Is it possible to access private members of a clas

问题:

Is it possible to access private members of a class in c++.

provided you don't have a friend function and You don't have access to the class definition

回答1:

You mean using some pointer arithmetic to gain the access ? It is possible but is definitely dangerous. Take a look at this question also: Accessing private members

回答2:

I think there was some old school trick like this:

#define private public
#include "header.h"
#define private private

But you are strongly discouraged to do this (I've read quickly that the said something about this in the C++ standard) - if you want to read more about this google for "#define private public"

回答3:

Well I might be talking rubish, but I think you could try to define a "twin" class with same members as the class you want to modify but different public/private modifiers and then use reintepret_cast to cast the original class to yours in which you can access the private members.

Its a bit hacky ;-)

A bit of code to explain the idea:

class ClassWithNoAccess 
{
public:
  someMethod();

private:
  int someVar;
};

class ClassTwin 
{
public:
  someMethod();

public:
  int someVar;
}

and somewhere in the code:

ClassWithNoAccess* noAccess = new ClassWithNoAccess();
ClassTwin* twin = reinterpret_cast<ClassTwin *>(noAccess);
twin->someVar = 1;

edit: so like someone already wrote before, this might work but the standard does not guarantee the order of the variables with public and private modifier will be the same

回答4:

Even if it were possible through some nasty hack - see earlier posts - you SHOULD not do it.

Encapsulation exists for a very good purpose, and setting class member as private means that the developer did not intend anyone to mess around with that member. That should mean

"You don't have to access this member in order to use the public interface to it's full intended extent"