Cannot get OpenCV to compile because of undefined references? - c++

Question

The code is simple and is essentially straight from this tutorial. I am running Arch Linux and have the OpenCV library stored at /usr/include/. I have also checked to ensure that /usr/include is in my PATH.
#include <opencv/cv.h>
#include <opencv/highgui.h>
#include <iostream>
using namespace cv;
int main(int argc, char** argv){
Mat image;
Mat grayImage;
if(!argv[1]){
std::cerr << "No image data!" << std::endl;
return -1;
}
image = imread(argv[1], 1);
cvtColor(image, grayImage, CV_BGR2GRAY);
imwrite("Gray_Image.jpg", grayImage);
namedWindow(argv[1], CV_WINDOW_AUTOSIZE);
namedWindow("Gray Image", CV_WINDOW_AUTOSIZE);
imshow(argv[1], image);
imshow("Gray Image", grayImage);
waitKey(0);
return 0;
}
The compiler process successfully finds and include these header files, but I still get undefined reference errors at compile-time. If you look into the header files I included they further include other files in /usr/include/opencv2. I have checked and such header files do exist.
Any ideas?
/tmp/ccudBcqD.o: In function `main':
test.cpp:(.text+0xc0): undefined reference to `cv::imread(std::string const&, int)'
test.cpp:(.text+0x11f): undefined reference to `cv::_OutputArray::_OutputArray(cv::Mat&)'
test.cpp:(.text+0x138): undefined reference to `cv::_InputArray::_InputArray(cv::Mat const&)'
test.cpp:(.text+0x158): undefined reference to `cv::cvtColor(cv::_InputArray const&, cv::_OutputArray const&, int, int)'
test.cpp:(.text+0x180): undefined reference to `cv::_InputArray::_InputArray(cv::Mat const&)'
test.cpp:(.text+0x1ca): undefined reference to `cv::imwrite(std::string const&, cv::_InputArray const&, std::vector<int, std::allocator<int> > const&)'
test.cpp:(.text+0x241): undefined reference to `cv::namedWindow(std::string const&, int)'
test.cpp:(.text+0x291): undefined reference to `cv::namedWindow(std::string const&, int)'
test.cpp:(.text+0x2bf): undefined reference to `cv::_InputArray::_InputArray(cv::Mat const&)'
test.cpp:(.text+0x2ff): undefined reference to `cv::imshow(std::string const&, cv::_InputArray const&)'
test.cpp:(.text+0x32d): undefined reference to `cv::_InputArray::_InputArray(cv::Mat const&)'
test.cpp:(.text+0x361): undefined reference to `cv::imshow(std::string const&, cv::_InputArray const&)'
test.cpp:(.text+0x383): undefined reference to `cv::waitKey(int)'
/tmp/ccudBcqD.o: In function `cv::Mat::~Mat()':
test.cpp:(.text._ZN2cv3MatD2Ev[_ZN2cv3MatD5Ev]+0x39): undefined reference to `cv::fastFree(void*)'
/tmp/ccudBcqD.o: In function `cv::Mat::operator=(cv::Mat const&)':
test.cpp:(.text._ZN2cv3MataSERKS0_[_ZN2cv3MataSERKS0_]+0x111): undefined reference to `cv::Mat::copySize(cv::Mat const&)'
/tmp/ccudBcqD.o: In function `cv::Mat::release()':
test.cpp:(.text._ZN2cv3Mat7releaseEv[_ZN2cv3Mat7releaseEv]+0x47): undefined reference to `cv::Mat::deallocate()'
collect2: error: ld returned 1 exit status
[Finished in 1.1s with exit code 1]
[shell_cmd: g++ "/home/branden/Desktop/OpenCV/test.cpp" -o "/home/branden/Desktop/OpenCV/test"]
[dir: /home/branden/Desktop/OpenCV]
[path: /usr/local/sbin:/usr/local/bin:/usr/bin:/usr/bin/vendor_perl:/usr/bin/core_perl]

Answer 1

This is a linker issue. Try:
g++ -o test_1 test_1.cpp `pkg-config opencv --cflags --libs`
This should work to compile the source. However, if you recently compiled OpenCV from source, you will meet linking issue in run-time, the library will not be found.
In most cases, after compiling libraries from source, you need to do finally:
sudo ldconfig

Answer 2

I have tried all solutions. The -lopencv_core -lopencv_imgproc -lopencv_highgui in comments solved my problem. And now my command line looks like this in geany:
g++ -lopencv_core -lopencv_imgproc -lopencv_highgui -o "%e" "%f"
When I build:
g++ -lopencv_core -lopencv_imgproc -lopencv_highgui -o "opencv" "opencv.cpp" (in directory: /home/fedora/Desktop/Implementations)
The headers are:
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"

