How could I cast to a variable class name?

Question

I have some classes and a pointer, which class is void*, pointing to one of these classes.

I also have the name of that class in a string variable and I would like to cast that void pointer to that class.

I would like to do something like that:

    string className;

    className = "int";

    (className *) voidPointer;

is there any way to do that??

thank you in advance!

Possible Duplicate http://stackoverflow.com/questions/582331/is-there-a-way-to-instantiate-objects-from-a-string-holding-their-class-name — Joe, Dec 09 '11 at 15:26
C++ is a statically typed language. If you want to do this, you will have to implement your own scheme. The question Joe suggested as a dupe has a few ideas. Voted to close this one. — sbi, Dec 09 '11 at 15:31

Nawaz · Answer 1 · 2011-12-09T15:36:29.640

That is not possible the way you're trying to do.

However, I think boost::any can help you here:

boost::any obj;
if (className == "int")
   obj = (int)voidPointer;
else if (className == "short")
   obj = (short)voidPointer;

//from now you can call obj.type() to know the type of value obj holds
//for example
if(obj.type() == typeid(int))
{
    int value = boost::any_cast<int>(obj);
    std::cout <<"Stored value is int = " << value << std::endl;
}

That is, use boost::any_cast to get the value stored in object of boost::any type.

score 1 · Answer 2 · answered Dec 09 '11 at 15:26

C++ doesn't have reflection so you cannot do this easily.

What you can do is something on these lines

string classname;
void * ptr;

if ( classname == "Foo" )
{
    Foo* f = static_cast<Foo*> ( ptr );
}
else if ( classname == "Bar" )
{
    Bar* f = static_cast<Bar*> ( ptr );
}

score 0 · Answer 3 · answered Dec 09 '11 at 15:27

0

No, you cannot do this. However, you could conceivably use a template class to do this. Note I am providing a solution, but I don't think you should be storing a void* pointer anyway.

template<class T>
T* cast(void* ptr) { return static_cast<T*>(ptr); };

Then, you can do:

int* intPtr = cast<int>(ptr);

I repeat, you probably don't need to be using void* at all.

answered Dec 09 '11 at 15:27

Moo-Juice

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The OP has classnames stored in string. Your solution doesn't cover it – parapura rajkumar Dec 09 '11 at 15:32
I am aware of what was in the OP. I don't think he should be doing it at all, but unfortunately we only get a snippet of the over-all problem. Perhaps he wants to cast based on some other "type of" field he has. Perhaps he wants to store different types in a property-type collection. You get my drift? – Moo-Juice Dec 09 '11 at 15:35

score 0 · Answer 4 · answered Dec 09 '11 at 15:29

0

Sure you can do that:

if (className == "int") {
  int *intPtr = static_cast<int*>(voidPointer);
}

This is not very elegant, though - but you can certainly do that if you must (but there is most probably a better solution to your problem).

answered Dec 09 '11 at 15:29

cli_hlt

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How could I cast to a variable class name?

4 Answers4