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dynamic instantiation of c++ objects

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Join Date: Nov 2009

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Reputation: manoj.pg is an unknown quantity at this point

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manoj.pg

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dynamic instantiation of c++ objects

25 Days Ago

If I have the class name in a string varibale, how can I instantiate an object of that class?

I am just thinking of COM and CORBA implementations where C++ object is instantiated from the data in the stream. How can I implement it?

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Join Date: Aug 2005

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iamthwee

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Posting Expert

25 Days Ago

You mean something like?

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <iostream>
#include <string>
 
class Foo
{
public:
       std::string sayHello()
       {
         return "Hello";
       }
};
 
int main()
{
    Foo test;
    std::cout << test.sayHello();
 
    std::cin.get();
}
#include <iostream>
#include <string>

class Foo
{
public:
       std::string sayHello()
       {
         return "Hello";
       }
};

int main()
{
    Foo test;
    std::cout << test.sayHello();
    
    std::cin.get();
}

*Voted best profile in the world*

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Join Date: Sep 2009

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Reputation: jonsca is an unknown quantity at this point

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jonsca

Online

Posting Whiz

25 Days Ago

I think he might mean a situation where you could take in a class name from the user and instantiate a class, so in your example above:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
string classname;
std::cin >> classname;
(it's invalid but...)  classname * cn = new classname();
 
string classname;
std::cin >> classname;
(it's invalid but...)  classname * cn = new classname();

I think for a finite number of cases you could use a bunch of if/else if statements:

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 C++ Syntax (Toggle Plain Text) 
if(classname == "Foo")
     Foo * foo = new Foo();
elseif(classname  == "Bar")
     Bar * bar = new Bar();
...
if(classname == "Foo")
     Foo * foo = new Foo();
elseif(classname  == "Bar")
     Bar * bar = new Bar();
...

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Join Date: Dec 2008

Posts: 1,151

Reputation: firstPerson is just really nice

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firstPerson firstPerson is offline

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Veteran Poster

25 Days Ago

>>If I have the class name in a string varibale, how can I instantiate an object of that class?

Your question is not very clear, but my guess would be that you meant
something like :

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
class Foo
{
   public Foo() { }
};
 
int main()
{
    string className = "Foo";
    Foo * foo; //not instantiated but waiting in a sense to be created.
 
    if( className == "Foo")  //a string variable has the class name FO
       foo = new Foo(); //so create a new class of that object
 
   //after foo is done being used with
  delete foo;
}
class Foo
{
   public Foo() { }
};

int main()
{
    string className = "Foo";
    Foo * foo; //not instantiated but waiting in a sense to be created.

    if( className == "Foo")  //a string variable has the class name FO
       foo = new Foo(); //so create a new class of that object

   //after foo is done being used with
  delete foo;
}

Last edited by firstPerson; 25 Days Ago at 2:30 pm.

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