一、前言

目前Android编译.so的话使用Android Studio比较简单，但是有时候时候Android Studio的话还需要创建一个Android的项目，这里记录下脱离Android Studio单纯使用Cmake和C++开发工具Clion(或者其他的开发工具也行,这些开发工具和Android Studio不一样，哪一种工具都行)。
实际上编译.so还有比较简单的方式。比如直接在linux环境下面使用cmake编译c++项目即可，这时候出现的就是.so库。但是如果开发环境是Mac或者Windows的话，就会生成dylib或者exe文件，不是我们想要的文件，所以就需要使用交叉编译的技术。
Cmake对于编译Android的.so文件提供了两种方式: NDK或者交叉工具链。由于本人从事Android开发，有现成的NDK依赖，而交叉编译链需要下载。所以就使用NDK进行编译，不过根据此进行修改，大概也是可以的。后续有空会记录使用交叉工具链的编译方式。
项目比较乱，后面再做整理

二、相关代码

开发工具为CLion，需要注意的是Android Studio和CLion都采用了ninja构建系统，如果使用其他构建系统需要进行修改，不过文中代码已经有该代码，到时候改下路径即可
整体项目结构如下:

这其中的核心代码为:
需要注意的是该代码需要写在project(untitled VERSION 1.0)函数调用之前

# control where the static and shared libraries are built so that on windows
# we don't need to tinker with the path to run the executable
set(CMAKE_SYSTEM_NAME Android)
set(CMAKE_SYSTEM_VERSION 21) # API level
set(CMAKE_ANDROID_ARCH_ABI arm64-v8a)
set(CMAKE_ANDROID_NDK /Users/c/Documents/sdk/android/ndk/25.1.8937393)
set(CMAKE_MAKE_PROGRAM /Users/c/Documents/sdk/android/cmake/3.22.1/bin/ninja)
#set(CMAKE_ANDROID_STL_TYPE gnustl_static) # 需要注意的是NDK不支持这个属性，可能是NDK版本原因，所以使用c++_shared，
set(CMAKE_ANDROID_STL_TYPE c++_shared)
set(CMAKE_EXPORT_COMPILE_COMMANDS NO)

CMakeLists.txt

cmake_minimum_required(VERSION 3.23) # 这是Cmake版本

#======这一段来自Android开发者平台:https://developer.android.google.cn/ndk/guides/cmake?hl=zh-cn#using_prebuilt_libraries 
#-DCMAKE_FIND_ROOT_PATH=${HOME}/Dev/github-projects/googlesamples/ndk-samples/hello-jni/app/.cxx/cmake/universalDebug/prefab/armeabi-v7a/prefab
#-DCMAKE_BUILD_TYPE=Debug
#-DCMAKE_TOOLCHAIN_FILE=${HOME}/Android/Sdk/ndk/22.1.7171670/build/cmake/android.toolchain.cmake
#-DANDROID_ABI=armeabi-v7a
#-DANDROID_NDK=${HOME}/Android/Sdk/ndk/22.1.7171670
#-DANDROID_PLATFORM=android-23
#-DCMAKE_ANDROID_ARCH_ABI=armeabi-v7a
#-DCMAKE_ANDROID_NDK=${HOME}/Android/Sdk/ndk/22.1.7171670
#-DCMAKE_EXPORT_COMPILE_COMMANDS=ON
#-DCMAKE_LIBRARY_OUTPUT_DIRECTORY=${HOME}/Dev/github-projects/googlesamples/ndk-samples/hello-jni/app/build/intermediates/cmake/universalDebug/obj/armeabi-v7a
#-DCMAKE_RUNTIME_OUTPUT_DIRECTORY=${HOME}/Dev/github-projects/googlesamples/ndk-samples/hello-jni/app/build/intermediates/cmake/universalDebug/obj/armeabi-v7a
#-DCMAKE_MAKE_PROGRAM=${HOME}/Android/Sdk/cmake/3.10.2.4988404/bin/ninja
#-DCMAKE_SYSTEM_NAME=Android
#-DCMAKE_SYSTEM_VERSION=23

#====== end ======


# control where the static and shared libraries are built so that on windows
# we don't need to tinker with the path to run the executable
set(CMAKE_SYSTEM_NAME Android)
set(CMAKE_SYSTEM_VERSION 21) # API level
set(CMAKE_ANDROID_ARCH_ABI arm64-v8a)
set(CMAKE_ANDROID_NDK /Users/c/Documents/sdk/android/ndk/25.1.8937393)
set(CMAKE_MAKE_PROGRAM /Users/c/Documents/sdk/android/cmake/3.22.1/bin/ninja)
#set(CMAKE_ANDROID_STL_TYPE gnustl_static) # 需要注意的是NDK不支持这个属性，可能是NDK版本原因，所以使用c++_shared，
set(CMAKE_ANDROID_STL_TYPE c++_shared)
set(CMAKE_EXPORT_COMPILE_COMMANDS NO)

set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY "${PROJECT_BINARY_DIR}")
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY "${PROJECT_BINARY_DIR}")
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY "${PROJECT_BINARY_DIR}")

project(untitled VERSION 1.0)

add_subdirectory(libscanner)
configure_file(square.h.in square.h)

