Question

I’m currently learning C++ and trying to get used to the standard data structures that come with it, but they all seem very bare. For example, list doesn’t have simple accessors like get(index) that I’m used to in Java. Methods like pop_back and pop_front don’t return the object in the list either. So you have to do something like:

Object blah = myList.back();
myList.pop_back();

Instead of something simple like:
Object blah = myList.pop_back();

In Java, just about every data structure returns the object back so you don’t have to make these extra calls. Why is the STL containers for C++ designed like this? Are common operations like this that I do in Java not so common for C++?

edit: Sorry, I guess my question was worded very poorly to get all these downvotes, but surely somebody could have edited it. To clarify, I’m wondering why the STL data structures are created like this in comparison to Java. Or am I using the wrong set of data structures to begin with? My point is that these seem like common operations you might use on (in my example) a list and surely everybody does not want to write their own implementation each time.

edit: reworded the question to be more clear.

Answer 1

Quite a few have already answered the specific points you raised, so I’ll try to take a look for a second at the larger picture.

One of the must fundamental differences between Java and C++ is that C++ works primarily with values, while Java works primarily with references.

For example, if I have something like:

class X {
    // ...
};

// ...
X x;

In Java, x is only a reference to an object of type X. To have an actual object of type X for it to refer to, I normally have something like: X x = new X;. In C++, however, X x;, by itself, defines an object of type X, not just a reference to an object. We can use that object directly, not via a reference (i.e., a pointer in disguise).

Although this may initially seem like a fairly trivial difference, the effects are substantial and pervasive. One effect (probably the most important in this case) is that in Java, returning a value does not involve copying the object itself at all. It just involves copying a reference to the value. This is normally presumed to be extremely inexpensive and (probably more importantly) completely safe — it can never throw an exception.

In C++, you’re dealing directly with values instead. When you return an object, you’re not just returning a reference to the existing object, you’re returning that object’s value, usually in the form of a copy of that object’s state. Of course, it’s also possible to return a reference (or pointer) if you want, but to make that happen, you have to make it explicit.

The standard containers are (if anything) even more heavily oriented toward working with values rather than references. When you add a value to a collection, what gets added is a copy of the value you passed, and when you get something back out, you get a copy of the value that was in the container itself.

Among other things, this means that while returning a value might be cheap and safe just like in Java, it can also be expensive and/or throw an exception. If the programmer wants to store pointers, s/he can certainly do so — but the language doesn’t require it like Java does. Since returning an object can be expensive and/or throw, the containers in the standard library are generally built around ensuring they can work reasonably well if copying is expensive, and (more importantly) work correctly, even when/if copying throws an exception.

This basic difference in design accounts not only for the differences you’ve pointed out, but quite a few more as well.