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I wanted to know how widely used is the mixing of C++ and C. I mean as in using of C libraries/functions and call it in C++ program like how it is done here Mix C with C++. How extensive is its use in real world? Is it rarely used, avoided mostly or pretty common? Anybody can shed some lights on it??

Anzo Sasuke
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    Technically its ubiquitous. Both Windows and *nix use a C API for interacting with the OS. – NathanOliver Aug 19 '21 at 16:29
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    A significant number of libraries is written in C. You don't want to miss on them to maintain the "C++ purity". – HolyBlackCat Aug 19 '21 at 16:29
  • Implementations of the C++ standard library itself will often [mix C libraries](https://en.cppreference.com/w/cpp/header/cstring). It's not required, but it's a fairly easy way to implement "things from C". – Drew Dormann Aug 19 '21 at 16:32
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    Even when writing mostly C++ projects (targeting windows) I very often have at least a few C files, mostly tool generated but not always. – SoronelHaetir Aug 19 '21 at 16:45
  • If I am not wrong, pretty much the whole Arduino/microcontroller programming situation is like that – Giorgos Xou Aug 19 '21 at 17:08
  • Since C++ was originally introduced as an extended or enhanced C, a lot of C programmers claimed they were C++ programmers, based on using techniques from C and a few C++ features. Quite a few courses still teach C++ that way. So a lot of programmers write code that is mostly C but using a few specific features of C++. – Peter Aug 19 '21 at 17:20

1 Answers1

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It is fairly common. You can either

or

  • use both object files, static and dynamic libraries compiled with C compiler but then you should be aware of name mangling that C++ compiler does and the C compiler does not (due to the fact that C does not allow name overloading but C++ does). In such case there is extern "C" linker directive to use C linkage, i.e. does not mangle names that has been compiled with C compiler.

For good explanation how to use C linkage in C++, refer e.g. to this answer here on SO: https://stackoverflow.com/a/1041880/12118546

This is the reason you often see code like this

#ifdef __cplusplus
extern "C" {
#endif

// all of your legacy C code here

#ifdef __cplusplus
}
#endif

Sample from: https://stackoverflow.com/a/12994075/12118546

Cryptic linker errors like these would result if you would forget about this:

...
/home/AbiSfw/ccvvuHoX.o: In function `main':
prog.cpp:(.text+0x19): undefined reference to `foo()'
...

Sample from: https://stackoverflow.com/a/12573818/12118546

Roman Pavelka
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  • You're likely to get quite a few compilation errors when compiling C code as C++, unless the C code was written with this in mind. It's rare to do this in my experience. – interjay Aug 19 '21 at 17:24
  • *compile the C stuff with C++ compiler without any issues* This is bound to end in tears. – NathanOliver Aug 19 '21 at 17:24
  • @interjay Those would be linker error, but I am not going to be a nitpicker here. I will add that to my answer as I was quite a confused when I have seen those for the first time. – Roman Pavelka Aug 19 '21 at 17:27
  • I'm talking about compiler errors, not linker errors. See https://stackoverflow.com/questions/861517/what-issues-can-i-expect-compiling-c-code-with-a-c-compiler – interjay Aug 19 '21 at 17:28
  • Yay, I see now... Allright, adding these notes. – Roman Pavelka Aug 19 '21 at 17:34