# specify the C++ standard
add_library(tutorial_compiler_flags INTERFACE)
target_compile_features(tutorial_compiler_flags INTERFACE cxx_std_11)


# 通过BUILD_SHARED_LIBS 创建共享库，后面值需要设置为ON
option(BUILD_SHARED_LIBS "Build using shared libraries" ON)

add_executable(untitled square_main.cpp)

target_link_libraries(untitled PUBLIC scanner tutorial_compiler_flags)
target_include_directories(untitled PUBLIC
        "${PROJECT_BINARY_DIR}"
        "${PROJECT_SOURCE_DIR}/libscanner"
        )

# 打印日志
message("---PROJECT_BINARY_DIR--${PROJECT_BINARY_DIR}")
message("---PROJECT_SOURCE_DIR--${PROJECT_SOURCE_DIR}")
message("---libscanner头文件--${PROJECT_SOURCE_DIR}/libscanner")

libscanner/CMakeLists.txt

#-DCMAKE_FIND_ROOT_PATH=${HOME}/Dev/github-projects/googlesamples/ndk-samples/hello-jni/app/.cxx/cmake/universalDebug/prefab/armeabi-v7a/prefab
#-DCMAKE_BUILD_TYPE=Debug
#-DCMAKE_TOOLCHAIN_FILE=${HOME}/Android/Sdk/ndk/22.1.7171670/build/cmake/android.toolchain.cmake
#-DANDROID_ABI=armeabi-v7a
#-DANDROID_NDK=${HOME}/Android/Sdk/ndk/22.1.7171670
#-DANDROID_PLATFORM=android-23
#-DCMAKE_ANDROID_ARCH_ABI=armeabi-v7a
#-DCMAKE_ANDROID_NDK=${HOME}/Android/Sdk/ndk/22.1.7171670
#-DCMAKE_EXPORT_COMPILE_COMMANDS=ON
#-DCMAKE_LIBRARY_OUTPUT_DIRECTORY=${HOME}/Dev/github-projects/googlesamples/ndk-samples/hello-jni/app/build/intermediates/cmake/universalDebug/obj/armeabi-v7a
#-DCMAKE_RUNTIME_OUTPUT_DIRECTORY=${HOME}/Dev/github-projects/googlesamples/ndk-samples/hello-jni/app/build/intermediates/cmake/universalDebug/obj/armeabi-v7a
#-DCMAKE_MAKE_PROGRAM=${HOME}/Android/Sdk/cmake/3.10.2.4988404/bin/ninja
#-DCMAKE_SYSTEM_NAME=Android
#-DCMAKE_SYSTEM_VERSION=23

#set(CMAKE_SYSTEM_NAME Android)
#set(CMAKE_SYSTEM_VERSION 21) # API level
#set(CMAKE_ANDROID_ARCH_ABI arm64-v8a)
#set(CMAKE_ANDROID_NDK /Users/c/Documents/sdk/android/ndk/25.1.8937393)
#set(CMAKE_ANDROID_STL_TYPE gnustl_static)
#set(CMAKE_EXPORT_COMPILE_COMMANDS NO)

add_library(scanner scanner.cpp) # 默认编译成静态库
# state that anybody linking to us needs to include the current source dir
# to find MathFunctions.h, while we don't.
target_include_directories(scanner
        INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}
        )

#add_executable(MakeTable scanner.cpp)
#target_link_libraries(MakeTable PRIVATE tutorial_compiler_flags)
aux_source_directory(. SRC_LIST) #把当前目录(.)下所有源代码文件和头文件加入变量SRC_LIST
#ADD_EXECUTABLE(hello ${SRC_LIST}) #生成应用程序 hello (在windows下会自动生成hello.exe)


# 将相关文件添加到SqrtLibrary库
add_library(SqrtLibrary SHARED
       ${SRC_LIST}
        )


# 文件应该去哪个路径下面查找
target_include_directories(SqrtLibrary PRIVATE
        ${CMAKE_CURRENT_BINARY_DIR}
        )

# 将tutorial_compiler_flags库链接到SqrtLibrary
target_link_libraries(SqrtLibrary PUBLIC tutorial_compiler_flags)

# 将SqrtLibrary库链接到libscanner
target_link_libraries(scanner PRIVATE SqrtLibrary)

# 将tutorial_compiler_flags库链接到libscanner
target_link_libraries(scanner PUBLIC tutorial_compiler_flags)


message("YM--->${BUILD_SHARED_LIBS}")

# state that SqrtLibrary need PIC when the default is shared libraries
set_target_properties(SqrtLibrary PROPERTIES
        POSITION_INDEPENDENT_CODE ${BUILD_SHARED_LIBS}
        )

三、参考链接

1. Android 官网的CMake介绍
2. 深入理解使用CMake编译 NDK 程序
3. cmake-toolchains(7)
4. android/ndk-samples
5. CMAKE 在Linux下 构建android 编译、打包、发布环境
6. android 交叉编译常用库（cmake