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RTTI : Base class type name v/s Derived

Posted on 2006-10-24
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Last Modified: 2012-05-05

Hello there,
    Take a look at the code below

#include <stdio.h>
#include <typeinfo>

class Base {
};

class Drv : public Base {
};

void
printType (char* realName, Base* pbase) {
    printf ("\n%s ==> %s\n\n", realName, typeid(pbase).name());
}

int
main(){
    printType("base", new Base());
    printType("drv", new Drv());
    return 0;
}


If you run it (w/msdev) you'll get the following output

base ==> class Base *
drv ==> class Base *

Apparently, the typeinfo contains the info about the local variable of printType() function.
Is it possible to get the type info of the actual object  instead ?

Something like this:

base ==> class Base *
drv ==> class Drv *

thanks
~J
0
Comment
Question by:mxjijo
  • 4
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6 Comments
 
LVL 17

Accepted Solution

by:
rstaveley earned 200 total points
ID: 17800423
You need to dereference the pointer because you want the type that's pointed to. You will need a virtual function in the base class too to enable polymorphism. Also compile with /GR to enable RTTI.

--------8<--------
#include <stdio.h>
#include <typeinfo>

class Base {
public:
virtual ~Base() {}
};

class Drv : public Base {
};

void
printType (char* realName, Base* pbase) {
    printf ("\n%s ==> %s\n\n", realName, typeid(*pbase).name());
}

int
main(){
    printType("base", new Base());
    printType("drv", new Drv());
    return 0;
}
--------8<--------
0
 
LVL 17

Expert Comment

by:rstaveley
ID: 17800453
> #include <stdio.h>

Strictly speaking you should use...

#include <cstdio>

...with C++ too.

If you are relatively new to C++, note that typeid and dynamic_cast<> (the two aspects of RTTI) are seldom used and therefore not worth mastering initially. That's why Microsoft doesn't enable RTTI by default. Good OOP design and getting polymorphism to work for you will make them unnecessary 99.999% of the time.
0
 
LVL 8

Author Comment

by:mxjijo
ID: 17801505
great. that would do.
thanks
0
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LVL 17

Expert Comment

by:rstaveley
ID: 17806700
Hit the accept button to accept the answer, mxjijo. Otherwise, the question remains open.
0
 
LVL 8

Author Comment

by:mxjijo
ID: 17806873

I'm sorry I thought I did :)
0
 
LVL 17

Expert Comment

by:rstaveley
ID: 17806948
Thanks :-)
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