java - When to use pointers and when not to?

Question

I'm used to doing Java programming, where you never really have to think about pointers when programming. However, at the moment I'm writing a program in C++. When making classes that have members of other classes, when should I use pointers and when should I not? For example, when would I want to do this:

class Foo {
    Bar b;
}

As opposed to this:

class Foo {
    Bar* b;
}

Answer 1

Start by avoiding pointers.

Use them when:

• You want to use the Pimpl idiom, or an abstract factory.
• The Bar instance is actually managed by some other part of your program, whereas the Foo class just needs to be able to access it.
• You want to postpone the construction of the Bar object (i.e., you want to create it after constructing Foo).
• In your business logic, the Bar object may not exist at all; you would use null also in Java. However, check out boost::optional as well.
• Bar is actually a base class, and you need the instance to be polymorphic.
• You happen to be using a toolkit that prefers to present GUI widgets as pointers. Examples could include (but are certainly not limited to) wxWidgets and GLUI.

In any of these cases (*), start by using a smart pointer, such as boost::shared_ptr. Otherwise, you are likely to forget to deallocate the memory, sooner or later. Once you know what you are doing, consider case-by-case what pointer type is best.

(*) any case – except, probably, the bullet regarding GUI widgets; in this case, your toolkit would most probably manage the resources for you as well