opencv 为啥这个变量的值在函数里面是对的，传出来就出错了呢

Question

#include <iostream>
#include<opencv2\opencv.hpp>
#include<vector>
using namespace std;
using namespace cv;
#define PI 3.1415926535

double standardRad(double t) {
    double TWOPI = 2.0 * PI;
    if (t >= 0)
    {
        t = fmod(t + PI, TWOPI) - PI;
    }
    else
    {
        t = fmod(t - PI, -TWOPI) + PI;
    }
    cout << "standardRad(t):" << t << endl;
    return t;
}
Mat wRo_to_euler(Mat wRo) {
    cout << "wRo: " << wRo << endl;
    double yaw = standardRad(atan2(wRo.at<double>(1, 0), wRo.at<double>(0, 0)));
    double c = cos(yaw);
    double s = sin(yaw);
    double pitch = standardRad(atan2(-wRo.at<double>(2, 0),
        wRo.at<double>(0, 0)*c + wRo.at<double>(1, 0)*s)) / PI * 180;

    double roll = standardRad(atan2(wRo.at<double>(0, 2) * s - wRo.at<double>(1, 2)*c,
        -wRo.at<double>(0, 1)*s + wRo.at<double>(1, 1)*c)) / PI * 180;
    cout << "pitch: " << pitch << endl;
    cout << "roll: " << roll << endl;
    double returnWro_arr[3];
    returnWro_arr[0] = roll;
    returnWro_arr[1] = pitch;
    returnWro_arr[2] = yaw / PI * 180;
    Mat returnWro = Mat(1, 3, CV_64F, returnWro_arr);

    cout << "returnWro: " << returnWro << endl;
    /*cout << "returnWro.rows: "<<returnWro.rows << endl;
    cout << "returnWro.cols: "<<returnWro.cols << endl;*/

    return returnWro;    //returnWro的x,y,z坐标
}
int main()
{
    /*double h_arr[3][3] = { -0.01806375821938705, 0.9813313999097074, -0.1915334800712387,
    -0.9997671236683783, -0.01481447609281841, 0.01505010620015893,
    -0.01806375821938705, 0.1917530047987496, 0.9813706844588156 };
    Mat h = Mat(3, 3, CV_64F, h_arr);*/
    Mat h = (Mat_<double>(3, 3) << -0.01806375821938705, 0.9813313999097074, -0.1915334800712387,
        -0.9997671236683783, -0.01481447609281841, 0.01505010620015893,
        -0.01806375821938705, 0.1917530047987496, 0.9813706844588156);
    cout << "h: " << h << endl;
    //Mat temp = Mat(1, 3, CV_64F) ;
    Mat temp;
    temp = wRo_to_euler(h).clone();
    //cout << "temp.rows: " << temp.rows << endl;
    //cout << "temp.cols: " << temp.cols << endl;

    cout << "wRo_to_euler(h): "<<temp<< endl;
    system("pause");
}

这是运行结果

Answer 1

这就是把临时变量的引用return的结果。returnWro相当于函数内部的临时变量，如果编译器帮你保留的话，这个结果就是正确的，如果不帮你保留，那么结果就是错误的。举个例子来说

int& fun()
{
    int i = 1;
    return i;
}
int main(){
    int& a = fun();
    cout << a << endl;
    cout << a << endl;
    cout << a << endl;

}

上面代码的结果，你可以看到并非你想象的那样，每次都是1，而这就是编译器只帮你做了一次保留的结果，如果有些编译器没有做保留，每次都是乱码都有可能。
而你的问题就是相当于把临时变量的引用返回了，所以就出现了这个问题。有两种方法，一种是外部传入mat引用(推荐)

int wRo_to_euler(Mat wRo,Mat &outImg) {
  outImg=Mat(1, 3, CV_64F, returnWro_arr);
  return 0;
}
//调用：
Mat temp;
 wRo_to_euler(h，temp);

另外一种就是return Mat.clone();但是不推荐这种写法，安全性不高

Mat wRo_to_euler(Mat wRo) {
    return returnWro.clone();    //returnWro的x,y,z坐标
}