CODEWITHSUNDEEP
c++templatesnamespacesprivate
kbirk
kbirk

Reputation: 4022

Namespace template functions and hidden namespace variables

I am writing a namespace that requires certain functions inside to have access to a particular variable (also declared within the namespace). Normally when I do this, I have the variable declared in the .cpp file to prevent outside access to it.

.h

namespace Example
{
    int myFunc();
}

.cpp

namespace Example
{
    int hiddenVar;

    int myFunc()
    {
        .. do something with hiddenVar
        return someValue;
    }
}

My problem is that I need to define a template function that requires access to this hidden variable. Unfortunately since the body of the template function must be defined in the header file it wont have access to the variable hidden in the .cpp.

.h

namespace Example
{
    template< typename T >
    void myFunc( const T& myT )
    {
         .. do something with hiddenVar  // doesnt know what hiddenVar is
    }
}

.cpp

namespace Example
{
    int hiddenVar;
}

Is there anyway to have a variable hidden within a namespace while giving a template function in the header access to it?

Upvotes: 2

Views: 871

Answers (3)

Wilbert
Wilbert

Reputation: 7399

Put it in a nested namespace called 'Details' and stop worrying.

'Hiding' a variable using namespaces and private etc are not security-constructs, but there to facilitate better code.

Upvotes: 0

Gorpik
Gorpik

Reputation: 11028

You cannot do this directly, but you can use a function. Since hiddenVar does not depend on the template parameters, you can do this:

.h

namespace Example
{
  void Function(); // Use the right function prototype here, of course,
                   // as long as it does not depend on T

  template<typename T>
  void myFunc(const T& myT)
  {
    //...
    Function();
    //...
  }
}

.cpp

namespace Example
{
  int hiddenVar;
  void Function()
  {
    // Do something with hiddenVar
  }
}

If your use of hiddenVar depends on T, of course, you are out of luck.

Upvotes: 0

SergV
SergV

Reputation: 1277

.h:

namespace Example
{
  int * get_hiddenVar();  
  template< typename T >
  void myFunc( const T& myT )
  {
     int *  hiddenVarPtr = get_hiddenVar();
     .. do something with *hiddenVarPtr  
  }
}

.cpp

namespace Example
{
   int hiddenVar=0;
   int * get_hiddenVar()
   {
      return &hiddenVar;
   }
}

Upvotes: 1

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