prevent accidental object copying in C++

Question

In our company's coding standard, we have been told to "be aware of the ways (accidental) copying can be prevented".

I am not really sure what this means, but assume that they mean we should stop classes from being copied if this is not required.

What I can think of is as follows:

1. Make the copy constructor of a class private.
2. Make the assignment operator (operator=) of a class private.
3. Make the constructor of a class explicit (to stop classes from being created using incorrect variables).
4. For all classes that carry out memory allocation and where copying is required, make sure that the copy constructor and assignment operator carry out deep copying rather than shallow copying.

Am I on the right track? Is there anything I might have missed out?

Answer 1

Yes, making assignment operator and copy constructor private will prevent you from creating any copy of object using standart methods (but if you really need a copy of an object you can implement, for example, Copy() method, which will perform deep copy).

Take a look on boost::noncopyable.

Update (re to Tal Pressman):

...you should be aware of these things and watch out that you don't accidentally copy objects you're not supposed to.

Well, I presume, that any accidental copy will be performed using either assignment operator or copy constructor. So making them private actually makes sense: if object copying is costly operation, then copying must be explicit: other developer can unintentionally indirectly call copy op and compiler will inform him, that this is forbidden.

Answer 2

If your coding standard states "be aware of the ways (accidental) copying can be prevented", I'm guessing they aren't just talking about preventing copies from within the classes itself, but about the performance implications of unnecessary / accidental copies when using the classes.

One of the main causes of unnecessarily wasted performance in the code of people new to C++ is unnecessary copying, usually through temporaries. Compilers are getting better and better at deciding when temporaries are not necessary (see "Want speed? Pass by Value", thanks to Konrad's comment), but the best thing to do is to learn to be aware of the inner workings of copying and temporaries in C++ (among others). For me, reading Efficient C++ really got me started.