EXTERN_C syntax error

Just to elaborate on what what Let_Me_Be has said, the issue is you are not using the macro you have defined correctly.You are missing { and } braces.

Try this...

EXTERN_C {
void eap_radius_init (
                        const char *authsrv,
                        int port,
                        const char *secret,
                        PFN_RADIUS_CALLBACK radius_callback,
                        int hostapd_logger_level);
}

Also you need to modify the macro otherwise this will fail if EXTERN_C is not defined.

Try this...

#define EXTERN_C
#ifndef EXTERN_C
#ifdef __cplusplus
#undef EXTERN_C
#define EXTERN_C extern "C"
#endif
#endif

Just to elaborate even more, extern C won't help you when including C headers into a C++ app.

>> Just to elaborate even more, extern C won't help you when including C headers into a C++ app.
It tells the linker to use C linkage and not C++ linkage, otherwise the linker will be looking for C++ decorated names. So, why do you think this is not going to help? Or, maybe I have misunderstood your point?

Uh, sorry, my bad...

I'm going to do something relaxing, my brain seem to be off.

>> Uh, sorry, my bad...
Heh. No worries... you should see (actually you probably have) some of the gaffs I've made on EE ;)

>> I'm going to do something relaxing, my brain seem to be off.
Enjoy.

the file has name main.c. Is it not enough? What is the function of extern "C" here or __cplusplus?
Occasionally today I had to test something and saw that in my main.c file a function int __cdecl Sum() was decorated just as _Sum. There were no extern "C" at all, for sure.

My point is the following - if php-newbie didn't use these strange things as __cplusplus and extern "C" in c-file, he did make this mistake. So, If I'm right, maybe we can recommend him just remove these stuff from his code?

>> maybe we can recommend him just remove these stuff from his code?
Maybe but I don't think we know enough about what the asker is doing to make the recommendation. But, your premise is reasonable. Go ahead and explore this with php-newbie if you think it is worth while.

Actually I wanted to know your opinion. :)

>> Actually I wanted to know your opinion. :)
Heh. Sneaky. Well, I agree that if there is no valid reason to use specifiers then don't (if nothing else it makes the code ugly) but as I said above, we don't know the context of this code. As it is posted it could just be a micky-mouse example taken from the real code base. It might also be that the leading comment is wrong or mis-leading. But you raise a good point and since it was your point I am happy to stand back and let you ruin with it and, possibly, take all the credit for spotting something Let_Me_Be and I both missed ;)

Ok?

Ok. :)

I do not recommend you to use a macros, if you don't know for sure what it does.
In our case you named the file as main.c. So your code is in C. Microsoft compiler will work accordingly - if you will try to use a C++ stuff, it will complain. You can try, for example, add  include for iostream <IOSTREAM>and use std::cout - the compiler will not allow it.
_cplusplus is defined automatically by compiler when you compile C++ code.

So in our case this code

#ifdef __cplusplus
#define EXTERN_C extern "C"
#endif

is wrong. And it leads to other mistakes. Because later in the code you are trying to use this undefined EXTERN_C:

#ifndef EXTERN_C
#ifdef __cplusplus
#define EXTERN_C extern "C"
#endif
#endif
(it is wrong also logically - EXTERN_C was supposed to be declared when _cplusplus exists, but here you check #ifndef ENTERN_C but #ifdef _cplusplus - it is impossible in your code even if you will use _SOMETHING_ and _SOMETHINGELSE_ instead of cplusplus and EXTERN_C).

More then it, extern "C" is also a mistake - you are in C program anyway. extern "C" is used in C++ program, when you are going to export a function or a variable and your the other side (that imports such functions) is written in C.

Here we may start a long discussion or an article. :)

If you need, we can talk in separate thread about macroses, calling convention, etc.

thanks for all your comments. The code I'm trying to compile (wpa_supplicant) was written in C but they developed a cpp solutions for it. The examples that were provided are still in C so I'm trying to integrate them in the cpp solutions. Let me try out your examples and see if I can get it running. I'll be back.

>> I've got a main.c in which I define EXTERN_C as extern C. I've set the project in VC++ set to compile as C++ project.

pgnatyuk is telling you that one of your problems is that even though you set the project for C++, the .c suffix on the main.c file name causes the compiler to compile your C++ as C.  If you want to compile it as C++, change the file name to main.cpp.

You don't have to use braces with extern "C".  That's just a convenience if you want the extern "C" to apply to multiple declarations.  So I think it should be possible for your macro to work in C++.  If your goal was to be able to compile the same declarations in C, you would need to fix the macro.  The problem with the macro code is that it doesn't do anything when compiled in C, so the compiler still sees the EXTERN_C token, and it doesn't know what it means.  To fix it, you could add macro code that when __cplusplus is not defined, defines EXTERN_C without giving it a value, like this:

#define EXTERN_C

Then the compiler will not see it, so it will not choke on it.

I'll split points with efn since it was an elaboration of his answer.