3.4.3 from today include/opencv2 directory only contains opencv.hpp

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"3.4.2 contained all the hpp files" are you sure ?check it

you're probably looking in the wrong place.

for the windows, prebuilt libs it would be: opencv\build\include, if you build it yourself, then it's opencv\build\install\include

on a linux system, you'll find the headers in /usr/local/include , after you run cmake && make && make install