Why is NDK throwing Undefined Reference error on Build?

Question

I've got this error while I'm trying to build an library with ndk:

$ /cygdrive/d/android-ndk-r10d/ndk-build.cmd [armeabi] SharedLibrary : libgame.so

jni/core/src/coreApplication.cpp:9: error: undefined reference to 'CCoreMessaging::CCoreMessaging()'

jni/core/src/coreApplication.cpp:11: error: undefined reference to 'CCoreScreenContainer::CCoreScreenContainer()'

jni/core/src/coreReference.h:75: error: undefined reference to 'CCoreRefClass::_RemoveRef(void*, bool)'

jni/core/src/coreReference.h:76: error: undefined reference to 'CCoreRefClass::_AddRef(void*, bool)'

jni/core/src/coreReference.h:58: error: undefined reference to 'CCoreRefClass::_RemoveRef(void*, bool)'

jni/core/src/coreReference.h:58: error: undefined reference to 'CCoreRefClass::_RemoveRef(void*, bool)'

jni/core/src/coreApplication.h:12: error: undefined reference to 'CCoreMessaging::~CCoreMessaging()'

jni/core/src/coreReference.h:58: error: undefined reference to CCoreRefClass::_RemoveRef(void*, bool)'

collect2.exe: error: ld returned 1 exit status

make.exe: *** [obj/local/armeabi/libgame.so] Error 1

coreApplication.h:

<other includes>
#include "coreResources.h"
#include "coreMessaging.h"

class CCoreApplication
{
public:
CCoreApplication(CCoreContext& a_context);
virtual ~CCoreApplication() {} 

CCoreScreenContainer& GetScreenContainer() { return *m_screenContainer; }
CCoreMessaging& GetMessages() { return m_messages; }

<other functions and properties>
CCoreMessaging m_messages;
};

coreApplication.cpp

#include "coreApplication.h"
#include "coreMessaging.h"
#include "coreScreenContainer.h"
<other includes>

CCoreApplication::CCoreApplication(CCoreContext& a_context):
 m_context(a_context)
{
m_screenContainer = new CCoreScreenContainer;
GetScreenContainer().SetBounds(CRectangle(0,0, a_context.GetPlatformHandler()->GetResolutionWidth(), a_context.GetPlatformHandler()->GetResolutionHeight()));
}

coreMessaging.h:

class CCoreMessaging
{
public:
CCoreMessaging(); 
~CCoreMessaging();
void SendMessage(int a_messageID, void* argument0=0, void* argument1=0);
void AddMessageHandler(CCoreMessageHandle& handle, CCoreMessageDelegate handler);
void RemoveMessageHandler(CCoreMessageHandle& handle);
protected:
typedef std::map<int, CCoreMessageDelegate> Map;
Map m_Delegates;
int m_AutoIncrement;
int m_SelfID;
static int m_SelfIDIncrement;
};

coreMessaging.cpp

#include "coreMessaging.h"
<other functions>

CCoreMessaging::CCoreMessaging() : m_AutoIncrement(1)
{
m_SelfID = m_SelfIDIncrement++;
gMessaging[m_SelfID] = this;
if(m_SelfID > 127)
    throw std::runtime_error("too many messaging instances");
}

coreReference.h

class MFAPI CCoreRefClass
{
public:
virtual void Delete() { delete this; }

void _AddRef(void* cls, bool strong);
void _RemoveRef(void* cls, bool strong);

void _IncRef();
bool _DecRef(); // returns true if reference decrease has lead to destruction. false if object is still valid
protected:
CCoreRefClass();
virtual ~CCoreRefClass();

typedef CCoreRefPtr<CCoreRefClass,false> RefType;
std::vector<RefType*> m_refData;

int m_refCount;
};

coreReference.cpp

#include "coreReference.h"

<other functions>
void CCoreRefClass::_RemoveRef( void* cls, bool strong )
{
RefType* refCls = (RefType*)cls;
int lastIdx=(int)m_refData.size()-1;
int refIdx = refCls->m_arrayIndex;
refCls->m_arrayIndex = -1;

// swap erase reference
m_refData[refIdx] = m_refData[lastIdx];
m_refData[refIdx]->m_arrayIndex = refIdx;
m_refData.pop_back();

if(strong)
    _DecRef();
}

void CCoreRefClass::_AddRef( void* cls, bool strong )
{
if(strong)
    _IncRef();

RefType* refCls = (RefType*)cls;
m_refData.push_back(refCls);
refCls->m_arrayIndex = (int)m_refData.size()-1;
}

Most of these errors seem to be produced by a typo, but this code does compile in visual studio as lib completely. I hope it's just something I missed or haven't seen. Feel free to ask for more if needed.

EDIT: application.mk

APP_STL := gnustl_static
APP_CPPFLAGS += -std=c++11
NDK_TOOLCHAIN_VERSION := 4.8
APP_PLATFORM := android-14

android.mk

LOCAL_PATH:=$(call my-dir)
include $(CLEAR_VARS)     
# Here we give our module name and source file(s)

LOCAL_MODULE    := game
LOCAL_SRC_FILES := coreBridge.cpp core/game.cpp core/src/coreApplication.cpp
LOCAL_LDLIBS :=  -llog -lGLESv2

include $(BUILD_SHARED_LIBRARY)
#include $(BUILD_EXECUTABLE)

Answer 1

thanks to Bogdan V. I found out I needed to include all the source files. But instead of linking them all separately, they're all linkable at once:

Android.mk:

LOCAL_PATH:=$(call my-dir)
include $(CLEAR_VARS)

# Here we give our module name and source file(s)

LOCAL_MODULE    := libgame
LOCAL_SRC_FILES := coreBridge.cpp core/game.cpp

FILE_LIST := $(wildcard $(LOCAL_PATH)/../../../core/src/*.cpp)
LOCAL_SRC_FILES += $(FILE_LIST:$(LOCAL_PATH)/%=%) LOCAL_C_INCLUDES += $(LOCAL_PATH)/../../../core/include

LOCAL_LDLIBS :=  -llog -lGLESv2
LOCAL_CPP_FEATURES += exceptions
LOCAL_SHARED_LIBRARIES := libgame.so

include $(BUILD_SHARED_LIBRARY)
#include $(BUILD_EXECUTABLE)

where :

FILE_LIST := $(wildcard $(LOCAL_PATH)/../../../core/src/*.cpp)
LOCAL_SRC_FILES += $(FILE_LIST:$(LOCAL_PATH)/%=%) LOCAL_C_INCLUDES += $(LOCAL_PATH)/../../../core/include

Is the important part to link them all. This allowed me to create the .so after all.

Answer 2

You didn't add to the build the files that define those symbols:

coreMessaging.cpp
coreReference.cpp

presumably

coreScreen.cpp (that i don't see here).

Including the headers means only adding the declarations. You need to compile the sources to get object files that contain the actual symbols that are user at link time.