C gotchas and mistakes for C++ programmers

Question

If you are C programmer or C++ programmer that knows C well, can you tell me what are the most common mistakes/pattern/style that you noticed from C++ programmers? For example, do you noticed a difference between a C program written by a C programmer vs C program written by C++ programmer? If you can provide a list specifying the major misunderstandings that C++ programmers tend to have about C, I will really appreciate it.

I want to learn C, but while a C++ background helps, I'm afraid that it might hurt as well. I have this weird assumption that besides some keywords and libraries, I don't have to learn anything else because I know C++. I feel bad about having that assumption because I do recognize that C++ != C, but sometimes the difference get blurry when I use C libraries in C++ or maintained legacy procedural C++ from others.

Btw, I'm not asking what are the C++ features not present in C, or whether we/they use "malloc" and they/we use "new".

Thanks.

You need to go back to previous questions you have answered, look for the most relevant answer and click the checkmark beside it. — GWW, Jun 07 '11 at 17:00

score 3 · Accepted Answer · answered Jun 07 '11 at 16:56

One thing that I see happen quite frequently is properly freeing allocated memory. Especially associated with structures containing dynamically allocated memory. With C++, destructors are automatically called and if properly written they take care of the associated objects clean up. With C you have to remember to either free all the memory allocated with a structure, or remember to call some kind of destruct function that does it for you.

score 1 · Answer 2 · answered Jun 07 '11 at 16:57

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I'm not sure I'd call this a "mistake", but an experienced C++ programmer who has to use C is likely to create a lot of things that look like classes and virtual-function tables.

This is not necessarily a bad thing, as you can certainly do object-oriented programming in C, but it may be overkill for a particular problem.

answered Jun 07 '11 at 16:57

Kristopher Johnson

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"an experienced C++ programmer who has to use C is likely to create a lot of things that look like classes and virtual-function tables." It's funny that you should mention that, as even though I'm not an experienced C++ programmer, I was recently entertaining the idea of implementing a class-like object using a struct containing function pointers for fun. – JAB Jun 07 '11 at 16:59

score 1 · Answer 3 · answered Jun 07 '11 at 16:57

I can't really say from personal experience, but I believe you may potentially encounter some subtle problems with things like references (prepending & to a variable name) as function parameters, how enums aren't fully qualified types like they are in C++, stuff involving memory functions that return void pointers... things like that.

score -1 · Answer 4 · answered Jun 07 '11 at 16:53

-1

Pretty much, when you find idiomatic C code, then it looks similar to idiomatic C++ code, except you have to hack around all the missing language features and implement your own half-assed version of them. For example, macros -> templates/inline functions. void* pointers-> inheritance. function pointers->function objects. exceptions->goto & error codes.

answered Jun 07 '11 at 16:53

Puppy

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Idiomatic C does _not_ look similar to idiomatic C++. – Lightness Races in Orbit Jun 07 '11 at 16:57

C gotchas and mistakes for C++ programmers

4 Answers4

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