CODEWITHSUNDEEP
androidc++android-ndk
GingerJim
GingerJim

Reputation: 3907

Android NDK c++ helloworld program crash

As a Android NDK starter, I try to run helloJni example that I found in ndk website here: https://developer.android.com/ndk/samples/sample_hellojni.html

I managed to compile and run with program with the c code provided in the project. However, I want to convert the code into C++ equivalent. Hours have been spent with no success.

What I have done:

rename jni/hello-jni.c -> jni/hello-jni.cpp

change in jni/android.mk

LOCAL_SRC_FILES := hello-jni.c

to 

LOCAL_SRC_FILES := hello-jni.cpp

replacing c code with following c++ code in jni/hello-jni.cpp

#include <string.h>
#include <jni.h>

JNIEXPORT jstring JNICALL
  Java_com_example_hellojni_HelloJni_stringFromJNI
  (JNIEnv *env, jobject obj)
  {
        return env->NewStringUTF("Hello from C++ over JNI!");
  }

Building is successful with output

/home/wenchao/Projects/shared/android-ndk-r10e/ndk-build all 
Android NDK: WARNING: APP_PLATFORM android-21 is larger than android:minSdkVersion 8 in ./AndroidManifest.xml    
[arm64-v8a] Install        : libhello-jni.so => libs/arm64-    v8a/libhello-jni.so
[x86_64] Install        : libhello-jni.so => libs/x86_64/libhello-jni.so
[mips64] Install        : libhello-jni.so => libs/mips64/libhello-jni.so
[armeabi-v7a] Install        : libhello-jni.so => libs/armeabi-v7a/libhello-jni.so
[armeabi] Install        : libhello-jni.so => libs/armeabi/libhello-jni.so
[x86] Install        : libhello-jni.so => libs/x86/libhello-jni.so
[mips] Install        : libhello-jni.so => libs/mips/libhello-jni.so

18:09:12 Build Finished (took 412ms)

But on my device , I got 

Unfortunately, HelloJni is stopped.

And very strange, No output in Logcat. Logcat is completely blank. (this might be a separate issue I need to fix , though)

I do not know how to debug at all :(

Upvotes: 2

Views: 548

Answers (1)

GingerJim
GingerJim

Reputation: 3907

Got it.

We need the extern "C" wrap arround the c++ code

#include <string.h>
#include <jni.h>
extern "C" {


JNIEXPORT jstring JNICALL
  Java_com_example_hellojni_HelloJni_stringFromJNI
  (JNIEnv *env, jobject obj)
  {
    return env->NewStringUTF("Hello from C++ over JNI!");
  }
}

Upvotes: 3

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