What are the bad habits of C programmers starting to write C++? [closed]

Answer 1

Passing objects with pointers instead of references. Yes, there are still times when you need pointers in C++, but references are safer, so you should use them when you can.

Answer 2

Making everything in a class public. So, data members that should be private aren't.

Answer 3

Not fully understanding the semantics of pointers and references and when to use one or the other. Related to pointers is also the issue of not managing dynamic allocated memory correctly or failing at using "smarter" constructs for that(e.g. smart pointers).

Answer 4

Confused uses of structs vs. classes, overuse of global methods that take object pointers as arguments, and globally-accessible instance pointers, a la:

extern Application* g_pApp;
void RunApplication(Application* app, int flags);

Also (not saying it's totally useless, but still):

const void* buf;

Answer 5

Assuming said programmers have already made the mistake of attempting to learn C++:

Mistakes

• Not using STL.
• Trying to wrap everything in classes.
• Trying to use templates for everything.
• Not using Boost. (I know Boost can be a real PITA, and a learning curve, but C++ is just C+ without it. Boost gives C++ some batteries).
• Not using smart pointers.
• Not using RAII.
• Overusing exceptions.

Controversial

• Moving to C++. Don't do it.
• Try to convert C stdio to iostreams. Iostreams SUX. Don't use it. It's inherently broken. Look here.
• Using the following parts of the libstdc++ library:
  • strings (beyond freeing them for me, go the hell away)
  • localization (what the hell does this have to do with c++, worse yet, it's awful)
  • input/output (64 bit file offsets? heard of them?)
• Naively believing you can still debug on the command line. Don't use C++ extensively without a code crane (IDE).
• Following C++ blogs. C++ blogs carp on about what essentially boils down to metadata and sugar. Beyond a good FAQ, and experience, I've yet to see a useful C++ blog. (Note that's a challenge: I'd love to read a good C++ blog.)

Answer 6

Very experienced developers not understanding casting or even object oriented programming:

I started helping out on a project and one of the senior guys was having a problem with some code that used to work and now didn't.

(Class names have been changed to protect the innocent, and I can't remember the exact names) He had some C++ code that was listening to incoming message classes and reading them. The way it had worked in the past was that a Message class was passed in and he would interogate a variable on it to find out what type of message it was. He would then C-style cast the Message as another specialised class he'd written that inherited from Message. This new class had functions on it that extracted the data how he wanted it. Now, this had been working for him fine but now was not.

After many hours looking through his code he could not see a problem and I had a look over his shoulder. Immediately I told him that it's not a good idea to C-style cast Message to a derived class which it was not. He disagreed with me and said he'd been doing it for years and if that was wrong then everything he does is wrong because he frequently uses this approach. He was further backed up by a contractor who told me I was wrong. They both argued that this always works and the code hasn't changed so it's not this approach but something else that has broken his code.

I looked a bit further and found the difference. The latest version of the Message class had a virtual function and hadn't previously had any use of virtual. I told the pair of them that there was now a virtual table and functions were being looked up, etc, etc.... and this was causing their problem, etc, etc.... They eventually agreed and I was presented with a comment that I will never forget: "Virtual completely screws up polymorphism and object oriented programming".

I forwarded them a copy of a decorator pattern as an example of how to add a function to an existing class but heard nothing back from them. How they fixed the idea I have no idea.