How to call a function in CPP file from C File and vice versa in ANDROID NDK?

Question

I am not able to call a function in cpp file from c file and also a function in c file from a cpp file in the ndk itself.

I tried using extern "C" {} as well.

Pasting the code i tried here for reference.

CFileCallingCpp.c:

#include "CFileCallingCpp.h"
//#include "custom_debug.h"
#include "CppFile.h"





void tempFunc() {

}

void printTheLogs() {
    //Its not possible to make use of the CPP class in c file
//  CCustomDebug cls;
//  cls.printErrorLog("This is the error log %d %s", 54321, "aaaaaaaaaaaaaaaaaa");
//  cls.printErrorLog("EXAMPLE", "This is the error log %d %s", 54321, "aaaaaaaaaaaaaaaaaa");
    printTheLogs1();
//  tempFunc();
}

CFileCallingCpp.h:

#ifndef _CFILECALLINGCPP_H_
#define _CFILECALLINGCPP_H_

void printTheLogs();


#endif

CppFile.cpp:

#include "CppFile.h"
#include "custom_debug.h"
#include "CFileCallingCpp.h"

void printTheLogs1() {
    CCustomDebug::printErrorLog("This is the error log %d %s", 54321, "aaaaaaaaaaaaaaaaaa");
    CCustomDebug::printErrorLog("EXAMPLE", "This is the error log %d %s", 54321, "aaaaaaaaaaaaaaaaaa");
}

#if defined(__cplusplus)
extern "C" {
#endif

void callCFileFunc() {
    printTheLogs();
//  printTheLogs1();
}


#if defined(__cplusplus)
}
#endif

CppFile.h:

#ifndef _CPPFILE_H_
#define _CPPFILE_H_

void printTheLogs1();


#endif

Errors i am getting:

    sh-4.1$ /cygdrive/c/Android/android-ndk/ndk-build
    SharedLibrary  : libJNIExInterface.so
    D:/EclipseWorkspace/NativeExample/obj/local/armeabi/objs-debug/JNIExInterface/CppFile.o: In function `callCFileFunc':
    D:/EclipseWorkspace/NativeExample/jni/CppFile.cpp:15: undefined reference to `printTheLogs()'
    D:/EclipseWorkspace/NativeExample/obj/local/armeabi/objs-debug/JNIExInterface/CFileCallingCpp.o: In function `printTheLogs':
    D:/EclipseWorkspace/NativeExample/jni/CFileCallingCpp.c:18: undefined reference to `printTheLogs1'
    collect2: ld returned 1 exit status
    make: *** [/cygdrive/d/EclipseWorkspace/NativeExample/obj/local/armeabi/libJNIExInterface.so] Error 1
    sh-4.1$

Please let me know if anyone knows how to call a cpp code from the c code in ANDROID-NDK.

Regards,
SSuman185

Answer 1

If you call a function from a cpp file that is defined in a c file, you can just use

extern "C" void c_func(); // definition

// from a cpp file
c_func();

You can do the other way around, call a function imlpemented in a cpp file from a c file

// implemnatation in cpp file
extern "C" void cpp_func()
{
    // c++ code allowed here
}

// declaration in .h file
#ifdef _CPLUSPLUS
extern "C" void cpp_func();
#else
extern void cpp_func();
#endif

// from the c file
....
cpp_func();
.....

Answer 2

The extern "C" should be in the header file included by the C source, not in the C++ source file. The same for the C header file included by the C++ source file.