Question

I am using Eclipse to experiment Android NDK programming. My platform info is as follows:

1. Windows 7.
2. Eclipse platform. I can use this eclipse platform to build android apps without hassle; no problem with it.
3. Cygwin with development package installed. The version of
   “make” is GNU Make 3.81.

I code a very simple native c function as well as Android.mk shown as follows:

———–../jni/get_string_native.c———

#include <jni.h>
#include <string.h>
#include <android/log.h>
#include <stdio.h>

jstring Java_geil_learn_ndk_NDKStringActivity_getString(JNIEnv * env, jobject this, jint value1, jint value2)
{
     char *szFormat = "The sum of the two numbers is: %i";
     char *szResult;

    // add the two values
     jlong sum = value1+value2;

    // malloc room for the resulting string
    szResult = malloc(sizeof(szFormat) + 20);

    // standard sprintf
    sprintf(szResult, szFormat, sum);

    // get an object string
    jstring result = (*env)->NewStringUTF(env, szResult);

    // cleanup
    free(szResult);

   return result;
}

————–../jni/Android.make———-

# LOCAL_PATH := $(call my-dir)  
#   
# include $(CLEAR_VARS)  
#   
# LOCAL_LDLIBS := -llog  
#   
# LOCAL_MODULE    := get_string_native  
# LOCAL_SRC_FILES := get_string_native.c  
#   
# include $(BUILD_SHARED_LIBRARY)

---

Now I tried to use ndk-build to produce the shared library, but nothing happen. Even no error message showed up. See below:

——- From Cygwin terminal ———

Administrator@XP-201011081632 /cygdrive/d/eclipse_projects/workspace/NDKString/jni
$ ndk-build

Administrator@XP-201011081632 /cygdrive/d/eclipse_projects/workspace/NDKString/jni
$

Surely, I have set up the environment variable PATH and build it in \jni.

I am really confused now; please help me!!

---

I have removed # in the Android.make file. Now it can generate the corresponding .so file in /lib. But when I call the native method in an activity, run-time error occurred. Logcat info is as follows. Would u please help me?

Trying to load lib /data/data/geil.learn.ndk.NDKStringAcivity/lib/libnative.so 0x405151f0
Added shared lib /data/data/geil.learn.ndk.NDKStringAcivity/lib/libnative.so 0x405151f0
No JNI_OnLoad found in /data/data/geil.learn.ndk.NDKStringAcivity/lib/libnative.so 0x405151f0, skipping init
60): Displayed geil.learn.ndk.NDKStringAcivity/.NDKStringActivity: +1s145ms
No implementation found for native Lgeil/learn/ndk/NDKStringAcivity/NDKStringActivity;.getString (II)Ljava/lang/String;
344): Shutting down VM threadid=1: thread exiting with uncaught exception (group=0x40015560)
344): FATAL EXCEPTION: main
344): java.lang.UnsatisfiedLinkError: getString
344):        at geil.learn.ndk.NDKStringAcivity.NDKStringActivity.getString(Native Method)
344):        at geil.learn.ndk.NDKStringAcivity.NDKStringActivity.onClick(NDKStringActivity.java:40)
344):        at android.view.View.performClick(View.java:2485)
344):        at android.view.View$PerformClick.run(View.java:9080)
344):        at android.os.Handler.handleCallback(Handler.java:587)
344):        at android.os.Handler.dispatchMessage(Handler.java:92)
344):        at android.os.Looper.loop(Looper.java:123)
344):        at android.app.ActivityThread.main(ActivityThread.java:3683)
344):        at java.lang.reflect.Method.invokeNative(Native Method)
344):        at java.lang.reflect.Method.invoke(Method.java:507)
344):        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
344):        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
344):        at dalvik.system.NativeStart.main(Native Method)
60):   Force finishing activity geil.learn.ndk.NDKStringAcivity/.NDKStringActivity
60): Activity pause timeout for HistoryRecord{407868c8) geil.learn.ndk.NDKStringAcivity/.NDKStringActivity} Sending signal. PID: 344 SIG: 9
60): Process geil.learn.ndk.NDKStringAcivity (pid 344) has died.
60): WIN DEATH: Window{4073a7c0 geil.learn.ndk.NDKStringAcivity/geil.learn.ndk.NDKStringAcivity.NDKStringActivity paused=false}
(60): Got RemoteException sending setActive(false) notification to pid 344 uid 10037
60): Activity destroy timeout for HistoryRecord{407868c8 geil.learn.ndk.NDKStringAcivity/.NDKStringActivity}

Answer 1

As Salw has already pointed out you will need to change the extension.

A # in the .mk file is a comment, you basically your make file is an empty makefile. Remove the # from the .mk file.

Also you will need to give the include directory which contains the header files..