Error from "make" when enabling OpenCV 3

[GuidoBartoli]

Hi,
I'm using Linux Mint 18.3 64-bit (Ubuntu 16.04) with OpenCV 3.4.1 correctly configured and installed.
I just cloned the darknet repository and enabled OpenCV support in the Makefile setting OPENCV=1.
When issuing the make command, I receive this error:

mkdir -p obj mkdir -p results gcc -Iinclude/ -Isrc/ -DOPENCVpkg-config --cflags opencv -Wall -Wno-unknown-pragmas -Wfatal-errors -fPIC -Ofast -DOPENCV -c ./src/gemm.c -o obj/gemm.o In file included from /usr/local/include/opencv2/core/types_c.h:59:0, from /usr/local/include/opencv2/core/core_c.h:48, from /usr/local/include/opencv2/highgui/highgui_c.h:45, from include/darknet.h:25, from ./src/utils.h:5, from ./src/gemm.c:2: /usr/local/include/opencv2/core/cvdef.h:485:1: error: unknown type name ‘namespace’ namespace cv { ^ compilation terminated due to -Wfatal-errors. Makefile:85: recipe for target 'obj/gemm.o' failed make: *** [obj/gemm.o] Error 1

Which is strange, because namespace cv is used by almost every application based on OpenCV... What am I missing here? Is this OpenCV not compatible with Darknet?

Thanks,
Best regards

[MaeThird]

C API is not supported by the opencv official in their 3.4 version. As cited here:opencv/opencv#10941 and:opencv/opencv#10963

[AlexeyAB]

@GuidoBartoli There is C API bug in OpenCV 3.4.1.
Try to use OpenCV 3.4.0

[GuidoBartoli]

Yep, that works, thanks!

[beyhangl]

I'm using 3.4.0 but have this problem.

import cv2
cv2.version
'3.4.0'

[hikariakio]

Guys...sorry for question...how can i compile darknet with opencv 3.4.0 .. whenever I use brew install opencv , it gives me latest version of opencv (3.4.1)..

How can i use darknet with opencv3.4.0 in mac?

[evilmtv]

@hikariakio
I'm not too familiar with this but try this:
https://stackoverflow.com/questions/3987683/homebrew-install-specific-version-of-formula

[Firststep2014]

@AlexeyAB
Hello,I've used Opencv3.4.1,and my problem happens to be "error: unknown type name 'namespace'"

Does this mean to be same question?

[PeterQuinn925]

This is the same issue. Use the recommended version of OpenCV.