#include "opencv2/core/core_c.h"
Old C data structures and arithmetic routines
#include "opencv2/core/core.hpp"
New C++ data structures and arithmetic routines
#include "opencv2/flann/miniflann.hpp"
Approximate nearest neighbor matching functions
#include "opencv2/imgproc/imgproc_c.h"
Old C image processing functions
#include "opencv2/imgproc/imgproc.hpp"
New C++ image processing functions
#include "opencv2/video/photo.hpp"
Algorithms specific to handling and restoring photographs
#include "opencv2/video/video.hpp"
Video tracking and background segmentation routines
#include "opencv2/features2d/features2d.hpp"
Two-dimensional feature tracking support
#include "opencv2/objdetect/objdetect.hpp"
Cascade face detector; latent SVM; HoG; planar patch detector
#include "opencv2/calib3d/calib3d.hpp"
Calibration and stereo
#include "opencv2/ml/ml.hpp"
Machine learning: clustering, pattern recognition
#include "opencv2/highgui/highgui_c.h"
Old C image display, sliders, mouse interaction, I/O
#include "opencv2/highgui/highgui.hpp"
New C++ image display, sliders, buttons, mouse, I/O
#include "opencv2/contrib/contrib.hpp"
User-contributed code: flesh detection, fuzzy mean-shift tracking, spin images,self-similar features
You may use the include file opencv.hpp to include any and every possible OpenCV function, but it will slow down compile time. If you are using only, say, image processing functions, compile time will be faster if you include only opencv2/imgproc/imgproc.hpp.
来源：oschina
链接：https://my.oschina.net/u/4408322/blog/4794458