c++ - 头文件中非静态成员函数的使用无效

Question

我是 C/C++ 的新手，遇到以下问题。作为可执行文件的一部分，我想使用 OpenCV 在图片上绘制一些矩形。为此，我定义了一个单独的头文件，以使 .cpp 可执行文件尽可能短。它看起来像这样:

typedef struct Rectangle {
    cv::Point startPoint;
    cv::Point endPoint;

};

class drawSpaces {

private:
    Mat img;
    int ix = 1;
    int iy = 1;
    std::list<Rectangle> rectList;

public:
//mouse callback function
    void drawRect(int event, int x, int y, int, void *param) {
        if (event == CV_EVENT_LBUTTONDOWN) {
           //Save first point of rect
            ix = x;
            iy = y;
        } else if (event == CV_EVENT_LBUTTONUP) {
            //Save 2nd point of rect
            cv::rectangle(img, Point(ix, iy), Point(x, y), cv::Scalar(0, 255, 0));
            Rectangle rect;
            rect.startPoint = Point(ix, iy);
            rect.endPoint = Point(x, y);
            rectList.push_back(rect);
            }
        }
    }


    int draw(Mat image) {
        img = image;
        if (img.empty()) {
            cout << "\nerror reading image" << endl;
            return -1;
        }
        namedWindow("Image", 1);
        imshow("Image", img);
        setMouseCallback("Image", drawRect);
        while (waitKey(20) != 27)  // wait until ESC is pressed
        {
            imshow("Image", img);
        }
        //save image with rectangles
        imwrite( "../pics/new_Image.jpg", img );
        return 0;
    }

};

我现在想在我的 main 中创建一个 drawSpaces 类的对象和一个 Mat 图像，然后在其上运行绘制以获得新图像。但是，在构建时，我收到错误消息 错误:无效使用非静态成员函数 setMouseCallback("Image", drawRect); 编译器指向 drawRect 函数。

我看过这个问题的其他答案，大多数人似乎建议将 drawRect 更改为静态。但我不希望我的 drawRect 函数具有静态函数的功能，即能够在不存在实际 drawSpaces 对象的情况下被调用。

感谢任何帮助，包括编码风格方面的帮助!

编辑:使用

setMouseCallback("Image", drawSpaces::drawRect);

也没有帮助。

Answer 1

环境:g++5.4(c++11) + OpenCV 3.3

setMouseCallback("Image", callback); 的回调函数应该始终是静态的。因此，您应该将函数更改为:

static void drawRect(int event, int x, int y, int, void *param)

然后你也应该修改你的类定义(一些C++相关的知识，你应该自己学习)才能编译成功。

---

我的结果:

---

//! 2017.12.22 23:13:58 CST
#include <iostream>
#include <opencv2/opencv.hpp>
using namespace std;
using namespace cv;

struct Rectangle {
    cv::Point startPoint;
    cv::Point endPoint;

};

class drawSpaces {
private:
    static Mat img;
    static int ix;
    static int iy;
    static std::list<Rectangle> rectList;

public:

    static void drawRect(int event, int x, int y, int, void *param) {
        if (event == CV_EVENT_LBUTTONDOWN) {
           //Save first point of rect
            ix = x;
            iy = y;
        } else if (event == CV_EVENT_LBUTTONUP) {
            //Save 2nd point of rect
            cv::rectangle(img, Point(ix, iy), Point(x, y), cv::Scalar(0, 255, 0), 1, LINE_AA);
            Rectangle rect;
            rect.startPoint = Point(ix, iy);
            rect.endPoint = Point(x, y);
            rectList.push_back(rect);
            }
        }

    int draw(Mat image) {
        img = image;
        if (img.empty()) {
            cout << "\nerror reading image" << endl;
            return -1;
        }
        namedWindow("Image", 1);
        imshow("Image", img);
        setMouseCallback("Image", drawRect);
        while (waitKey(20) != 27) {
            imshow("Image", img);
        }
        //save image with rectangles
        imwrite( "new_Image.jpg", img );
        return 0;
    }

};

int drawSpaces::ix =0;
int drawSpaces::iy =0;
Mat drawSpaces::img = Mat() ;
std::list<Rectangle> drawSpaces::rectList;



int main(){
    Mat img = imread("test.png");
    drawSpaces obj;
    obj.draw(img);

}