CMAKE_TOOLCHAIN_FILE

absolute or relative path to a cmake script which sets up all the toolchain related variables mentioned above

CMAKE给交叉编译预留了一个变量CMAKE_TOOLCHAIN_FILE，它定义了一个.cmake文件的路径，该文件里面设置了一系列CMAKE变量和属性，比如C_COMPILER，CXX_COMPILER等。.cmake文件的好处是一次编写多次使用，不同平台架构的交叉编译工具链可以编写一个独立的toolchain.cmake文件，而工程的CMakeLists.txt可以编写为通用格式，对工具链不可见。cmake脚本可以如下形式：

cmake -DCMAKE_TOOLCHAIN_FILE=./toolchains/ndk64-toolchain.cmake .. && make

cmake -DCMAKE_TOOLCHAIN_FILE=./toolchain/ndk32-toolchain.cmake .. && make

toolchain.cmake demo

set(CMAKE_SYSTEM_NAME Android)

set(CMAKE_ANDROID_API 21)
set(CMAKE_ANDROID_ARCH_ABI aarch64)
set(CMAKE_ANDROID_STL_TYPE gnustl_static)

set(TOOLCHAIN_PATH /opt/sdk/android-aarch64)
# set(ANDROID_LIB_PATH ${TOOLCHAIN_PATH}/sysroot/usr/lib)

set(CMAKE_C_COMPILER ${TOOLCHAIN_PATH}/bin/aarch64-linux-android-gcc)
set(CMAKE_C_FLAGS "-D__ANDROID_API__=21  -fno-exceptions -O2 -fpie -fpic -fPIE -fPIC -pie -lm -Wl,-llog" CACHE STRING "" FORCE)

set(CMAKE_CXX_COMPILER ${TOOLCHAIN_PATH}/bin/aarch64-linux-android-g++)
set(CMAKE_CXX_FLAGS "-D__ANDROID_API__=21 -DANDROID_STL=gnustl_static -fno-exceptions -O2 -fpie -fpic -fPIE -fPIC -pie -std=c++11 -lm -lstdc++ -Wl,-llog" CACHE STRING "" FORCE)