Compiling C code inside a C++ code inside a Objective-C++ code

Question

My problem is a little complex:

Library: I have a library written in C and C++. It compiles perfecly in XCode with Apple LLVM. The work of this library itself is done by the C code while the C++ part is just a C++ interface because I prefer C++. In theory I need to use only C++ to comunicate with it.

The application: I have an application in Objective-C that uses the library above. Of couse, as the communication with my library is done via C++ I need to have a .mm file in order to call my library from "Objective-C++".

During the compilation... several issued of "C" languages happen:

• error: non-const static data member must be initialized out of line
• error: statement expression not allowed at file scope
• etc...

It only happens with Objective-C++

• Objective-C++ (app) -> C++ headers (lib) -> C headers (lib, with extern "C") -> NOT OK!!! WHY?

If I make another C++ application for test of library, it goes ok

• C++ (app) -> C++ (lib) -> C header (lib, with extern "C") -> OK

Detail: I am always using the Apple LLVM compiler here

The question: How do I compile C code from C++ from Objective-C++ code? Why it's different than compile from a regular C++ code?

Answer 1

After a long period of tries and Google I finally could figure out. Before I call my C headers, I should undefine MAX and MIN macros. For some reason they were previous defined. The compiler doesn't show the error with precision. That's why it was difficult. The C framework I am using has it's own declaration of MAX and MIN macros...

Another very interesting thing that might be useful for others is that before we need to do the same thing: undefine max and min (lower case) if we are using some C framework that implements it's own max and min.

It solved both problems.

Answer 2

Don't forget to do

#ifdef __cplusplus
extern "C" {
#endif

<Some C method declaration>

#ifdef __cplusplus
}
#endif

in your header files that contain C method declarations.