question  one vector for two class

akayrak (6)   Link to this post
how to i create a vector that holds two class' type?
firedraco (2048)   Link to this post
Use a vector of std::pair
kevinchkin (363)   Link to this post
May be by creating a class that contains the two class types you want and then creating the vector of that new class?
akayrak (6)   Link to this post
i thınk you mısunderstand me firedraco. I want a vector that;

let's say it's name is "vect". and vect.at(i) can hold integer vect.at(i+1) can hold string.
(any element of vector can hold integer -or- string)

and kevinchkin, how can ı do that. it does not much dıffer from holding two separate vector. right?

thank you for answers.
helios (4790)   Link to this post
Vectors, being arrays, are unable to hold differently-sized elements.
There are two possibilities in this case:
1. Use two vectors, one for each type: std::vector<int>/std::vector<std::string>
2. Use a vector that holds structures, each of which holds both types. std::vector<std::pair<int,std::string> > (note the space between the greater-than symbols. It's mandatory)
Abramus (36)   Link to this post
I don't know details of your program, but you may try to use a vector of pointers to some base class. Object stored in the vector should be of types derived from this base class. Additionally you may use some kind of smart pointer to make memory management easier (std::auto_ptr cannot be used since it does not have a proper = operator).

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template <typename T_base>
class smart_pointer_t
{
public:

   template <typename T_derived>
   smart_pointer_t(T_derived * ptr_) : ptr(ptr_){}

   ~smart_pointer_t(){ delete ptr; }

   ...

private:

   T_base * ptr;
};

class base_t
{
   ...
};

class derived_1_t : public base_t
{
   ...
};

class derived_2_t : public base_t
{
   ...
};

int main()
{
   std::vector<smart_pointer_t<base_t> > table;

   table.push_back(smart_pointer_t(new derived_1_t));
   table.push_back(smart_pointer_t(new derived_2_t));

   return 0;
}
jsmith (3099)   Link to this post
Other options are

  
std::vector< boost::variant< type-1, type-2, ... > >


If you know the types at compile time and there are only a couple of them (by default variant supports up to 9
different types, IIRC).

Or

  
std::vector< boost::any >


If you only know the types at runtime, but then it becomes a bit of a problem extracting values, since in order
to get the value out of a boost::any you must any_cast<> it to the correct type. (If you get the type wrong,
any_cast will throw if casting to reference or return NULL if casting to pointer).

kevinchkin (363)   Link to this post
how can ı do that. it does not much dıffer from holding two separate vector. right?


I guess pair is better way to go. I didn't know about it. But anyways what I was saying that you can do something like:

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class  A { 

   public:
      int a; 
} ; 

class B { 
    public:
         int b ; 
} ; 

class C { 
     public: 
        A Obj1 ; 
        B Obj2 ; 
} ;  

int main( ){ 
  vector<C> myVec; 
  return 0 ; 
}
wasabi (18)   Link to this post
Or as kevinchkin said before, just make a vector of a class that contains an integer and a string.

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class A {
int a;
char* b;
};


You can then make an array of said class, where vect[i].a is an integer and vect[i].b is a string.
helios (4790)   Link to this post
kevinchkin: What would you gain from doing something like that? I mean, what's the purpose of A and B? Why not just put their members in C?
kevinchkin (363)   Link to this post
@helios: I will not gain anything. :-)
The OP mentioned that he wanted vector to hold two classes that's why I just showed an example.

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