Re: Checking for null pointer for structure

* GrzybSon:


The design. Sorry, that's brutal, and even though I'm pretty old I've not yet
learned how to say such things in some acceptable way. So I just go for the
straightforward, hoping people will forgive me since the info is good, yes?

Okay, others will probably comment on your char*'s, recommending instead
std::string, but let's look at the design.

As I understand it you want TopStruct to have an optional NestedStruct.

Some TopStruct-s will have a NestedStruct, some will not.

The question is, will any given TopStruct ever /acquire/ or /lose/ a
NestedStruct, or is a TopStruct created with/without a NestedStruct and staying
that way for its lifetime?

If it stays that way for its lifetime, then a natural solution is to use
inheritance.

It then goes like this:

   struct TopStruct
   {
       virtual ~TopStruct() {} // You need /some/ virtual method.
       std::string ggg;
   };

   struct WithNestedStruct: TopStruct // Inheritance
   {
       std::string text;
   };

   ...

   while( (top = GetStructs()) != 0 )
   {
       if( WithNestedStruct* p = dynamic_cast<WithNestedStruct*>( top ) )
       {
           // Do things with p
       }
   }

There are more advanced techniques to avoid the 'if' or 'case', that is, to
avoid explicit type discrimantion, and generally those techniques are based on
using virtual methods. In short, you let the effect of a call to method depend
on the object at hand. But perhaps first try if you can get the above to work,
assuming of course that the assumption of TopStruct-s staying the way they're
created, holds.

If that assumption does not hold, then use a pointer in TopStruct, and then take
care not to copy those structs, or if you do, decide on what to do with pointer.