Android studio NDK開發問題記錄之undefined reference to '__android_log_print'

首先進行NDK開發的環境是Android studio3.3.2 + gradle4.10.1 +CMake3.10.2

在新建一個Android studio ndk工程的時候，Android studio會自動給你新建好一個CMakeLists.txt和native-lib.cpp文件。並且CMakeList幫你配置好。

在nativie-lib.cpp文件中使用log是完全沒問題的

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

extern "C" JNIEXPORT jstring JNICALL
Java_com_sven_jnidemo_MainActivity_stringFromJNI(
        JNIEnv* env,
        jobject /* this */) {
    std::string hello = "Hello from C++";
    __android_log_print(ANDROID_LOG_INFO,"msg","patch path:%s","hello world");
    return env->NewStringUTF(hello.c_str());
}

直接Run到手機上可以在log控制檯上看到日誌

但是，如果要重新新建一個完全一樣的cpp文件(當然名稱不一樣)，生成一個新的so庫。就會發現編譯不通過提示“undefined reference to '__android_log_print'

比如在CMakeList.txt進行如下配置

cmake_minimum_required(VERSION 3.4.1)

# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.

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).
        native-lib.cpp)
add_library(
        test-lib

        SHARED

        test.c)
# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries 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 this
# build script, prebuilt third-party libraries, or system libraries.

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

生成一個test-lib的靜態so文件，對應test.c文件,內容和native-lib.cpp內容一樣。編譯的時候會發現test.c這一行

__android_log_print(ANDROID_LOG_INFO,"msg","patch path:%s","hello world");

無法通過，如果在cmake文件中改成

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})
}

會發現native-lib.cpp無法通過，所以猜測target_link_libraries只能一一對應鏈接到log

所以改成

target_link_libraries( # Specifies the target library.
        test-lib

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

編譯通過，兩個so庫都能成功打印出log。

因爲Android studio在後面的版本中都用cmake來構建，所以網上搜索的那些修改gradle文件的方法都不管用。搜了一圈都沒有正確答案。