OpenCV中的分段错误

问题描述

我最近开始使用C ++做一些图像处理工作，并且遇到了分割错误的问题。希望有人可以帮助我弄清楚发生了什么事？谢谢！！问题是，下面附加的代码可以正常工作，但是如果声明了“ vector roi_corners（4）;”，更改为“向量roi_corners;”然后使用“ push_back（）”和“ clear（）”来更新向量，将会得到分割错误。有人可以帮我弄清楚这个问题的原因吗？谢谢！！

OpenCV版本：4.4.0

MacOS版本：10.14.5

可行代码

#include <opencv2/opencv.hpp>
#include <iostream>
#include <math.h>
#include <vector>  

#define PI 3.14159265
#define WINDOW "Image Correction"

using namespace std;
using namespace cv;

vector< Point2f> roi_corners(4); 
vector< Point2f> dst_corners(4); 
Mat img1;
Mat cache;
int roi_id;

void On_mouse(int event,int x,int y,int flags,void*);


int main(int argc,char const *argv[])
{
    
    //import image
    roi_id = 0;
    img1 = imread("Board.jpg");
    if ( img1.empty() )
    {
        cerr << "Please Import an Image!!" << endl;
    }
    int factor = 60;//for pixel adjustment
    cache = img1.clone();//copy for retake points
    imshow(WINDOW,img1);
    
    
    /*Run the point taking procedure*/
    while(true){
     setMouseCallback(WINDOW,On_mouse,0);
     char c = (char)waitKey( 10 );
     if(c=='n') break;//press 'n' when determine the four point you want 
     if(c=='e') {roi_id=0; img1 = cache.clone();} //press 'e' to retake the foru point

    }
    

    /*For adjustment point estimation*/
    dst_corners[0].x = roi_corners[0].x;
    dst_corners[0].y = roi_corners[0].y;
    dst_corners[1].x = roi_corners[0].x+factor*1;
    dst_corners[1].y = roi_corners[0].y;
    dst_corners[2].x = roi_corners[0].x+factor*1;
    dst_corners[2].y = roi_corners[0].y+factor*1;
    dst_corners[3].x = roi_corners[0].x;
    dst_corners[3].y = roi_corners[0].y+factor*1;

    Mat M = getPerspectiveTransform(roi_corners,dst_corners);
    Mat warped_image;
    

    /*Print the corrected picture*/
    Size sz = cache.size();
    warpPerspective(cache,warped_image,M,Size(sz.width,sz.height)); // do perspective transformation
    imshow("Corrected Image",warped_image);
    waitKey(0);
    cout<<"complete"<<endl;
    return 0;
}


void On_mouse(int event,void*)
{   imshow(WINDOW,img1);
    if(roi_id<4){
        if (event == EVENT_LBUTTONDOWN){
            roi_corners[roi_id].x=x; 
            roi_corners[roi_id].y=y;
            cout<<"The Point You Take is: "<<x<<' '<<y<<endl;
            roi_id++;
            circle(img1,Point(x,y),2,Scalar(0,255),LINE_8,0);
            imshow(WINDOW,img1);
        }

    }

}

如果我这样修改代码，它将显示段错误

#include <opencv2/opencv.hpp>
#include <iostream>
#include <math.h>
#include <vector>  

#define PI 3.14159265
#define WINDOW "Image Correction"

using namespace std;
using namespace cv;

vector< Point2f> roi_corners; 
vector< Point2f> dst_corners; 
Mat img1;
Mat cache;


void On_mouse(int event,0);
     char c = (char)waitKey( 10 );
     if(c=='n') break;//press 'n' when determine the four point you want 
     if(c=='e') {roi_corner.clear(); img1 = cache.clone();} //press 'e' to retake the foru point

    }
    

    /*For adjustment point estimation*/
    dst_corners[0].x = roi_corners[0].x;
    dst_corners[0].y = roi_corners[0].y;
    dst_corners[1].x = roi_corners[0].x+factor*1;
    dst_corners[1].y = roi_corners[0].y;
    dst_corners[2].x = roi_corners[0].x+factor*1;
    dst_corners[2].y = roi_corners[0].y+factor*1;
    dst_corners[3].x = roi_corners[0].x;
    dst_corners[3].y = roi_corners[0].y+factor*1;

    Mat M = getPerspectiveTransform(roi_corners,img1);
    if(roi_corners.size()<4){
        if (event == EVENT_LBUTTONDOWN){
            roi_corners.push_back(Point2f(x,y)); 
            cout<<"The Point You Take is: "<<x<<' '<<y<<endl;
            circle(img1,img1);
        }

    }

}

解决方法

您的代码有两件事。您声明一个包含4个元素的向量，但不对其进行初始化。根据您的平台和数据类型，您可能会看到不希望的行为。尝试在同一行上声明和初始化向量：

std::vector<cv::Point2f> roi_corners( 4,cv::Point2f(0.0,0.0) );

当然，如果用初始容量（size）和初始值声明向量，则可以使用std::vector<>::operator[]索引每个元素：

roi_corners[0] = cv::Point2f( 1.0,2.0 );
roi_corners[1] = cv::Point2f( 3.0,4.0 );
roi_corners[2] = cv::Point2f( 5.0,6.0 );
roi_corners[3] = cv::Point2f( 7.0,8.0 );

通过声明具有初始大小的向量，您可以分配内存，该内存将用于store和load向量中的各个元素。现在，假设您不声明矢量的初始大小，而是使用push_back随便添加元素：

//vector declaration with no initial size:
std::vector<cv::Point2f> roi_corners;

//store a new element into the vector:
roi_corners.push_back( cv::Point2f(1.0,2.0) );

很酷，您的向量存储了一个新元素，并且仅显示一项的容量。但是，您仍然可以这样做：

roi_corners[0] = cv::Point2f( 1.0,2.0 ); // data overwrite in position 0
roi_corners[1] = cv::Point2f( 3.0,4.0 ); // you haven't allocated memory for this yet!

Result: seg fault

推论：如果您有大小为N的预定义矢量，则可以通过0将元素从N索引到std::vector<>::operator[] ，因为已分配内存以容纳所有N元素。如果您尝试处理超出此范围的元素，则会看到seg fault。