Problems with temporaries and C++ spec

Problems with temporaries and C++ spec

[Garrett Kajmowicz]

I'm working on my own C++ library for embedded applications (cxx.uclibc.org) 
and while implementing valarray I came across a problem with private copy 
contructors.  The following code works in GCC 3.3.5, but not in GCC 3.4.2

#include <iostream>

class copy_to;

class hidden_copying{
public:
        friend class copy_to;
        friend class copy_from;

private:
        hidden_copying() : q(0) {  }
        hidden_copying(const hidden_copying &);
        hidden_copying & operator=(const hidden_copying &);
        int q;
};

class copy_to{
public:
        friend class copy_from;
        copy_to() : p (0) { }
        copy_to(const hidden_copying & h) : p(h.q) {  }
        int getval() const{
                return p;
        }
private:
        int p;
};

class copy_from{
public:
        friend class hidden_copying;
        copy_from() : r(0) {  }
        copy_from(const int i) : r(i) {  }
        copy_from(const copy_from & f) : r(f.r) {  }
        hidden_copying data() const{
                hidden_copying retval;
                retval.q = r;
                return retval;
        }

private:
        int r;
};


int main(){
        copy_from a(5);
        copy_to b(a.data());
        std::cout << "Value of copy_to: " << b.getval() << std::endl;
        return 0;
}

With gcc 3.4.2 I receive the following error message:
../temporarytest.cpp: In function `int main()':
../temporarytest.cpp:12: error: `hidden_copying::hidden_copying(const 
hidden_copying&)' is private
../temporarytest.cpp:48: error: within this context

Without breaking valarray spec (in the above case, amounting to making any of 
the copy constructors of hidden_copying public), how can I get the above code 
work work properly.   If There is no way, than please explain how to 
reconsile behaviors with spec definition of std::slice_array.

Thank you for your help.

-     Garrett

Re: Problems with temporaries and C++ spec

[corey taylor]

Why are you using a private copy constructor there in the first place?

corey

On 8/27/05, Garrett Kajmowicz <gkajmowi@tbaytel.net> wrote:
> I'm working on my own C++ library for embedded applications (cxx.uclibc.org)
> and while implementing valarray I came across a problem with private copy
> contructors.  The following code works in GCC 3.3.5, but not in GCC 3.4.2
> 
> #include <iostream>
> 
> class copy_to;
> 
> class hidden_copying{
> public:
>         friend class copy_to;
>         friend class copy_from;
> 
> private:
>         hidden_copying() : q(0) {  }
>         hidden_copying(const hidden_copying &);
>         hidden_copying & operator=(const hidden_copying &);
>         int q;
> };
> 
> class copy_to{
> public:
>         friend class copy_from;
>         copy_to() : p (0) { }
>         copy_to(const hidden_copying & h) : p(h.q) {  }
>         int getval() const{
>                 return p;
>         }
> private:
>         int p;
> };
> 
> class copy_from{
> public:
>         friend class hidden_copying;
>         copy_from() : r(0) {  }
>         copy_from(const int i) : r(i) {  }
>         copy_from(const copy_from & f) : r(f.r) {  }
>         hidden_copying data() const{
>                 hidden_copying retval;
>                 retval.q = r;
>                 return retval;
>         }
> 
> private:
>         int r;
> };
> 
> 
> int main(){
>         copy_from a(5);
>         copy_to b(a.data());
>         std::cout << "Value of copy_to: " << b.getval() << std::endl;
>         return 0;
> }
> 
> With gcc 3.4.2 I receive the following error message:
> ../temporarytest.cpp: In function `int main()':
> ../temporarytest.cpp:12: error: `hidden_copying::hidden_copying(const
> hidden_copying&)' is private
> ../temporarytest.cpp:48: error: within this context
> 
> Without breaking valarray spec (in the above case, amounting to making any of
> the copy constructors of hidden_copying public), how can I get the above code
> work work properly.   If There is no way, than please explain how to
> reconsile behaviors with spec definition of std::slice_array.
> 
> Thank you for your help.
> 
> -     Garrett
>