How does this work without instantiating an object of the Studentclass?

[amit.bolakani.technical]

#include <iostream>
using namespace std;

class Person{
public:
virtual void print () { cout << "In parent" << endl; }
void onlyInPerson() { cout << "Only in Person/parent" <<
endl; }
};

class Student: public Person{
public:
Student() { cout << "Student constructor." << endl; }
void print() { cout << "In child" << endl; }
void onlyInChild() { cout << "Only in Child/Student" <<
endl; }
};

int main()
{
Person* p ;
Student* s;
s->onlyInChild( );
return 0;
}

[siddhu]

On Dec 14, 4:29 pm, amit.bolakani.t echni...@gmail. com wrote:

#include <iostream>
using namespace std;

class Person{
public:
virtual void print () { cout << "In parent" << endl; }
void onlyInPerson() { cout << "Only in Person/parent" <<
endl; }

};

class Student: public Person{
public:
Student() { cout << "Student constructor." << endl; }
void print() { cout << "In child" << endl; }
void onlyInChild() { cout << "Only in Child/Student" <<
endl; }

};

int main()
{
Person* p ;
Student* s;
s->onlyInChild( );
return 0;

}- Hide quoted text -

- Show quoted text -

Although function is getting called, But its undefined behavior.

[=?utf-8?Q?David_C=C3=B4me?=]

On Fri, 14 Dec 2007 22:29:32 +0100, <am************ *********@gmail .com>
wrote:

#include <iostream>
using namespace std;

class Person{
public:
virtual void print () { cout << "In parent" << endl; }
void onlyInPerson() { cout << "Only in Person/parent" <<
endl; }
};

class Student: public Person{
public:
Student() { cout << "Student constructor." << endl; }
void print() { cout << "In child" << endl; }
void onlyInChild() { cout << "Only in Child/Student" <<
endl; }
};

int main()
{
Person* p ;
Student* s;
s->onlyInChild( );
return 0;
}

I'm not sure but for me it's an undefined behaviour

[amit.bolakani.technical]

On Dec 14, 4:34 pm, David Côme <davidc...@wana doo.frwrote:

On Fri, 14 Dec 2007 22:29:32 +0100, <amit.bolakani. techni...@gmail .com>
wrote:

#include <iostream>
using namespace std;

class Person{
public:
virtual void print () { cout << "In parent" << endl; }
void onlyInPerson() { cout << "Only in Person/parent" <<
endl; }
};

class Student: public Person{
public:
Student() { cout << "Student constructor." << endl; }
void print() { cout << "In child" << endl; }
void onlyInChild() { cout << "Only in Child/Student" <<
endl; }
};

int main()
{
Person* p ;
Student* s;
s->onlyInChild( );
return 0;
}

I'm not sure but for me it's an undefined behaviour

It seems to compile and run fine! I'm pretty surprised and it throws
me off a bit in terms of how it runs fine?

[amit.bolakani.technical]

On Dec 14, 4:45 pm, amit.bolakani.t echni...@gmail. com wrote:

On Dec 14, 4:34 pm, David Côme <davidc...@wana doo.frwrote:

On Fri, 14 Dec 2007 22:29:32 +0100, <amit.bolakani. techni...@gmail .com>
wrote:

#include <iostream>
using namespace std;

class Person{
public:
virtual void print () { cout << "In parent" << endl; }
void onlyInPerson() { cout << "Only in Person/parent" <<
endl; }
};

class Student: public Person{
public:
Student() { cout << "Student constructor." << endl; }
void print() { cout << "In child" << endl; }
void onlyInChild() { cout << "Only in Child/Student" <<
endl; }
};

int main()
{
Person* p ;
Student* s;
s->onlyInChild( );
return 0;
}

I'm not sure but for me it's an undefined behaviour

It seems to compile and run fine! I'm pretty surprised and it throws
me off a bit in terms of how it runs fine?

Did any of you guys try this with your compiler. I tried it with g++
3.4.4 on cygwin.

[Default User]

am************* ********@gmail. com wrote:

int main()
{
Person* p ;
Student* s;
s->onlyInChild( );
return 0;
}

It's Undefined Behavior to deference an invalid pointer. There is no
defined behavior for Undefined Behavior. It is not a syntax error. It
is not a constraint violation. There is no required diagnostic.


