编译Darknet（YOLO目标检测）时遭遇OpenCV相关编译致命错误

Hey there, let's work through this Darknet compilation issue with your OpenCV setup. First, let's look at the error you ran into:

gcc -Iinclude/ -Isrc/ -DOPENCV pkg-config --cflags opencv -DGPU -I/usr/local/cuda-9.1/include/ -Wall -Wno-unused-result -Wno-unknown-pragmas -Wfatal-errors -fPIC -Ofast -DOPENCV -DGPU -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...

This points to a header file resolution issue between Darknet and your OpenCV 3.4.0 installation. Here's how to fix it, plus key notes for OpenCV 4.x+ users:

For OpenCV 3.4.0 Users #

• Verify pkg-config is targeting the right OpenCV version
  Sometimes system-wide pkg-config might be pointing to an older OpenCV install by mistake. Run this to check:

  pkg-config --modversion opencv
  

  If it doesn't return 3.4.0, force it to use your compiled version by setting the pkg-config path:

  export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig
  

  (Adjust the path if you installed OpenCV to a custom directory.)

• Tweak the Darknet Makefile
  Open the Makefile in your Darknet root folder and make these changes:

  1. Ensure OPENCV=1 is uncommented (it looks like you have -DOPENCV enabled, but double-check the Makefile's top-level config).
  2. Replace the pkg-config --cflags opencv call with either pkg-config --cflags opencv3 (some systems name OpenCV 3's config this way) or manually specify the header paths:

     CPPFLAGS+= -I/usr/local/include/opencv2 -I/usr/local/include
     

  3. Update the linker flags to explicitly link OpenCV libraries:

     LDFLAGS+= -L/usr/local/lib -lopencv_core -lopencv_highgui -lopencv_imgproc -lopencv_imgcodecs
     

• Clean and recompile
  Wipe old build artifacts first to avoid conflicts:

  make clean
  

  Then start the compile again:

  make
  

Critical Notes for OpenCV 4.x+ Users #

If you ever upgrade to OpenCV 4 or later, C++11 support is mandatory—skip this and you'll hit fatal compilation errors. Here's how to add it:

• Edit the Darknet Makefile to add -std=c++11 (or higher, like -std=c++14) to your compiler flags:

  CFLAGS+= -std=c++11
  

• Also, note that OpenCV 4's pkg-config config is usually named opencv4, so update the Makefile's pkg-config calls from opencv to opencv4 to pull the correct headers and libraries.

内容的提问来源于stack exchange，提问作者FlavienRJ