instanceof in C++?

[Michael]

Hi All,

Is there a function similar to Java's instanceof in C++?
To ask the question a different way, if I have a base class and two derived
classes, how can I tell which one of the derived classes a particular object
belongs to?

BaseClass* base;

if(some_test){
base = new Class1;
} else {
base = new Class2;
}

How can I tell if I created a Class1 or Class2 object from the object?

Thanks for your help

Michael

 

[m_schellens]

Hi All,

Is there a function similar to Java's instanceof in C++?
To ask the question a different way, if I have a base class and two derived
classes, how can I tell which one of the derived classes a particular object
belongs to?

BaseClass* base;

if(some_test){
base = new Class1;} else {

base = new Class2;

}

How can I tell if I created a Class1 or Class2 object from the object?

Thanks for your help

Michael

dynamic_cast is your friend.

Cheers
Marc

 

[Stefan Naewe]

Hi All,

Is there a function similar to Java's instanceof in C++?
To ask the question a different way, if I have a base class and two derived
classes, how can I tell which one of the derived classes a particular object
belongs to?

BaseClass* base;

if(some_test){
base = new Class1;
} else {
base = new Class2;
}

How can I tell if I created a Class1 or Class2 object from the object?

Use dynamic_cast<> :

if(Class1* c1 = dynamic_cast<Class1*>(base))
// it's a Class1*
else if (Class2* c2 = dynamic_cast<Class2*>(base))
// it's a Class2*


But: Frequent use of dynamic_cast<> is a smell of bad design!


S.

 

[Mike Wahler]

Hi All,

Is there a function similar to Java's instanceof in C++?
To ask the question a different way, if I have a base class and two
derived classes, how can I tell which one of the derived classes a
particular object belongs to?

BaseClass* base;

if(some_test){
base = new Class1;
} else {
base = new Class2;
}

How can I tell if I created a Class1 or Class2 object from the object?

You could use 'dynamic_cast', but the whole point of derivation
(with a reasonable design), is that you should not *need* to know
which derived type it is. From an interface standpoint, both
your instances are type 'base' (Isn't that why you used type 'base*'
with 'new'?). If there were a situation where the derived type is
significant,
I'd think you'd write:

Class1 *c = new Class1;

-Mike