What are the often misunderstood concepts in C++? [closed]

Question

C++ is not C with classes!

And there is no language called C/C++. Everything goes downhill from there.

That C++ does have automatic resource management.

(Most people who claim that C++ does not have memory management try to use new and delete way too much, not realising that if they allowed C++ to manage the resource themselves, the task gets much easier).

Example: (Made with a made up API because I do not have time to check the docs now)

// C++
void DoSomething()
{
  File file("/tmp/dosomething", "rb");
  ... do stuff with file...
  // file is automatically free'ed and closed.
}

// C#
public void DoSomething()
{
  File file = new File("/tmp/dosomething", "rb");
  ... do stuff with file...

  // file is NOT automatically closed.
  // What if the caller calls DoSomething() in a tight loop?
  // C# requires you to be aware of the implementation of the File class
  // and forces you to accommodate, thus voiding implementation-hiding
  // principles.
  // Approaches may include:
  // 1) Utilizing the IDisposable pattern.
  // 2) Utilizing try-finally guards, which quickly gets messy.
  // 3) The nagging doubt that you've forgotten something /somewhere/ in your
  //    1 million loc project.
  // 4) The realization that point #3 can not be fixed by fixing the File
  //    class.
}

Free functions are not bad just because they are not within a class C++ is not an OOP language alone, but builds upon a whole stack of techniques.

I've heard it many times when people say free functions (those in namespaces and global namespace) are a "relict of C times" and should be avoided. Quite the opposite is true. Free functions allow to decouple functions from specific classes and allow reuse of functionality. It's also recommended to use free functions instead of member functions if the function don't need access to implementation details - because this will eliminate cascading changes when one changes the implementation of a class among other advantages.

This is also reflected in the language: The range-based for loop in C++0x (next C++ version released very soon) will be based on free function calls. It will get begin / end iterators by calling the free functions begin and end.

The difference between assignment and initialisation:

string s = "foo";    // initialisation
s = "bar";           // assignment

Initialisation always uses constructors, assignment always uses operator=

In decreasing order:

1. make sure to release pointers for allocated memory
2. when destructors should be virtual
3. how virtual functions work

Interestingly not many people know the full details of virtual functions, but still seem to be ok with getting work done.

The most pernicious concept I've seen is that it should be treated as C with some addons. In fact, with modern C++ systems, it should be treated as a different language, and most of the C++-bashing I see is based on the "C with add-ons" model.

To mention some issues:

While you probably need to know the difference between delete and delete[], you should normally be writing neither. Use smart pointers and std::vector<>.

In fact, you should be using a * only rarely. Use std::string for strings. (Yes, it's badly designed. Use it anyway.)

RAII means you don't generally have to write clean-up code. Clean-up code is bad style, and destroys conceptual locality. As a bonus, using RAII (including smart pointers) gives you a lot of basic exception safety for free. Overall, it's much better than garbage collection in some ways.

In general, class data members shouldn't be directly visible, either by being public or by having getters and setters. There are exceptions (such as x and y in a point class), but they are exceptions, and should be considered as such.

And the big one: there is no such language as C/C++. It is possible to write programs that can compile properly under either language, but such programs are not good C++ and are not normally good C. The languages have been diverging since Stroustrup started working on "C with Classes", and are less similar now than ever. Using "C/C++" as a language name is prima facie evidence that the user doesn't know what he or she is talking about. C++, properly used, is no more like C than Java or C# are.