LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
# 要生成的.so库名称。java代码System.loadLibrary("hello");加载的就是它
LOCAL_MODULE := hello
# C++文件
LOCAL_SRC_FILES := hello.cpp
include $(BUILD_SHARED_LIBRARY)

# 不写 APP_ABI 会生成全部支持的平台,目前支持：armeabi arm64-v8a armeabi-v7a
# APP_ABI := armeabi arm64-v8a armeabi-v7a mips mips64 x86 x86_64
APP_ABI := armeabi arm64-v8a armeabi-v7a

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html
# Sets the minimum version of CMake required to build the native library. 
# 指定CMake的最小版本
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.
# 设置模块名为 native-lib，SHARED 可分享的，以及配置源文件的路径
add_library( # Sets the name of the library. 设置模块名
             native-lib
             # Sets the library as a shared library. 
             SHARED 
             # Provides a relative path to your source file(s). 文件路径
             src/main/cpp/native-lib.cpp )
# 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.
# 找到 log 本地模块
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.
# 关联 native-lib 模块和 log 模块
target_link_libraries( # Specifies the target library.
                       native-lib
                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )

#include <jni.h>
#include <string>
extern "C"
JNIEXPORT jstring JNICALL
Java_com_haohao_ndk_1cpp_MyJNI_stringFromJNI(JNIEnv *env, jobject instance) {
    std::string hello = "Hello from C++";
    return env->NewStringUTF(hello.c_str());
}

# 指定CMake的最小版本
cmake_minimum_required(VERSION 3.4.1)
add_library( # Sets the name of the library. 设置模块名
             native-lib
             # Sets the library as a shared library. 
             SHARED 
             # Provides a relative path to your source file(s). 文件路径
             src/main/cpp/native-lib.cpp )