c++ - 在 C++ 中使用库时为 "Undefined reference to"

Question

在运行我在互联网上从 http://docs.opencv.org/doc/tutorials/objdetect/cascade_classifier/cascade_classifier.html 中找到的一些代码时，我遇到了以下问题:newmain.cpp:(.text+0x17): 对 `cv::VideoCapture::VideoCapture()' 的 undefined reference

newmain.cpp:(.text+0x35): 对 `cv::CascadeClassifier::load(std::string const&)' 的 undefined reference

newmain.cpp:(.text+0x5f): 对 `cv::CascadeClassifier::load(std::string const&)' 的 undefined reference

newmain.cpp:(.text+0x8e): 对 `cv::VideoCapture::open(int)' 的 undefined reference

newmain.cpp:(.text+0x9d): 对 `cv::VideoCapture::isOpened() const' 的 undefined reference

newmain.cpp:(.text+0x116): 对 `cv::waitKey(int)' 的 undefined reference

newmain.cpp:(.text+0x141): 对 `cv::VideoCapture::read(cv::Mat&)' 的 undefined reference

(列表继续但所有相同类型的错误)

代码应该从图片中检测面部和眼睛。

代码使用了我安装的opencv2中的一些函数:

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

    #include <iostream>
    #include <stdio.h>

    using namespace std;
    using namespace cv;

    /** Function Headers */
    void detectAndDisplay( Mat frame );

    /** Global variables */
    String face_cascade_name = "haarcascade_frontalface_alt.xml";
    String eyes_cascade_name = "haarcascade_eye_tree_eyeglasses.xml";
    CascadeClassifier face_cascade;
    CascadeClassifier eyes_cascade;
    String window_name = "Capture - Face detection";

    /** @function main */
    int main( void )
    {
        VideoCapture capture;
        Mat frame;

        //-- 1. Load the cascades
        if( !face_cascade.load( face_cascade_name ) ){ printf("--(!)Error loading face cascade\n"); return -1; };
        if( !eyes_cascade.load( eyes_cascade_name ) ){ printf("--(!)Error loading eyes cascade\n"); return -1; };

        //-- 2. Read the video stream
        capture.open( -1 );
        if ( ! capture.isOpened() ) { printf("--(!)Error opening video capture\n"); return -1; }

        while ( capture.read(frame) )
        {
            if( frame.empty() )
            {
                printf(" --(!) No captured frame -- Break!");
                break;
            }

            //-- 3. Apply the classifier to the frame
            detectAndDisplay( frame );

            int c = waitKey(10);
            if( (char)c == 27 ) { break; } // escape
        }
        return 0;
    }

    /** @function detectAndDisplay */
    void detectAndDisplay( Mat frame )
    {
        std::vector<Rect> faces;
        Mat frame_gray;

        cvtColor( frame, frame_gray, COLOR_BGR2GRAY );
        equalizeHist( frame_gray, frame_gray );

        //-- Detect faces
        face_cascade.detectMultiScale( frame_gray, faces, 1.1, 2, 0|CASCADE_SCALE_IMAGE, Size(30, 30) );

        for ( size_t i = 0; i < faces.size(); i++ )
        {
            Point center( faces[i].x + faces[i].width/2, faces[i].y + faces[i].height/2 );
            ellipse( frame, center, Size( faces[i].width/2, faces[i].height/2 ), 0, 0, 360, Scalar( 255, 0, 255 ), 4, 8, 0 );

            Mat faceROI = frame_gray( faces[i] );
            std::vector<Rect> eyes;

            //-- In each face, detect eyes
            eyes_cascade.detectMultiScale( faceROI, eyes, 1.1, 2, 0 |CASCADE_SCALE_IMAGE, Size(30, 30) );

            for ( size_t j = 0; j < eyes.size(); j++ )
            {
                Point eye_center( faces[i].x + eyes[j].x + eyes[j].width/2, faces[i].y + eyes[j].y + eyes[j].height/2 );
                int radius = cvRound( (eyes[j].width + eyes[j].height)*0.25 );
                circle( frame, eye_center, radius, Scalar( 255, 0, 0 ), 4, 8, 0 );
            }
        }
        //-- Show what you got
        imshow( window_name, frame );
    }

感谢您能给我的任何帮助!

Answer 1

看来，您没有链接到任何 opencv 库。

gcc objDetection.cpp -o objDetection -lopencv_core -lopencv_imgproc -lopencv_objdetect -lopencv_highgui