Question

Please help I search throw whole internet but I can’t find answer …

C Layer

I have created simple function int mean(int, int); and place it in calc_mean.h and initialize it in calc_mean.c here are this two files.

calc_mean.c

#include "calc_mean.h"

int mean(int a, int b)  
{  
return (a+b) / 2;  
}  

calc_mean.h

int mean(int, int);

Then I create make file and build archive (.a) file called Test_Archive.a using following make file

makefile

GCC := C:\Tools\ndk-toolchain\ndk-standalone\bin\arm-linux-androideabi-gcc.exe
GPP := C:\Tools\ndk-toolchain\ndk-standalone\bin\arm-linux-androideabi-g++.exe
AR  := C:\Tools\ndk-toolchain\ndk-standalone\bin\arm-linux-androideabi-ar.exe

default: all

all: obj
    $(AR) r Test_Archive.a *.o

obj:
    $(GPP) -c *.c

I get Test_Archive.a archive file. Now I want to add this archive file to JNI and call mean function from my JNI project, for that I have created JNI and Java files which you can see below.

---

JAVA Layer

How you can see here in java layer I have TestJavaClass that have one native method called JMean this method have two int arguments and return also int.

public class TestJavaClass
{
    /** Default Constructor
     * 
     */
    public TestJavaClass( ) {

    }

    /** Test Function. 
     *  
     * @param a
     * @param b
     * @return
     */
    public native int JMean( int a, int b);
}

---

JNI Layer

This is JNI header file

Test_Library.h

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_Fido_OSTXLib_OSTX */

#ifndef _Included_com_Fido_OSTXLib_OSTX
#define _Included_com_Fido_OSTXLib_OSTX
#ifdef __cplusplus
extern "C" {
#endif

/*
 * Class:     com_Fido_OSTXLib_OSTX
 * Method:    JMean
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_com_Fido_OSTXLib_OSTX_JMean
  (JNIEnv *, jobject, jint, jint);

#ifdef __cplusplus
}
#endif
#endif

Test_Library.c

#include "Test_Library.h"
#include "calc_mean.h"

JNIEXPORT jint JNICALL Java_com_Fido_OSTXLib_OSTX_JMean( JNIEnv* env, jobject thiz, jint a, jint b )
{
    return mean( a, b );
}

I put this two files Test_Library.h, Test_Library.c and calc_mean.h, Test_Archive.a and create make file Android.mk

Android.mk

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE           := Test_Library
LOCAL_SRC_FILES        := Test_Library.c

LOCAL_LDLIBS := -LTest_Archive.a

include $(BUILD_SHARED_LIBRARY)

but when I want to create .so file, the following error occurs, why ?

$ ../../ndk-build Compile thumb : Test_Library <= Test_Library.c
SharedLibrary : libTest_Library.so
C:/cygwin/home/android-ndk-r5b/Fido/ProjectOSTX/obj/local/armeabi/objs/OSTX_Library/OSTX_Library.o:
In function Java_com_Fido_OSTXLib_OSTX_JMean':
C:/cygwin/home/android-ndk-r5b/Fido/ProjectOSTX/jni/OSTX_Library.c:6:
undefined reference tomean’ collect2: ld returned 1 exit status make: *
[/home/android-ndk-r5b/Fido/ProjectOSTX/obj/local/armeabi/libOSTX_Library.so]
Error 1

Why undefined reference to `mean’ ?

Answer 1

As I suppos the main reason was compiler settings, I make some modifications in makefile and my .a archive linked to shared library, here are modifications.

GCC := C:\Tools\ndk-toolchain\ndk-standalone\bin\arm-linux-androideabi-gcc.exe
GPP := C:\Tools\ndk-toolchain\ndk-standalone\bin\arm-linux-androideabi-g++.exe
AR  := C:\Tools\ndk-toolchain\ndk-standalone\bin\arm-linux-androideabi-ar.exe

OPTIONS  :=\
-fpic \
-ffunction-sections \
-funwind-tables  \
-fstack-protector \
-D__ARM_ARCH_5__ \
-D__ARM_ARCH_5T__ \
-D__ARM_ARCH_5E__ \
-D__ARM_ARCH_5TE__ \
-Wno-psabi \
-march=armv5te \
-mtune=xscale \
-msoft-float \
-mthumb \
-Os \
-fomit-frame-pointer \
-fno-strict-aliasing \
-finline-limit=64 \
-DANDROID \
-Wa, \
-O2 \
-DNDEBUG \
-g \

default: all


all: obj
    $(AR) r libtestlibrary.a *.o

obj:
    $(GCC) $(OPTIONS) -c *.c