputation: Bench has a spectacular aura about

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Bench

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Re: Private Access

Jan 5th, 2007

•

Originally Posted by Ravalon

It's also not allowed. The language standard doesn't let you redefine keywords.

Actually, I don't think there's anything which stops it. Consider the following code

 Help with Code Tags 
 CPP Syntax (Toggle Plain Text) 
#undef private
#define private public
 
int main()
{
}
#undef private
#define private public

int main()
{
}

On at least 2 different compilers in strict mode, this compiles without error nor warnings.

Although i still think its a very bad idea. And, as you correctly mention, this doesn't change the fact that a class defaults all its members to private.

for the OP - Re-read the requirements of your problem. It sounds to me as if you've probably misinterpreted it.

Last edited by Bench; Jan 5th, 2007 at 12:00 pm.

¿umop apisdn upside down?

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Ravalon

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Re: Private Access

Jan 5th, 2007

•

Originally Posted by Bench

Actually, I don't think there's anything which stops it. Consider the following code
Help with Code Tags

CPP Syntax (Toggle Plain Text)
#undef private
#define private public
 
int main()
{
}
#undef private #define private public int main() { }
On at least 2 different compilers in strict mode, this compiles without error nor warnings.

The compilers might let it slide, but the language standard says it's undefined behaviour. That's legalese for 'not allowed'.

It's hard to be humble when you're as gifted as I am at pretending to be an expert.

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Join Date: Feb 2006

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Bench

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Re: Private Access

Jan 5th, 2007

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Originally Posted by Ravalon

The compilers might let it slide, but the language standard says it's undefined behaviour. That's legalese for 'not allowed'.

In which case I stand corrected

I haven't got access to a copy of the standard right now - although i'm somewhat surprised that Comeau allowed that through without even throwing a warning.

¿umop apisdn upside down?

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Join Date: Dec 2006

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Ravalon

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Re: Private Access

Jan 5th, 2007

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Originally Posted by Bench

I haven't got access to a copy of the standard right now

Me neither. I'm just going by memory, and I could very well be wrong.

•

Originally Posted by Bench

although i'm somewhat surprised that Comeau allowed that through without even throwing a warning.

If I remember correctly, redefining a keyword is undefined if a header is included but nothing is said about when a header isn't included. So your snippet might be well defined but pretty much any practical use is not. That might be hard to check for and the reason why Comeau was silent. It doesn't throw a warning if you include a header either.

It's hard to be humble when you're as gifted as I am at pretending to be an expert.

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Join Date: Jan 2007

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Reputation: shouvik.d is an unknown quantity at this point

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shouvik.d

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Re: Private Access

Jan 5th, 2007

I couldn't make private definition to public
as it threw the followind error in VC++ 6.0

LIBCD.lib(wincrt0.obj) : error LNK2001: unresolved external symbol _WinMain@16
Debug/pvt.exe : fatal error LNK1120: 1 unresolved externals

Regards
Shouvik

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Join Date: Dec 2006

Posts: 209

Reputation: Ravalon is on a distinguished road

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Ravalon

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Re: Private Access

Jan 5th, 2007

•

Originally Posted by shouvik.d

I couldn't make private definition to public
as it threw the followind error in VC++ 6.0

LIBCD.lib(wincrt0.obj) : error LNK2001: unresolved external symbol _WinMain@16
Debug/pvt.exe : fatal error LNK1120: 1 unresolved externals

That looks like a different problem, you're using console mode code in a Win32 mode project. It expects WinMain() as the entry point instead of main().

It's hard to be humble when you're as gifted as I am at pretending to be an expert.

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Join Date: Jan 2007

Posts: 200

Reputation: shouvik.d is an unknown quantity at this point

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shouvik.d

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Re: Private Access

Jan 5th, 2007

it isn't a console based application.

Simple win32 appl. and main() itself is working as an entry point if i remove the lines

Help with Code Tags

c Syntax (Toggle Plain Text)

#undef private
#define private public

Regards
Shouvik

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Join Date: Dec 2006

Posts: 209

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Ravalon

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Re: Private Access

#10

Jan 5th, 2007

•

Originally Posted by shouvik.d

it isn't a console based application.

Simple win32 appl. and main() itself is working as an entry point if i remove the lines
Help with Code Tags

c Syntax (Toggle Plain Text)
#undef private
#define private public
#undef private #define private public

Right. You're using main() as the entry point, like this.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
int main()
{
  return 0;
}
int main()
{
  return 0;
}

But because it's a Win32 application, the runtime code is looking for WinMain() and not main().

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <windows.h>
 
int WINAPI WinMain( HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow )
{
  return 0;
}
#include <windows.h>

int WINAPI WinMain( HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow )
{
  return 0;
}

The linker throws that error to tell you that it can't find WinMain.