Using/Mixing C in C++ code?

Question

Is using C in C++ bad?

Many people have told me that using C in C++ is bad because it's not as safe, and it requires more memory management. I keep telling them that as long as you know what you're doing, and you delete your "new"s and free your "malloc"s then C isn't a problem.

I'm currently on a forum where an argument over std::string vs. a char* is taking place. Some people are saying that allocating a simple char* memory block is more efficient, and as long as you deallocate it, it's fine. On the other hand we have people saying that std::string is superior because it has no memory management involved but is less efficient.

So the main question here is:

• Is mixing C/C++ bad? Should you ONLY use 100% C++ when you're coding C++?

Any answers would be appreciated!

Answer 1

I keep telling them that as long as you know what your doing, and you delete your new's and free your malloc's then C isn't a problem.

This is true; if you are extraordinarily careful and ensure that you manually clean things up, then it isn't a problem. But do you really have the time to do that? Every call to new can throw std::bad_alloc. Do you always catch every exception that can be thrown and manually clean up any resources?

I'd hazard to guess the answer to that is "no," because it is very tedious to write code like that and it is difficult to be absolutely sure that code written like that is correct, even in the case of rare failures.

If the answer is "yes," then why are you wasting so much time worrying about resource management? C++ idioms like scope-bound resource management (SBRM; more commonly known as resource acquisition is initialization (RAII)) and libraries like the standard template library are there to help you write correct code more easily. Why do things the hard way when you don't have to?

Should you ONLY use 100% C++ when your coding C++?

Yes, though if there is a C library that does something you need, or if you have legacy C code that you want to use, you can certainly use that code; just be sure to be careful. Often the cleanest way to interop with C code is to write a C++ wrapper around it.

Answer 2

My strong belief is that your question doesn't have to do with C or C++ at all. Your question is about trading dubious efficiency for safety. Yes, C can be more efficient. But how much more efficient? And what do you pay for that? These are the questions you should answer. In most cases string vs. const char* overhead is unnoticeable. If you are developing an efficiency-extremely-critical application, then why not code it in C in the first place?

Answer 3

I'm genuinely surprised by the polarization in the answers and comments thereof.

In my eyes, the answer is pretty simple:

When writing a C++ project, use C++, avoid C ( and family) and stick to the Standard Library and STL. Ensure a homogenous C++ interface (it is a C++ project after all!) When using an external project in C, which happens to be written in C, of course you can use it. (see examples below)

Two prime examples:

1. Write a C++ program/library that does scientific calculations. I would definitely use GSL (GNU Scientific Library), and it is written in C. There are only a few caveats (like specialized initialize and free functions for specific structs and functions within GSL), that can be absorbed in a std::unique_ptr typedef. There is also the issue of error handling: checking error codes can be abstracted away in an exception mechanism if necessary/wanted, or you can keep the error codes contained within the calculation functions. GSL does have a way of setting up an error handler, I imagine some other C libraries have such a functionality.

2. Writing a C++ program using the Win32 API, which is horribly C based. I'm talking about light API usage, like reading the files in a directory, checking if a file exists, etc., not heavy GDI+ or other stuff. I like to wrap all the C functions the Win32 API exposes in nice C++ style functions, perhaps with the necessary exceptions and returning a std::string instead of having to pass a char* buffer as argument.

I understand both examples are quite... shallow... but I feel they express a general enough idea.

Answer 4

Yes it's bad to mix C and C++, and the reason has nothing to do with performance or security:

It is bad cause of a maintainability:

• a C++ programmer expects all code to behave like C++.
• a C programmer expects all code to behave like C.

So when you mix C++ and C, you break both programmers expectations on how things should work.