ubuntu opencv 无法使用绝对路径

Ubuntu中使用了https://blog.youkuaiyun.com/qq_36486890/article/details/97511295
来配置opencv。
安装后直接用个g++编译器跑，
imread相对路径可以正常读取图片，绝对路径会报错：
OpenCV Error: Assertion failed (size.width>0 && size.height>0) in imshow, file /build/opencv-L2vuMj/opencv-3.2.0+dfsg/modules/highgui/src/window.cpp, line 304
terminate called after throwing an instance of ‘cv::Exception’
what(): /build/opencv-L2vuMj/opencv-3.2.0+dfsg/modules/highgui/src/window.cpp:304: error: (-215) size.width>0 && size.height>0 in function imshow

Aborted (core dumped)

原因: 是我太蠢
pwd命令
查看当前路径
发现路径不一样。ubuntu还是要熟练啊