2

After all I've managed to "prepare" my eclipse for NDK (atleast i think so), it doesnt argue at c code anymore, but now I'm getting "No implementation found for native Lcom" anytime i execute any native code.. It happens on NDK's samples too..

My .java

...    
private native float pi(); 
static
{
    System.loadLibrary("shit");
}
...
System.out.println(pi());
...

My .cpp

#include <jni.h>

jfloat Java_com_example_shit_MainActivity_pi(JNIEnv * env, jobject obj) {
    return 3.1415;
}

My .mk

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := shit
LOCAL_SRC_FILES := shit.cpp

include $(BUILD_SHARED_LIBRARY)

My error log

11-14 18:30:16.231: D/dalvikvm(1739): Trying to load lib /data/data/com.example.shit/lib/libshit.so 0x413b1fc8
11-14 18:30:16.241: D/dalvikvm(1739): Added shared lib /data/data/com.example.shit/lib/libshit.so 0x413b1fc8
11-14 18:30:16.241: D/dalvikvm(1739): No JNI_OnLoad found in /data/data/com.example.shit/lib/libshit.so 0x413b1fc8, skipping init
11-14 18:30:16.271: D/TextLayoutCache(1739): Using debug level: 0 - Debug Enabled: 0
11-14 18:30:17.913: W/dalvikvm(1739): No implementation found for native Lcom/example/shit/MainActivity;.pi ()F
11-14 18:30:17.913: D/AndroidRuntime(1739): Shutting down VM
11-14 18:30:17.913: W/dalvikvm(1739): threadid=1: thread exiting with uncaught exception (group=0x40ab1210)
11-14 18:30:17.923: E/AndroidRuntime(1739): FATAL EXCEPTION: main
11-14 18:30:17.923: E/AndroidRuntime(1739): java.lang.IllegalStateException: Could not execute method of the activity
...
11-14 18:30:17.923: E/AndroidRuntime(1739):     at dalvik.system.NativeStart.main(Native Method)
...
11-14 18:30:17.923: E/AndroidRuntime(1739): Caused by: java.lang.UnsatisfiedLinkError: pi
11-14 18:30:17.923: E/AndroidRuntime(1739):     at com.example.shit.MainActivity.pi(Native Method)
11-14 18:30:17.923: E/AndroidRuntime(1739):     at com.example.shit.MainActivity.doit(MainActivity.java:31)
...

Why do I get that damn "No implementation found for native"???

Rat-a-tat-a-tat Ratatouille
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Nacky
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1 Answers1

12

Since your JNI function is in the C++ source file, it needs to be declared as extern "C" to be compatible with JNI. Otherwise, the C++ name mangling will get in the way of dynamic linking.

Also, your native method does not return a value. It should be a compilation error.

So replace the C function with:

extern "C" {

jfloat Java_com_example_shit_MainActivity_pi(JNIEnv * env, jobject obj) {
    return 3.14;
}

}
Seva Alekseyev
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  • Surround your C++ function with `extern "C"{...}` – Seva Alekseyev Nov 14 '13 at 17:18
  • I cant believe but it HELPS! Thank you SO MUCH! Could you please explain why it helps?? Dumb me, now I understand.. Thank you again ) – Nacky Nov 14 '13 at 17:28
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    The C++ name mangling gets in the way of dynamic linking - the C++ function in the SO file is not called `Java_com_example_shit_MainActivity_pi` anymore. `extern "C"` prevents that. – Seva Alekseyev Nov 14 '13 at 17:43