Android ndk (cmake): 'undefined reference to `__android_log_write' when using log api in the second jni library

Question

I am using Android Studio 2.2 and cmake to create a jni file.

I want to show the log of the jni file, but get the error message "undefined link to` __android_log_write".

My CMakeLists.txt file:

add_library( # Sets the name of the library. native-lib # Sets the library as a shared library. SHARED # Provides a relative path to your source file(s). # Associated headers in the same location as their source # file are automatically included. src/main/cpp/native-lib.cpp ) add_library( # Sets the name of the library. test-lib # Sets the library as a shared library. SHARED # Provides a relative path to your source file(s). # Associated headers in the same location as their source # file are automatically included. src/main/cpp/test-lib.cpp ) include_directories( src/main/jni/ ) # Searches for a specified prebuilt library and stores the path as a # variable. Because system libraries are included in the search path by # default, you only need to specify the name of the public NDK library # you want to add. CMake verifies that the library exists before # completing its build. find_library( # Sets the name of the path variable. log-lib # Specifies the name of the NDK library that # you want CMake to locate. log ) # Specifies libraries CMake should link to your target library. You # can link multiple libraries, such as libraries you define in the # build script, prebuilt third-party libraries, or system libraries. target_link_libraries( # Specifies the target library. test-lib native-lib # Links the target library to the log library # included in the NDK. ${log-lib} ) 

And my two jni files are the same as below, without function name

 JNIEXPORT jstring JNICALL Java_com_cyweemotion_www_jnitest_MainActivity_stringFromJNI (JNIEnv *env, jobject){ __android_log_write(ANDROID_LOG_ERROR, "Tag", "Error here"); std::string hello = "Hello from C++"; return env->NewStringUTF(hello.c_str()); }; 

My build.gradle (Module: app)

  android { compileSdkVersion 23 buildToolsVersion "24.0.3" defaultConfig { minSdkVersion 19 targetSdkVersion 24 versionCode 2 versionName '1.02' testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner" externalNativeBuild { cmake { cppFlags "" } } } buildTypes { release { minifyEnabled false proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro' signingConfig signingConfigs.config } debug { jniDebuggable false } } externalNativeBuild { cmake { path "CMakeLists.txt" } } productFlavors { } } 

According to android document: add C and C ++ code to your project . I think I can use log api.

What is wrong with my code or my setup?

---

Update:

I found that this is not a problem in my first jni library (update code).

This is only a mistake in the second library.

ex: target_link_libraries (test-lib, native-lib , ...), native-lib is the second loadable library.

So native-lib cannot use log api.

Now I can only remove native-lib. However, I really want to know why?

Answer 1

I finally found that I had to separate this link.

 target_link_libraries( # Specifies the target library. test-lib native-lib # Links the target library to the log library # included in the NDK. ${log-lib} ) target_link_libraries( # Specifies the target library. native-lib # Links the target library to the log library # included in the NDK. ${log-lib} )