1.由于需要，之前系统中是opencv2.4.10版本，后来安装opencv3.10版本，并支持多版本切换。通过以下命令可以查看opencv版本
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1. pkg-config --modversion opencv
2.如果编译好并安装了opencv3.10版本，想切换到3.10版本，可以通过如下的方式，
通过修改bashrc文件来设置PKG_ CONFIG_PATH 和 LD_LIBRARY_PATH的路径来选择对应的opencv版本
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1. sudo gedit ~/.bashrc
并在文件的默认追加新编译的3.10版本的路径，也就是cmake时：CMAKE_INSTALL_PREFIX=/usr/local/opencv/3.10
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1. export PKG_CONFIG_PATH=/usr/local/opencv/3.10/lib/pkgconfig
2. export LD_LIBRARY_PATH=/usr/local/opencv/3.10/lib
然后执行命令，后面用pkg-config --modversion opencv 查看opencv版本的时候就是3.10版本
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1. source ~/.bashrc
3.上面的这些过程并不能保证在写makefile中调用的是3.10版本的库，可能还是调用之前的2.4.10的库，具体还是要在CMakeList.txt中指定要找的opencv的目录，
bashrc文件和CMakeList.txt文件中修改的内容改成对应的opencv2.4.10的位置就好了。
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1. # cmake needs this line
2. cmake_minimum_required(VERSION 2.8)
3. set (OpenCV_DIR "/usr/local/opencv-3.1.0/build")
4. # Define project name
5. project(myTest)
6. # Find OpenCV, you may need to set OpenCV_DIR variable
7. # to the absolute path to the directory containing OpenCVConfig.cmake file
8. # via the command line or GUI
9. find_package(OpenCV REQUIRED)
10. # If the package has been found, several variables will
11. # be set, you can find the full list with descriptions
12. # in the OpenCVConfig.cmake file.
13. # Print some message showing some of them
14. message(STATUS "OpenCV library status:")
15. message(STATUS " version: ${OpenCV_VERSION}")
16. message(STATUS " libraries: ${OpenCV_LIBS}")
17. message(STATUS " include path: ${OpenCV_INCLUDE_DIRS}")
18. if(CMAKE_VERSION VERSION_LESS "2.8.11")
19. # Add OpenCV headers location to your include paths
20. include_directories(${OpenCV_INCLUDE_DIRS})
21. endif()
22. # Declare the executable target built from your sources
23. add_executable(demo demo.cpp)
24. # Link your application with OpenCV libraries
25. target_link_libraries(demo ${OpenCV_LIBS})
【注意事项】
1、find_package(OpenCV REQUIRED)中的OpenCV一定要遵循该大小写。
因为该句话是根据OpenCV作为前缀自动去/usr/local/share/OpenCV（如果你的opencv安装时，默认前缀设置为：/usr/local时）文件夹中去找OpenCVConfig.cmake，OpenCV-config.cmake 两个文件，进而确定你要引入的opencv头文件和库函数在哪里。
2、自定义引入相应opencv版本
如果你有很多的opencv版本，尤其是一个是opencv2.x.x一个是opencv3.x.x，因为2和3在数据结构上有相对较大的变化，所以如果引入错误的版本可能导致程序的无法运行。因为find_package找默认路径下的OpenCV，但是很多时候安装多个版本的库的时候都会make install在opt目录下。、
安装在opt的文件中会有share文件夹，这里面就有咱们需要的ＯｐenCV文件夹，所以如果要自己有选择的控制版本，则在find_package这句话前面去设置opencv的ＯpenCV文件夹在哪里，添加set(OpenCV_DIR /opt/opencv-2.4.11/share/OpenCV)这句话。因为我的opencv2.4.11版本install在/opt/opencv-2.4.11文件夹下。这个可以根据你install的位置去变化。
cmake_minimum_required(VERSION 2.8)
project( DisplayImage )
#链接opencv2
set(OpenCV_DIR /usr/local/share/OpenCV)
find_package(OpenCV REQUIRED)
INCLUDE_DIRECTORIES(${OpenCV_INCLUDE_DIRS})
# 添加头文件
include_directories( ${OpenCV_INCLUDE_DIRS} )
message(STATUS "OpenCV library status:")
message(STATUS " version: ${OpenCV_VERSION}")
message(STATUS " libraries: ${OpenCV_LIBS}")
message(STATUS " include path: ${OpenCV_INCLUDE_DIRS}")
add_executable( DisplayImage DisplayImage.cpp )
target_link_libraries( DisplayImage ${OpenCV_LIBS} )