Brian

[tragomaskhalos]

On 14 Dec, 21:45, amit.bolakani.t echni...@gmail. com wrote:

On Dec 14, 4:34 pm, David Côme <davidc...@wana doo.frwrote:

On Fri, 14 Dec 2007 22:29:32 +0100, <amit.bolakani. techni...@gmail .com>
wrote:

#include <iostream>
using namespace std;

class Person{
public:
virtual void print () { cout << "In parent" << endl; }
void onlyInPerson() { cout << "Only in Person/parent" <<
endl; }
};

class Student: public Person{
public:
Student() { cout << "Student constructor." << endl; }
void print() { cout << "In child" << endl; }
void onlyInChild() { cout << "Only in Child/Student" <<
endl; }
};

int main()
{
Person* p ;
Student* s;
s->onlyInChild( );
return 0;
}

I'm not sure but for me it's an undefined behaviour

It seems to compile and run fine! I'm pretty surprised and it throws
me off a bit in terms of how it runs fine?- Hide quoted text -

That it happens to work is no surprise - onlyInChild does not access
any members, and the method is not virtual, hence the garbage this
pointer is
not dereferenced. Neverthless it's still undefined behaviour.

[amit.bolakani.technical]

On Dec 14, 4:59 pm, tragomaskhalos <dave.du.verg.. [e-mail] >
wrote:

On 14 Dec, 21:45, amit.bolakani.t echni...@gmail. com wrote:

On Dec 14, 4:34 pm, David Côme <davidc...@wana doo.frwrote:

On Fri, 14 Dec 2007 22:29:32 +0100, <amit.bolakani. techni...@gmail .com>
wrote:

#include <iostream>
using namespace std;

class Person{
public:
virtual void print () { cout << "In parent" << endl; }
void onlyInPerson() { cout << "Only in Person/parent" <<
endl; }
};

class Student: public Person{
public:
Student() { cout << "Student constructor." << endl; }
void print() { cout << "In child" << endl; }
void onlyInChild() { cout << "Only in Child/Student" <<
endl; }
};

int main()
{
Person* p ;
Student* s;
s->onlyInChild( );
return 0;
}

I'm not sure but for me it's an undefined behaviour

It seems to compile and run fine! I'm pretty surprised and it throws
me off a bit in terms of how it runs fine?- Hide quoted text -

That it happens to work is no surprise - onlyInChild does not access
any members, and the method is not virtual, hence the garbage this
pointer is
not dereferenced. Neverthless it's still undefined behaviour.

Isin't the garbage this pointer dereferenced to to call the member
function onlyInChild() ?

[Vaclav Haisman]

am************* ********@gmail. com wrote, On 14.12.2007 22:29:

#include <iostream>
using namespace std;

class Person{
public:
virtual void print () { cout << "In parent" << endl; }
void onlyInPerson() { cout << "Only in Person/parent" <<
endl; }
};

class Student: public Person{
public:
Student() { cout << "Student constructor." << endl; }
void print() { cout << "In child" << endl; }
void onlyInChild() { cout << "Only in Child/Student" <<
endl; }
};

int main()
{
Person* p ;
Student* s;
s->onlyInChild( );
return 0;
}

The programme compiles because it is well-formed and probably even runs
because the methods actually do not touch anything in the object itself but
your programme is invoking undefined behaviour.

--
VH

[amit.bolakani.technical]

On Dec 14, 5:05 pm, Vaclav Haisman <v.hais...@sh.c vut.czwrote:

amit.bolakani.t echni...@gmail. com wrote, On 14.12.2007 22:29:

#include <iostream>
using namespace std;

class Person{
public:
virtual void print () { cout << "In parent" << endl; }
void onlyInPerson() { cout << "Only in Person/parent" <<
endl; }
};

class Student: public Person{
public:
Student() { cout << "Student constructor." << endl; }
void print() { cout << "In child" << endl; }
void onlyInChild() { cout << "Only in Child/Student" <<
endl; }
};

int main()
{
Person* p ;
Student* s;
s->onlyInChild( );
return 0;
}

The programme compiles because it is well-formed and probably even runs
because the methods actually do not touch anything in the object itself but
your programme is invoking undefined behaviour.

--
VH

Ok, so I understand that its undefined behavior. However, is the
garbage this pointer dereferenced to call the member method?