Re: delete map elements

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Sat, 17 Mar 2007 11:32:41 -0400

Message-ID:

<6-OdnQVBE-OMl2HYnZ2dnUVZ_uqvnZ2d@comcast.com>

David wrote:

I try to use map container and delete the elements. but there are
something wrong, please help me check it.

class test{
protected:
      map<string,myclass*> tests;

public:
    test();
    void AddMyclass(const string& myname,const myclass &st);

What's the implementation of it? What do you do with 'st'? The
only allowed thing here is a copy-construction in the free store:

   ...
    tests.insert(make_pair(myname, new myclass(st)));
   ...

   ~test();
};

suppose myclass has been defined before.

and
   test::~test()
   {
      map<string,myclass*>::iterator ii;
     for(ii=tests.begin();ii!=tests.end();++ii)
    {
       delete(ii->second);

You are only allowed to use 'delete' with a pointer you obtained
by using 'new'. Did you?

}
tests.clear();

No need to call 'clear'. The map is going to be destroyed anyway.

  }
int main()
{
   test my;
   myclass st;
   my.AddMyclass("new class",st);
}
But when the code exits from the main function, there was an error
message saying that "Object reference not set to an instance of an
object.".

I think it is caused by the test's destructor function. But I don't
know where is the problem. Please help me. Thanks

You have not shown us the *complete* program. Read FAQ 5.8. The
error is logical, most likely. If you just try to store the _address_
of the local 'st' object, you are not allowed to use 'delete' on it.

V
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