codeblocks's undefined reference to 'cv::waitKey of int'

Undefined reference to 'cv::waitKey(int)'

I always thought it was the reason of C++11 or g++ version. I see:

http://forum.ubuntu.com.cn/viewtopic.php?f=48 & t = 377522 is put forward:

g++ `pkg-config --cflags --libs opencv` lena.cpp -o lena

This will fail to compile, while

g++ lena.cpp `pkg-config --cflags --libs opencv` -o lena

It will be successful. I tried 1 and sure enough it was.