NBEclipse does not compile .c files

[Anguel]

Hi,

I would like to share some code in a .c file between Netburner and STM32.
Unfortunately, NBEclipse does not seem to compile those .c files, if I rename them to .cpp they compile fine.
Is there a way to fix this?

Thanks,
Anguel

[TomNB]

Hello Anguel,

This is a C vs C++ issue, not an eclipse issue. Any time you want to use functions in a .cpp file that are located in a .c file, you must reference it as extern "C". It is called name mangling: https://www.tutorialspoint.com/name-man ... -cplusplus. Does the compiler you are using for the STM32 support C++? If so, making them both .cpp would be easiest.

[Anguel]

Hi Tom,

Thanks for the help. I actually tried to add the extern "C" but maybe I did something wrong as it did not work.
Now I renamed to .cpp and the STM32 compiles fine.

Thanks,
Anguel

[TomNB]

Hi,

Just in case it comes up in the future, here is an example. Normally you would use header files, but just trying to make this simple.

Lets say you have a file foo.c with a function funcFoo():

Code: Select all

void funcFoo()
{
	iprintf("Executing funcFoo\r\n");
}

In your main.cpp you then try to call it:

Code: Select all

extern void funcFoo();

void UserMain(void * pd) {
    InitializeStack();
    GetDHCPAddressIfNecessary();
    OSChangePrio(MAIN_PRIO);
    EnableAutoUpdate();
    StartHTTP();
    
    iprintf("Application started\n");

    funcFoo();

    while (1) {
        OSTimeDly(TICKS_PER_SECOND);
    }
}

But the error you get is:
C:\nburn\workspace\AppWiz\Release/..\main.cpp:36: undefined reference to `funcFoo()'

This is because with C++ name mangling the signature of funcFoo doesn't match what is in foo.c. So lets change the extern in main.cpp to:

Code: Select all

extern "C" {
	void funcFoo();
}

Now it builds fine. The bracket format is used so you can add as many C functions as you want between the brackets, but if its just one you could make it extern "C" funcFoo();

[Anguel]

UPDATE:
It turned out just changing the file to .cpp did NOT work as the STM32CubeIDE (Eclipse based) project is set to C, not to C++ right now, so it just did not compile the .cpp at all but used a version of the old .c I had previously compiled.
That confused me as it built ok until I changed the file.

The problem that my previous extern "C" experiments did not work was actually that I had not included the #ifdef __cplusplus part and this confused the C-only compiler of the STM32:
#ifdef __cplusplus
extern "C" {
#endif

See here: https://isocpp.org/wiki/faq/mixing-c-an ... s-personal

So this is very important to make the C-only compiler skip the extern "C" it does not understand. This is at least how I understand things so far.
It finally seeams to work fine now: with a .c file and the #ifdef __cplusplus part.

Anguel

[Anguel]

Now my problems continue. I wanted to use the Get_msec() function into my .c file shared between Netburner and STM32. It is conditionally compiled on the Netburner platform only, together with a conditionally added #include <utils.h>

The problem is that when I add these, suddenly hundreds of errors appear:

Errors_when_including_utils.h_for_Netburner.png (31.47 KiB) Viewed 18339 times

I think this may have something to do with the
#ifdef __cplusplus
extern "C" {
#endif
added in the corresponding .h file.
Any idea how to solve this?

[TomNB]

Hello,

I don't think there is anything NetBurner specific here, but in general its mixing C and C++ code with the NNDK using gcc. Eclipse does not compile anything, it is just an editor and project manager. I am not familiar with the STM32CubeIDE, or what compiler it uses to build those projects. So any information you can find on mixing C and C++ should be applicable. Doing a quick search I found this:
https://www.oracle.com/technical-resour ... splus.html

I have not tried to call a C++ function from a C source file, but it sounds like there are a lot of issues to consider. Also this:

https://www.quora.com/How-do-I-call-a-C ... ion-from-C
"About calling C++ functions and class member functions ‘as is’ from C, there is no easy and obvious way to do it. What you can do is, expose a C API of your codes written in C++ and use that API in C. You can go through the book mentioned above and explore ideas about creating elaborate C APIs for object oriented code written in C++."

I hope these references are of some help.

[Anguel]

When I add the "extern "C"" but then have to #include a header from Nbrtos something does not work out well and all the errors are thrown. Maybe it is a configuration error, maybe it is because these headers expect C++, not C.

Actually I am not mixing C and C++, I just want a .c file to be compiled as if it were a .cpp by the the NB Eclipse. The problem is that NB invokes GCC instead of G++ when it sees a .c file. I don't want that to happen, I want the C++ compiler to process it as if it were a .cpp file.

Meanwhile I found out that there is a "-x c++" switch that can be passed to the compiler to do what I want.
But I am not sure if it is still supported by the latest gcc version and where exactly I should add it into the Eclipse NB config.
I am sure your expert who configures the toolchain has an idea how to do it properly. Thanks in advance.

Anguel

[TomNB]

I will check on that. But in your previous post you made the statement below. Wouldn't that be the same when forcing G++?

Post by Anguel » Thu Nov 05, 2020 9:22 am
UPDATE:
It turned out just changing the file to .cpp did NOT work as the STM32CubeIDE (Eclipse based) project is set to C, not to C++ right now, so it just did not compile the .cpp at all but used a version of the old .c I had previously compiled.
That confused me as it built ok until I changed the file.

[Anguel]

Finally I managed to compile successfully with a workaround. STM32CubeIDE is configured C only and just ignores all .cpp files. So I did a simple
#include "file.cpp"
in a file.c and now STM32 compiles the code as C while Netburner compiles it as C++, of course file.c has to be in a folder NB does not know about, otherwise it also tries to compile it in addition.
Such a nightmare and so many hours spent to just share a single file with code between a C and a C++ project. I would be still happy if someone can tell me what caused all those errors when I work with "extern "C"" and want to use a Nbrtos function at the same time.