cmakelist 定义变量

自定义变量：

SET(opencv_dir "/mnt/d/android/OpenCV-3.4.8-android-sdk")

调用：

INCLUDE_DIRECTORIES(${opencv_dir}/sdk/native/jni/include)

SET(OpenCV_LIB ${opencv_dir}/sdk/native/libs/arm64-v8a/libopencv_java3.so)

打印出自定义变量：

语法：MESSAGE("include folder: "${include_dir})

在执行cmaek 命令的时候就会输入${include_dir}的值

判断变量用法：

判断字符，else用法，打印消息

if(address  STREQUAL "arm64-v8a")
    message("defined address!!!!!!!!!!")
else()
    message("NOT defined address!!!!!!!!!")
endif()
 
option(address "hello world" ON)
message("option is ${address}")
 
if(address)
    message("defi