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cmakefilegnu-maketensorflow-litecc

Why linking .cc file works in make file but linking .c file doesn't?

I'm working on a quite large Makefile from the tensorflow repo and I need to add a file link.

After quite some debugging of a link error, I found out that if my file ends with .cc, then the link error disappears, whereas when linking a .c file, the error appears (file content remains the same).

I am linking the file in a Makefile.inc file:

.
.
.
FL_SRCS := \
tensorflow/lite/vis_mi/main.cc \
myFunctions.c \ -->>>>IF I CHANGE THE FILENAME TO myFunctions.cc and link to this .cc file here, it works!!
.
.
.
# Builds a standalone binary.
$(eval $(call vis_test,vis_mi,\
$(FL_SRCS),$(FL_HDRS)))

The link error when using the .c ending ends with:

tensorflow/lite/vis_mi/main.o: In function `main':
tensorflow/lite/vis_mi/main.cc:183: undefined reference to `printMsg()'
../downloads/gcc_embedded/bin/../lib/gcc/arm-none-eabi/7.3.1/../../../../arm-none-eabi/bin/ld: link errors found, deleting executable `tensorflow/lite/vis_mi'
collect2: error: ld returned 1 exit status
gmake: *** [tensorflow/lite/vis_mi/Makefile.inc:578: tensorflow/lite/vis_mi/bin/micro_speech] Error 1

The .c file code:

#include <stdio.h>
#include "myFunctions.h"


void printMsg(){
    //do something here
}

And the header file:

#ifndef MYFUNCTIONS_H
#define MYFUNCTIONS_H

void printMsg();
#endif /* MYFUNCTIONS_H */

How can I include a file ending with .c? Makefiles are fairly new to me, and didn't want to include all the details, and if you need any further details from the Makefile to answer this question I'm happy to edit my post.

Solution

  • The name resolution for C and C++ functions is different. This is sometimes causing problem to "C" code that is also valid "C++". For example:

    int foo(int x) { return x+1 } ;

    The code Will create a function called 'foo' when compiled as "C", and will create a function called '_Z3fooi' when compiled as C++. Decoding the C++ name will (using c++filt) will show foo(int). The reason for the difference is that C++ support polymorphic functions (and methods), so that function names also identify the type of their parameters.

    The proper solution is to decide on the language of the code. C++ and C are different language, and while it's possible to write code that will be valid for both, it will limit the ability to leverage each function abilities.

    Important constraint: If a project contain both C and C++ code, it is important to remember that only functions that follow the "C" conventions can be called between the languages. This is usually implemented with extern "C" directive, and with #ifdef __cplusplus:

    See more: https://www.thegeekstuff.com/2013/01/mix-c-and-cpp/ How to call C++ function from C? Call a C function from C++ code