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Hide implementation by using a pointer (Pimpl idiom)

Asked 2012-11-06T17:51:03.713
11

Is it somehow possible, to accomplish the following:

x.hpp - this file is included by many other classes

class x_impl; //forward declare
class x {
    public:
        //methods...
    private:
        x_impl* impl_;
};

x.cpp - the implementation

#include <conrete_x>
typedef concrete_x x_impl;    //obviously this doesn't work
//implementation of methods...

So basically, I want the users to include the file x.hpp, but be unaware of the conrete_x.hpp header.

Since I can use concrete_x only by a pointer and it appears only as a private data member, a forward declaration should be enough for the compiler to know how much space to prepare for it. It looks quite like the well-known "pimpl idiom".

Can you help me with this?

PS. I don't want to use a void* and cast it around..

c++ dependencies pimpl-idiom
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1 Answer

5

As an alternative to the answer from @Angew, if the name concrete_x should not be made known to users of class x, you could do this:

in x.hpp

class x_impl;
class x {
  public:
    x();
    ~x();
    //methods...
  private:
    x_impl* impl_;
};

in x.cpp

#include <concrete_x>
class x_impl : public concrete_x { };

x:x() : impl_(new x_impl) {}
x:~x() { delete impl_; }
answered 2012-11-06T18:20:12.350

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