about the pointer array using template in c++

Question

i have a class shown below:

template <class TValue>
    class ICData
    {
    private :
TValue value;
    public:
inline ICData()
{
};
TValue get_value();
void set_value(TValue data);
    };

    template <class TValue>
    TValue ICData<TValue>::get_value()
    {
return value;
    }

     template <class TValue>
     void ICData<TValue>::set_value(TValue _value)
     {
value=_value;
     }

i know how to make a pointer array by:

    ICData <int> *ICArray[10];
    ICArray[0]=new ICData<int>();
    ICArray[1]=new ICData<int>();

but is there any way to make a pointer array using template ? like below:

            template <class T>// iknow this code is WRONG
    ICData <T> *ICArray[10];
    ICArray[0]=new ICData<int>();
    ICArray[1]=new ICData<float>();

thanks in advance.

You mean a template declaration? Templates are for type redefinitions, but you need to supply the template value at some point. — oh whatever
– oh whatever, Commented Dec 27, 2011 at 8:50
i know that i should supply it some where : ICArray[0]=new ICData<int>(); — mefmef
– mefmef, Commented Dec 27, 2011 at 8:55
i wonder how do you intend to use ICData <T> *ICArray[10];? — Donotalo
– Donotalo, Commented Dec 27, 2011 at 8:55
@Donotalo look at the difference : ICArray[0]=new ICData<int>(); ICArray[1]=new ICData<float>(); — mefmef
– mefmef, Commented Dec 27, 2011 at 8:57

Lara Bailey · Accepted Answer · 2011-12-27 09:03:28Z

1

If you wanted to store a pointer that could point to either a ICData<int> or a ICData<float> then those types would have to have a common base class and you could use that common base as the type to point to.

As it stands the type ICData<int> and ICData<float> are not related so other than using void * there is no solution to what you want to do that wouldn't involve some ugly casts.

answered Dec 27, 2011 at 9:03

Lara Bailey

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4 Comments

mefmef Over a year ago

void *ICArray[10]; ICArray[0]=new ICData<int>(ln); ICArray[1]=new ICData<float>(ln2); this code works but how can i access ICArray[0].get_Value()?

Lara Bailey Over a year ago

@mefmef: You have to cast it back to the correct type first. e.g. static_cast< ICData<int>& >(ICArray[0]).get_Value()

mefmef Over a year ago

:Error 15 error C2440: 'static_cast' : cannot convert from 'void *' to 'ICData<TValue> &' c:\documents and settings\h.farazi\my documents\visual studio 2010\projects\icarraytest\main.cpp 22 1 ICArrayTest

Lara Bailey Over a year ago

@mefmef: Sorry, my mistake, I meant: static_cast< ICData<int>* >(ICArray[0])->get_Value(). I'm not sure why you are getting TValue in the error message, though.

Sjoerd · Accepted Answer · 2011-12-27 09:08:20Z

1

You cannot use this approach to store both ICData<int> and ICData<float> in the same ICArray.

It could be made to work, if you derive ICData<T> from a non-templatized ICDataBase, and use ICDataBase* ICArray[10]. However, the static type will be lost so most likely (you would want to use the stored value at some point, won't you?) this will lead to a lot of casting.

Another option is to use boost::any.

However, usually there is a better approach without using boost::any (although it is justified in some cases). So I would suggest to take a step back and rethink your solution.

answered Dec 27, 2011 at 9:08

Sjoerd

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