CMake找不到OpenCV库。

Question

与此问题类似，我在OS X 10.10.3上使用OpenCV和CMake时遇到了麻烦。

经过一番努力，我终于成功地在我的系统上构建了OpenCV 3.0 beta；头文件现在位于/usr/local/include，库也像应该的那样在/usr/local/lib中。我有小程序使用了OpenCV，我的CMakeLists.txt看起来像这样：

set( CMAKE_CXX_FLAGS         "-O3 -w" ) 
find_package( OpenCV REQUIRED )
if(OpenCV_FOUND)
   message("Found OpenCV")
   message("Includes: " ${OpenCV_INCLUDE_DIRS})
endif(OpenCV_FOUND)

add_executable( cannyDetector canny/canny.cpp )

target_link_libraries( cannyDetector ${OpenCV_LIBS} )

I get the usual

Undefined symbols for architecture x86_64:
  "vtable for cv::_InputArray", referenced from:
      _main in correctImage.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
  "vtable for cv::_OutputArray", referenced from:
      _main in correctImage.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status
make[2]: *** [correctImage] Error 1
make[1]: *** [CMakeFiles/correctImage.dir/all] Error 2
make: *** [all] Error 2

变量OpenCV_LIBS包含的是：

opencv_xphoto;opencv_xobjdetect;opencv_ximgproc;opencv_xfeatures2d;opencv_tracking;opencv_text;opencv_surface_matching;opencv_saliency;opencv_rgbd;opencv_reg;opencv_optflow;opencv_line_descriptor;opencv_latentsvm;opencv_ccalib;opencv_bioinspired;opencv_bgsegm;opencv_adas;opencv_videostab;opencv_videoio;opencv_video;opencv_ts;opencv_superres;opencv_stitching;opencv_shape;opencv_photo;opencv_objdetect;opencv_ml;opencv_imgproc;opencv_imgcodecs;opencv_highgui;opencv_hal;opencv_flann;opencv_features2d;opencv_core;opencv_calib3d

此外，手动编译也可以运行：

gcc -o canny $(pkg-config --cflags opencv3)  $(pkg-config --libs opencv3) -lstdc++ -w -O3  ../canny/canny.cpp

我不知道为什么必须指定-lstdc++，但是如果没有它，链接会因为其他原因失败。

当运行make VERBOSE=1时，以下命令将用于可执行文件：

/opt/local/bin/g++   -O3 -w -lstdc++ -Wl,-search_paths_first -Wl,-headerpad_max_install_names  CMakeFiles/cannyDetector.dir/canny/canny.o  -o cannyDetector  /usr/local/lib/libopencv_xphoto.3.0.0.dylib /usr/local/lib/libopencv_ximgproc.3.0.0.dylib /usr/local/lib/libopencv_tracking.3.0.0.dylib /usr/local/lib/libopencv_text.3.0.0.dylib /usr/local/lib/libopencv_surface_matching.3.0.0.dylib /usr/local/lib/libopencv_saliency.3.0.0.dylib /usr/local/lib/libopencv_rgbd.3.0.0.dylib /usr/local/lib/libopencv_reg.3.0.0.dylib /usr/local/lib/libopencv_optflow.3.0.0.dylib /usr/local/lib/libopencv_line_descriptor.3.0.0.dylib /usr/local/lib/libopencv_latentsvm.3.0.0.dylib /usr/local/lib/libopencv_ccalib.3.0.0.dylib /usr/local/lib/libopencv_bioinspired.3.0.0.dylib /usr/local/lib/libopencv_bgsegm.3.0.0.dylib /usr/local/lib/libopencv_adas.3.0.0.dylib /usr/local/lib/libopencv_videostab.3.0.0.dylib /usr/local/lib/libopencv_ts.a /usr/local/lib/libopencv_superres.3.0.0.dylib /usr/local/lib/libopencv_stitching.3.0.0.dylib /usr/local/lib/libopencv_photo.3.0.0.dylib /usr/local/lib/libopencv_objdetect.3.0.0.dylib /usr/local/lib/libopencv_hal.a /usr/local/lib/libopencv_xobjdetect.3.0.0.dylib /usr/local/lib/libopencv_xfeatures2d.3.0.0.dylib /usr/local/lib/libopencv_shape.3.0.0.dylib /usr/local/lib/libopencv_video.3.0.0.dylib /usr/local/lib/libopencv_calib3d.3.0.0.dylib /usr/local/lib/libopencv_features2d.3.0.0.dylib /usr/local/lib/libopencv_ml.3.0.0.dylib /usr/local/lib/libopencv_highgui.3.0.0.dylib /usr/local/lib/libopencv_videoio.3.0.0.dylib /usr/local/lib/libopencv_imgcodecs.3.0.0.dylib /usr/local/lib/libopencv_imgproc.3.0.0.dylib /usr/local/lib/libopencv_flann.3.0.0.dylib /usr/local/lib/libopencv_core.3.0.0.dylib /usr/local/lib/libopencv_hal.a -framework AGL -framework OpenGL /usr/local/share/OpenCV/3rdparty/lib/libippicv.a

