Re: casting from void*

From:

s0suk3@gmail.com

Newsgroups:

comp.lang.c++

Date:

Tue, 11 Sep 2012 08:27:24 -0700 (PDT)

Message-ID:

<81db1bd8-7649-43df-98a0-5d90ce02565e@googlegroups.com>

On Tuesday, September 11, 2012 6:15:19 AM UTC-5, Cristiano wrote:

I have a structure like this (the actual structure is much bigger):

struct Generic {

    char ID[6];

    std::vector <obj1_info> info1;

    std::vector <obj2_info> info2;

    std::vector <obj3_info> info3;

    std::vector <obj4_info> info4;

};

I use it to store 4 types of objects.

Each object needs its own std::vector to store informations related to

that object.

To avoid wasting of space I though to use a void * instead:

struct Generic {

    char ID[6];

    void *ptr;

};

Not a good idea, I know.

First question: does anybody have a good idea?

You can create an abstract base class that's conceptually an interface and have all the info's implement it:

class ObjectInfo
{
public:
    virtual Xyz GetXyz() const = 0;
    virtual Zyx GetZyx() const = 0;
};

class Object1Info : public ObjectInfo { ... };
class Object2Info : public ObjectInfo { ... };

And the vector in Generic will store ObjectInfo pointers:

struct Generic
{
    char ID[6];
    std::vector<ObjectInfo*> info; // or maybe vector<shared_ptr<ObjectInfo>>
};

Then you can add any kind of ObjectInfo to the vector:

Object1Info* x = new Object1Info();
x->var = 0;
info.push_back(x);

Although this saves space (for the vectors), it introduces more dynamic allocations, and I'm not sure what's the space overhead of the virtual methods.