About uncopyable class (on book:Effective C++) Post: 302738345

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Top Forums Programming About uncopyable class (on book:Effective C++) Post 302738345 by vistastar on Saturday 1st of December 2012 05:20:13 AM

12-01-2012

Registered User

About uncopyable class (on book:Effective C++)

See the following code:

Code:

#include<iostream>
using namespace std;
class Uncopyable
{
protected:
    Uncopyable(){cout<<"hehe\n";}
    ~Uncopyable(){}
private:
    Uncopyable(const Uncopyable &rhs){cout<<"oooops\n";};
    Uncopyable& operator=(const Uncopyable &rhs);
};

class Dog : private Uncopyable
{
    string name;
    int value;
public:

    Dog(const string &s, const int &v):name(s), value(v){}
public:
    //Dog(const Dog &rhs){};             //here is the question!
};

int main()
{
    Dog a("a", 9);
    Dog b(a);
}

If I comment out that line, g++ will complaint "Uncopyable::Uncopyable(const Uncopyable&) is private". I think that mean the default copy ctor of derived class created by g++ called the base class' copy ctor.

If I make available of that line, every thing is ok. It out put

Code:

hehe
hehe

I think this mean the default copy ctor of derived class created by g++ called the base class' default ctor.
Am I right? If yes, why doesn't the default copy ctor derived class, in condition 2, call the base class' copy ctor? Why it behave so inconsistently?

thank you!

Last edited by vistastar; 12-01-2012 at 06:31 AM..

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LEARN ABOUT OSX

is

is(n)								    [incr Tcl]								     is(n)

__________________________________________________________________________________________________________________________________________________

NAME

       is - test argument to see if it is a class or an object

SYNOPSIS

       itcl::is option ?arg arg ...?
_________________________________________________________________

DESCRIPTION

       The is command is used to check if the argument given is a class or an object; depending on the option given. If the argument if a class or
       object, then 1 is returned. Otherwise, 0 is returned.  The is command also recognizes the commands wrapped in the itcl code command.

       The option argument determines what action is carried out by the command.  The legal options (which may be abbreviated) are:

       is class command
	      Returns 1 if command is a class, and returns 0 otherwise.

	      The fully qualified name of the class needs to be given as the command argument. So, if a class resides in  a  namespace,  then  the
	      namespace needs to be specified as well. So, if a class C resides in a namespace N, then the command should be called like:
	      is N::C
		  or
	      is ::N::C

       is object ?-class className? command
	      Returns 1 if command is an object, and returns 0 otherwise.

	      If  the  optional "-class" parameter is specified, then the command will be checked within the context of the class given. Note that
	      className has to exist. If not, then an error will be given. So, if className is uncertain to be a class, then the  programmer  will
	      need to check it's existance beforehand, or wrap it in a catch statement.

	      So, if c is an object in the class C, in namespace N then these are the possibilities (all return 1):
	      set obj [N::C c]
	      itcl::is object N::c
	      itcl::is object c
	      itcl::is object $obj
	      itcl::is object [itcl::code c]

KEYWORDS

       class, object

itcl									3.3								     is(n)

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