Answer 3

follow this tutorial. i ran the install-opencv.sh file in bash. its in the tutorial
read the example from openCV
CMakeLists.txt
cmake_minimum_required(VERSION 3.7)
project(openCVTest)
# cmake needs this line
cmake_minimum_required(VERSION 2.8)
# Define project name
project(opencv_example_project)
# Find OpenCV, you may need to set OpenCV_DIR variable
# to the absolute path to the directory containing OpenCVConfig.cmake file
# via the command line or GUI
find_package(OpenCV REQUIRED)
# If the package has been found, several variables will
# be set, you can find the full list with descriptions
# in the OpenCVConfig.cmake file.
# Print some message showing some of them
message(STATUS "OpenCV library status:")
message(STATUS " version: ${OpenCV_VERSION}")
message(STATUS " libraries: ${OpenCV_LIBS}")
message(STATUS " include path: ${OpenCV_INCLUDE_DIRS}")
if(CMAKE_VERSION VERSION_LESS "2.8.11")
# Add OpenCV headers location to your include paths
include_directories(${OpenCV_INCLUDE_DIRS})
endif()
# Declare the executable target built from your sources
add_executable(main main.cpp)
# Link your application with OpenCV libraries
target_link_libraries(main ${OpenCV_LIBS})
main.cpp
/**
* #file LinearBlend.cpp
* #brief Simple linear blender ( dst = alpha*src1 + beta*src2 )
* #author OpenCV team
*/
#include "opencv2/imgcodecs.hpp"
#include "opencv2/highgui.hpp"
#include <stdio.h>
using namespace cv;
/** Global Variables */
const int alpha_slider_max = 100;
int alpha_slider;
double alpha;
double beta;
/** Matrices to store images */
Mat src1;
Mat src2;
Mat dst;
//![on_trackbar]
/**
* #function on_trackbar
* #brief Callback for trackbar
*/
static void on_trackbar( int, void* )
{
alpha = (double) alpha_slider/alpha_slider_max ;
beta = ( 1.0 - alpha );
addWeighted( src1, alpha, src2, beta, 0.0, dst);
imshow( "Linear Blend", dst );
}
//![on_trackbar]
/**
* #function main
* #brief Main function
*/
int main( void )
{
//![load]
/// Read images ( both have to be of the same size and type )
src1 = imread("../data/LinuxLogo.jpg");
src2 = imread("../data/WindowsLogo.jpg");
//![load]
if( src1.empty() ) { printf("Error loading src1 \n"); return -1; }
if( src2.empty() ) { printf("Error loading src2 \n"); return -1; }
/// Initialize values
alpha_slider = 0;
//![window]
namedWindow("Linear Blend", WINDOW_AUTOSIZE); // Create Window
//![window]
//![create_trackbar]
char TrackbarName[50];
sprintf( TrackbarName, "Alpha x %d", alpha_slider_max );
createTrackbar( TrackbarName, "Linear Blend", &alpha_slider, alpha_slider_max, on_trackbar );
//![create_trackbar]
/// Show some stuff
on_trackbar( alpha_slider, 0 );
/// Wait until user press some key
waitKey(0);
return 0;
}
Tested in linux mint 17

Answer 4

if anyone still having this problem. One solution is to rebuild the source OpenCV library using MinGW and not use the binaries given by OpenCV. I did it and it worked like a charm.

Answer 5

I had the same error after compiling the opencv4 in linux.
I had to link the libraries after my .cpp files not before.
g++ $(pkg-config opencv4 --cflags) -std=c++17 foo.cpp $(pkg-config opencv4 --libs) -o foo.o
Note: I also passed -D OPENCV_GENERATE_PKGCONFIG=ON to the cmake command to generate the pkgconfig/opencv4.pc file - the pkg-config command needs it.
Read here for more info about why the order matters: Why does the order in which libraries are linked sometimes cause errors in GCC?

Answer 6

If you do the following, you will be able to use opencv build from OpenCV_INSTALL_PATH.
cmake_minimum_required(VERSION 2.8)
SET(OpenCV_INSTALL_PATH /home/user/opencv/opencv-2.4.13/release/)
SET(OpenCV_INCLUDE_DIRS "${OpenCV_INSTALL_PATH}/include/opencv;${OpenCV_INSTALL_PATH}/include")
SET(OpenCV_LIB_DIR "${OpenCV_INSTALL_PATH}/lib")
LINK_DIRECTORIES(${OpenCV_LIB_DIR})
set(OpenCV_LIBS opencv_core opencv_imgproc opencv_calib3d opencv_video opencv_features2d opencv_ml opencv_highgui opencv_objdetect opencv_contrib opencv_legacy opencv_gpu)
# find_package( OpenCV )
project(edge.cpp)
add_executable(edge edge.cpp)

Answer 7

For me, this type of error:
mingw-w64-x86_64/lib/gcc/x86_64-w64-mingw32/8.2.0/../../../../x86_64-w64-mingw32/bin/ld: mingw-w64-x86_64/x86_64-w64-mingw32/lib/libTransform360.a(VideoFrameTransform.cpp.obj):VideoFrameTransform.cpp:(.text+0xc7c):
undefined reference to `cv::Mat::Mat(cv::Mat const&, cv::Rect_<int> const&)'
meant load order, I had to do -lTransform360 -lopencv_dnn345 -lopencv... just like that, that order.
And putting them right next to each other helped too, don't put -lTransform360 all the way at the beginning...or you'll get, for some freaky reason:
undefined reference to `VideoFrameTransform_new'
undefined reference to `VideoFrameTransform_generateMapForPlane'
...

Answer 8

I just changed the position of paramters:
g++ -o test2.out test2.cpp pkg-config opencv4 --cflags --libs
Before I changed the position I used g++ pkg-config opencv4 --cflags --libs test2.cpp -o test2.out.
You can try to run pkg-config opencv --cflags --libs in terminal or run pkg-config opencv4 --cflags --libs to see if you can obtain any information.