G++ undefined references for libuvc and opencv2 - c++

Question

I'm trying to compile a C++ program which includes the libuvc.h header file and some more header files of opencv2.
The problem is, that I'm getting the following errors (undefinded references):
root#Raspi_DataHarvest:~/Schreibtisch# g++ UVCCameraHandler.cpp -I/usr/local/include/libuvc -I/usr/local/include/opencv2
/tmp/ccvQZdkd.o: In function `UVCCameraHandler::start(int, CameraProperties, int)':
UVCCameraHandler.cpp:(.text+0x164): undefined reference to `uvc_init'
UVCCameraHandler.cpp:(.text+0x184): undefined reference to `uvc_perror'
UVCCameraHandler.cpp:(.text+0x204): undefined reference to `uvc_get_device_descriptor'
UVCCameraHandler.cpp:(.text+0x334): undefined reference to `uvc_open'
UVCCameraHandler.cpp:(.text+0x354): undefined reference to `uvc_perror'
UVCCameraHandler.cpp:(.text+0x3a8): undefined reference to `uvc_get_stream_ctrl_format_size'
UVCCameraHandler.cpp:(.text+0x3e8): undefined reference to `uvc_get_stream_ctrl_format_size'
UVCCameraHandler.cpp:(.text+0x40c): undefined reference to `uvc_print_diag'
UVCCameraHandler.cpp:(.text+0x424): undefined reference to `uvc_print_stream_ctrl'
UVCCameraHandler.cpp:(.text+0x43c): undefined reference to `uvc_perror'
UVCCameraHandler.cpp:(.text+0x46c): undefined reference to `uvc_stream_open_ctrl'
UVCCameraHandler.cpp:(.text+0x48c): undefined reference to `uvc_stream_start_iso'
UVCCameraHandler.cpp:(.text+0x4a4): undefined reference to `uvc_perror'
/tmp/ccvQZdkd.o: In function `UVCCameraHandler::grabFramesGrayscale(cv::Mat&, cv::Mat&)':
UVCCameraHandler.cpp:(.text+0x5c8): undefined reference to `uvc_stream_get_frame'
/tmp/ccvQZdkd.o: In function `UVCCameraHandler::grabFramesColor(cv::Mat&, cv::Mat&)':
UVCCameraHandler.cpp:(.text+0x864): undefined reference to `uvc_stream_get_frame'
UVCCameraHandler.cpp:(.text+0x92c): undefined reference to `cv::cvtColor(cv::_InputArray const&, cv::_OutputArray const&, int, int)'
/tmp/ccvQZdkd.o: In function `UVCCameraHandler::uvcFindDevice(uvc_context*, uvc_device**, int, int, char const*, int)':
UVCCameraHandler.cpp:(.text+0xae0): undefined reference to `uvc_get_device_list'
UVCCameraHandler.cpp:(.text+0xb10): undefined reference to `uvc_get_device_descriptor'
UVCCameraHandler.cpp:(.text+0xd0c): undefined reference to `uvc_get_device_descriptor'
/tmp/ccvQZdkd.o: In function `UVCCameraHandler::setProperties(CameraProperties)':
UVCCameraHandler.cpp:(.text+0xfb0): undefined reference to `uvc_get_gain'
UVCCameraHandler.cpp:(.text+0xff8): undefined reference to `uvc_set_gain'
UVCCameraHandler.cpp:(.text+0x103c): undefined reference to `uvc_set_ae_mode'
UVCCameraHandler.cpp:(.text+0x1050): undefined reference to `uvc_set_exposure_abs'
UVCCameraHandler.cpp:(.text+0x1068): undefined reference to `uvc_set_ae_mode'
/tmp/ccvQZdkd.o: In function `cv::String::String(char const*)':
UVCCameraHandler.cpp:(.text._ZN2cv6StringC2EPKc[_ZN2cv6StringC5EPKc]+0x60): undefined reference to `cv::String::allocate(unsigned int)'
/tmp/ccvQZdkd.o: In function `cv::String::~String()':
UVCCameraHandler.cpp:(.text._ZN2cv6StringD2Ev[_ZN2cv6StringD5Ev]+0x14): undefined reference to `cv::String::deallocate()'
/tmp/ccvQZdkd.o: In function `cv::String::operator=(cv::String const&)':
UVCCameraHandler.cpp:(.text._ZN2cv6StringaSERKS0_[_ZN2cv6StringaSERKS0_]+0x30): undefined reference to `cv::String::deallocate()'
/tmp/ccvQZdkd.o: In function `cv::Mat::Mat(cv::Size_<int>, int, void*, unsigned int)':
UVCCameraHandler.cpp:(.text._ZN2cv3MatC2ENS_5Size_IiEEiPvj[_ZN2cv3MatC5ENS_5Size_IiEEiPvj]+0x140): undefined reference to `cv::error(int, cv::String const&, char const*, char const*, int)'
UVCCameraHandler.cpp:(.text._ZN2cv3MatC2ENS_5Size_IiEEiPvj[_ZN2cv3MatC5ENS_5Size_IiEEiPvj]+0x244): undefined reference to `cv::error(int, cv::String const&, char const*, char const*, int)'
/tmp/ccvQZdkd.o: In function `cv::Mat::~Mat()':
UVCCameraHandler.cpp:(.text._ZN2cv3MatD2Ev[_ZN2cv3MatD5Ev]+0x3c): undefined reference to `cv::fastFree(void*)'
/tmp/ccvQZdkd.o: In function `cv::Mat::operator=(cv::Mat const&)':
UVCCameraHandler.cpp:(.text._ZN2cv3MataSERKS0_[_ZN2cv3MataSERKS0_]+0x140): undefined reference to `cv::Mat::copySize(cv::Mat const&)'
/tmp/ccvQZdkd.o: In function `cv::Mat::create(int, int, int)':
UVCCameraHandler.cpp:(.text._ZN2cv3Mat6createEiii[_ZN2cv3Mat6createEiii]+0xc4): undefined reference to `cv::Mat::create(int, int const*, int)'
/tmp/ccvQZdkd.o: In function `cv::Mat::release()':
UVCCameraHandler.cpp:(.text._ZN2cv3Mat7releaseEv[_ZN2cv3Mat7releaseEv]+0x68): undefined reference to `cv::Mat::deallocate()'
/tmp/ccvQZdkd.o: In function `cv::Mat::operator()(cv::Rect_<int> const&) const':
UVCCameraHandler.cpp:(.text._ZNK2cv3MatclERKNS_5Rect_IiEE[_ZNK2cv3MatclERKNS_5Rect_IiEE]+0x24): undefined reference to `cv::Mat::Mat(cv::Mat const&, cv::Rect_<int> const&)'
collect2: error: ld returned 1 exit status
So, this looks to me like g++ does not find the location of the header files, but they are installed in the correct directory!
root#Raspi_DataHarvest:~# find / | grep libuvc.h
/usr/local/include/libuvc/libuvc.h
root#Raspi_DataHarvest:~# find / | grep opencv2/opencv.hpp
/usr/local/include/opencv2/opencv.hpp
Furthermore, there's no effect using the absolute paths, like:
#include "/usr/local/include/libuvc.h"
...
Does anyone know how to solve the reference errors?

