由于未定义引用，无法获取要编译的OpenCV

这是一个链接器问题。尝试：

g++ -o test_1 test_1.cpp `pkg-config opencv --cflags --libs`

这应该可以编译源代码。然而，如果您最近从源代码编译了OpenCV，您将在运行时遇到链接问题，库将找不到。在大多数情况下，在从源代码编译库之后，您最终需要执行以下操作：

sudo ldconfig

我已经尝试了所有的解决方案。评论中的-lopencv_core -lopencv_imgproc -lopencv_highgui解决了我的问题。现在我的命令行在geany中看起来是这样的：

g++ -lopencv_core -lopencv_imgproc -lopencv_highgui  -o "%e" "%f"

当我建立：

g++ -lopencv_core -lopencv_imgproc -lopencv_highgui  -o "opencv" "opencv.cpp" (in directory: /home/fedora/Desktop/Implementations)

标题为：

#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"

遵循本教程。我在bash中运行了install-opencv.sh文件。它在教程中

从openCV 中读取示例

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;
}

在linux mint 17 中测试

如果有人仍然有这个问题。一种解决方案是使用MinGW重建源OpenCV库，而不使用OpenCV提供的二进制文件。我做到了，它就像一种魅力。

在linux中编译opencv4后，我也出现了同样的错误。

我不得不在我的.cpp文件之后链接库，而不是以前。

g++ $(pkg-config opencv4 --cflags) -std=c++17 foo.cpp $(pkg-config opencv4 --libs) -o foo.o

注意：我还将-D OPENCV_GENERATE_PKGCONFIG=ON传递给了cmake命令，以生成pkgconfig/opencv4.pc文件——pkg config命令需要它。

请阅读此处了解为什么顺序很重要的更多信息：为什么库链接的顺序有时会导致GCC中的错误？

如果您执行以下操作，您将能够从opencv_INSTALL_PATH使用opencv构建。

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)

对我来说，这种类型的错误：

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&)'

意思是装载顺序，我必须像那样做-lTransform360 -lopencv_dnn345 -lopencv...，那个顺序。把它们放在一起也有帮助，不要一开始就把-lTransform360放在一起。。。或者你会得到，因为一些奇怪的原因：

undefined reference to `VideoFrameTransform_new'
undefined reference to `VideoFrameTransform_generateMapForPlane'

我刚刚更改了参数的位置：g++-o测试2.out测试2.cpp pkg-config opencv4 --cflags --libs

在我改变位置之前，我使用了g++pkg-config opencv4 --cflags --libs test2.cpp-o test2.out。

您可以尝试在terminal中运行pkg config opencv--cflags--libs，或者运行pkg config opencv4--cflags-libs，看看是否可以获得任何信息。