Cmake中的find_package功能

find_package其实在windows下扮演的角色并不是很重要。在Unix下就非常重要了，find_package可以根据cmake内置的.cmake的脚本去找相应的库的模块，当然，内建了很多库的模块变量，调用了find_package之后，会有相应的变量“生成”有效。

比如调用了find_package(Qt5Widgets)，find_package(Qt4 COMPONENTS QTCORE QTGUI QTOPENGL QTSVG)返回之后

就会有变量Qt5Widgets_FOUND，Qt5Widgets_INCLUDE_DIRS相应的变量生效。

然后就可以在CMakeLists.txt里面使用上述的变量了。类似如下：

 INCLUDE_DIRECTORIES(${QT_INCLUDES})
 INCLUDE_DIRECTORIES(${Qt5Widgets_INCLUDE_DIRS})
 INCLUDE_DIRECTORIES(${Qt5Svg_INCLUDE_DIRS})
 INCLUDE_DIRECTORIES(${Qt5OpenGL_INCLUDE_DIRS})
 INCLUDE_DIRECTORIES(${Qt5Concurrent_INCLUDE_DIRS})

 if(Qt5Widgets_FOUND)

 message(STATUS ${Qt5Widgets_INCLUDE_DIRS})
    #qt5
 else()
  find_package(Qt4 REQUIRED)  #qt4
  include(${QT_USE_FILE})
 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/