find_package其實在windows下扮演的角色並不是很重要。在Unix下就非常重要了，find_package可以根據cmake內建的.cmake的指令碼去找相應的庫的模組，當然，內建了很多庫的模組變數，呼叫了find_package之後，會有相應的變數“生成”有效。

比如呼叫了find_package(Qt5Widgets)，find_package(Qt4 COMPONENTS QTCORE QTGUI QTOPENGL QTSVG)返回之後

就會有變數Qt5Widgets_FOUND，Qt5Widgets_INCLUDE_DIRS相應的變數生效。

然後就可以在CMakeLists.txt裡面使用上述的變量了。類似如下：

1 INCLUDE_DIRECTORIES(${QT_INCLUDES})
2 INCLUDE_DIRECTORIES(${Qt5Widgets_INCLUDE_DIRS})
3 INCLUDE_DIRECTORIES(${Qt5Svg_INCLUDE_DIRS})
4 INCLUDE_DIRECTORIES(${Qt5OpenGL_INCLUDE_DIRS})
5 INCLUDE_DIRECTORIES(${Qt5Concurrent_INCLUDE_DIRS})

1 if(Qt5Widgets_FOUND)
2 
3 
4 message(STATUS ${Qt5Widgets_INCLUDE_DIRS})
 
5    #qt5
6 else()
7  find_package(Qt4 REQUIRED)  #qt4
8  include(${QT_USE_FILE})
9 endif()

references:

http://qt-project.org/doc/qt-5/cmake-manual.html

http://blog.csdn.net/bowater/article/details/2477227

http://www.kdab.com/using-cmake-with-qt-5/