AndroidStudio CMakeList配置

用户可以新建个工程，对C++ include 打勾就是C++支持的工程了，我们这里要对build.gradle里的相关配置做了解

1、build.gradle中的配置

externalNativeBuild {
            cmake {
                cppFlags ""
                path "CMakeLists.txt"
            }
        }

这个离cppFlags 是针对C++的在android开发中的配置例如：
cppFlags “-std=c++14 -frtti -fexceptions”
-std=c++14：这个是C++的版本配置，为14
-frtti：这个是是NDK对C++ RTTI的支持，在NDK R5的时候就支持了Rtti，只不过为了通用性的原因，默认是不支持的，需要用户手动开启
那么什么是RTTI呢，RTTI 全英文，Runtime Type Information，是运行时能够识别类或者变量的类型特写，类似java中的反射，
-fexceptions：这个是支持C++的异常控制，这个是也NDKR5 就支持的特写，为了通用性原因，默认不支持，需要手动打开
path “CMakeLists.txt”：这个就是CMakeLists的路径配置了，现在这个就是根目录下的文件

2、CMakeList文件的介绍

# 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.

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).
             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.

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

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

上面这个是我拷贝的默认配置

cmake_minimum_required(VERSION 3.4.1)

这个是CMake的配置版本

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).
             src/main/cpp/native-lib.cpp )

这个是添加自己导入或者编写的C++源文件的作用
native-lib：这个是编译成so库的名称，生成的so会在前面加lib，比如这个最后生成的so：libnative-lib.so
这个要和java源文件对应的要一致

static {
        System.loadLibrary("native-lib");
    }

SHARED：这个代表是共享库，.so是共享库，如果不加SHARED默认是静态库，生成.a
src/main/cpp/native-lib.cpp:这个代表参加编译的C++源文件的路径，如果是多个源文件就依次添加多个就可以了

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 )

这个是搜索NDK默认支持的库，这里面就搜索android中LOG日志库，并且设置变量为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} )

这个是要链接的库的目录，
native-lib：这个就是之前我们自己的写的库的变量
${log-lib} ：这个是前面系统的log的变量
CMakeList中的配置还有很多，暂时就说这么多了，