C++ n00b needs help

[R4ZOR]

Hello!

Please help me to understand c++ better:
If I have a class ClassA, and a class named ClassB, which is derived from ClassA.
If I have a function:

Code (cpp) Select Expand

int f(ClassA x) {}
can I pass a variable of type ClassB to this function?

Code (cpp) Select Expand

ClassB b = new ClassB;
f(b);

Thnaks in advance:
R4ZOR

[guest]

use references or pointers

[R4ZOR]

How do you mean that?

[David Perfors]

Code Select Expand

int f(ClassA* x) {}

ClassB b = new ClassB();
f(&b);

I think he is meaning this, I am not sure if this will work.. You have to try
For me programming is always trying.. That's because one thing works for C++ but not for Java or C#...

[gkuznets]

first of all not

Code (cpp) Select Expand

ClassB b = new ClassB;
but

Code (cpp) Select Expand

ClassB* b = new ClassB;

secondly of course you can write

Code (cpp) Select Expand


f(ClassA x) {}
ClassB* b = new ClassB;
f(*b);

and your compiler will interpret this in the following way:

Code (cpp) Select Expand


f((ClassA)(*b)); // TYPECASTING!!!

And inside f will be called member functions of CalssA even if they are overrided in ClassB.

thridly (MAIN SURPRISE)
all changes applyed to x inside f(ClassA x) will not have effect on b!
declaration f(ClassA x) means that inside f will be passed temporarry copy of object *b, which is to be destroyed after exiting from f.
Try to read some books on c++ and start from passing arguments to functions.
(Excuse my poor english)

[thomas]

This is not a "how to learn C++" forum or FAQ, sorry. There are plenty of sites on the web that deal with such things.

You may for example want to read http://www.parashift.com/c++-faq-lite/basics-of-inheritance.html

[enex]

A Crash Course in C++
http://media.wiley.com/product_data/excerpt/41/07645748/0764574841.pdf

Pretty good if you are already familiar with other OO languages like Java.. etc