CODEWITHSUNDEEP
c++pointers
skmic
skmic

Reputation: 79

Calling private function of a class outside using function pointer?

I solved a problem using function pointers and I am a little concerned with the solution and need advice.

I am having several classes in my project which implements a memory table, a local data structure which keeps some data in the memory.

All the functions are private so that no body other than the class itself can use/modify the data using it's own functions.

Recently I had a requirement where I had to use this data in a different module. As I did not want to make private functions as public so I stored the function pointer (of the required functions) of all the classes in a std:map at the app start. Later I simply called the function by these pointers wherever I needed to modify the data of that specific class.

I want to know if this correct? Calling a private function of a class inside a different class using the function pointer?

Below is the code which somewhat simulates what I tried to implement:

typedef struct
{
  void (*pfnDisplay)(void);
}FuncInfo;

std::map<int,FuncInfo> sFuncInfoMap;

//Stores the function pointer in a map
void RegisterFunction(void (*pfnDisplay)(void))
{
  FuncInfo sFuncInfo;
  sFuncInfo.pfnDisplay = pfnDisplay;
  sFuncInfoMap.insert ( std::pair<int, FuncInfo>(1, sFuncInfo) );
}

class A
{
private:
  static void Display(void)
  {
    printf("No one can access me");
  }
public:
  A()
  {
    RegisterFunction(Display);
  }
};

class B
{
  public:
  void CallADisplay()
  {
    sStFuncInfoMap[1].pfnDisplay();
  }
};


#pragma argsused
int _tmain(int argc, _TCHAR* argv[])
{
  A a;  //calls the constructor
  B b;
  b.CallADisplay();
  return 0;
}

**Output:**
No one can access me

Thank you.

Upvotes: 0

Views: 487

Answers (1)

Mike Seymour
Mike Seymour

Reputation: 254431

Yes, you can call a private function via a function pointer and, more generally, access any member indirectly via a pointer; although you can only create that pointer in a context where access is allowed.

Access control only prevents use of a member's name, not (indirect) access to the member itself.

Upvotes: 5

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