但是，如果我使用命令并将输入文件CMakeFiles/cannyDetector.dir/canny/canny.o替换为输入源文件../canny/canny.cpp，它就可以工作了！

所以库都在那里，但它仍然无法编译，因为编译器无法链接对象文件，但一步编译和链接却可以工作。

有人能否建议这里发生了什么？

- oarfish

---

使用 make VERBOSE=yes 命令获取详细输出，了解 cmake 如何调用编译器。 - arved

дҢ еЏҮиѓҢе·Із»ЏдҢүз”Ёlibstdc++зә–иҮ‘дғ†OpenCVеғ“пәЊиЂЊCMakeеЏҮиѓҢж­ӘиҮ•е›ңдҢүз”Ёlibc++гЂ‚е»ғи®®пәље°қиҮ•ењЁCMake文件中添加set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -stdlib=libstdc++")гЂ‚ - kiranpradeep

@Kiran，你说得没错，这个标志确实是必需的，但它的缺失并不会导致错误，而是因为CMake无法找到在usr/local/lib中的库。 - oarfish

请添加 message("OpenCV_LIBS=${OpenCV_LIBS}") 并发布输出。检查是否成功构建了 highgui：有时在 OpenCV 中禁用库（例如由于某些缺失的第三方库）并不那么明显。此外，如果您运行 make VERBOSE=1，您可以看到实际的链接器命令行。 - Antonio

我已经更新了问题，以反映编译库后我得到的最新错误变化。@Antonio 这绝对不是特定库的问题，它们都已经构建并准备好了。 - oarfish

Answer 1

在我的情况下，解决方法是指示CMake查找OpenCV配置模块的位置。

find_package(OpenCV REQUIRED PATHS /usr/local/share/OpenCV NO_DEFAULT_PATH) # manual specification of the OpenCVConfig.cmake path is necessary since otherwise, cmake assigns /opt/local a higher priority and ocv2.4 will be used

由于某些原因，/opt/local/share 的优先级比 /usr/local/share 更高，因此只找到了 OpenCV 2.4 的配置文件，但我使用的是 3.0 版本。我不确定是什么原因导致链接错误，但可能是因为在版本 3.0 中，一些代码从库移动到头文件中，必须与用户代码一起编译，但没有被包括进 CMake 中的版本 2 头文件中。

另外，

include_directories(${OpenCV_INCLUDE_DIRS})

丢失了。

- oarfish

Answer 2

在MacOS上，我们从端口安装OpenCV，然后只需将以下行添加到CmakeLists.txt文件中：

include("/System/Volumes/Data/opt/local/libexec/opencv4/cmake/OpenCVConfig.cmake")
target_include_directories(${A_PROJECT_NAME} PUBLIC ${OpenCV_INCLUDE_DIRS})
target_link_libraries(${A_PROJECT_NAME} ${OpenCV_LIBS})

- Alexandr Kirilov