Answer 1

Try
g++ UVCCameraHandler.cpp -I/usr/local/include/libuvc -I/usr/local/include/opencv2 -luvc -lopencv
The most preferable
g++ UVCCameraHandler.cpp `pkg-config --libs --cflags opencv` `pkg-config --libs --cflags lubuvc`

Answer 2

Building a C++ program is a three-step process:
Editing the source
Compiling the source files into object files
Linking the object files into the final executable
Modern compilers often use front-end programs (like e.g. GCC with the g++ program) that combine steps 2 and 3 into a single action.
In step 2 above, the header files are included.
In step 3 you need to link with the actual libraries. You do not do this, so the linker will complain that it can't find the functions you use.
Linking with the libraries using GCC is done with the -l (lower-case L) option, listing the library name. Like for example -lopencv to link with the OpenCV library.
If the libraries are in a non-standard location (which /usr/local/lib usually is) then you need to tell the linker where to find the libraries as well. This is done with the -L option, similar to the -I option you already use to tell the compiler where to search for header-files. For example -L/usr/local/lib.

Answer 3

You need to link against the correct libraries (assuming your libs are in /usr/local/lib):
g++ UVCCameraHandler.cpp -I/usr/local/include/libuvc -I/usr/local/include/opencv2 -L/usr/local/lib -luvc -lopencv_core