写程序时要想下各种可能出错的情况，提前给出错误提示，项目大了就可以比较容易找错误。

比如，当特征点个数小于4时不能计算单应矩阵，所以当个数小于4时先输出提示：

if (matchePoints.size()>10)for (int i = 0; i<11; i++){imagePoints1.push_back(keypoints1[matchePoints[i].Idx1].pt);imagePoints2.push_back(keypoints2[matchePoints[i].Idx2].pt);}else if (matchePoints.size() > 4 )for (int i = 0; i < matchePoints.size(); i++){imagePoints1.push_back(keypoints1[matchePoints[i].Idx1].pt);imagePoints2.push_back(keypoints2[matchePoints[i].Idx2].pt);}else{cout << "特征点个数小于4" << endl;exit(1);}

再比如，动态申请指针指向的内存空间时，有可能出现内存申请不成功的情况，所以每次申请完都先判断是否申请成功：

double* wid = (double*)malloc((num+1) *sizeof(double));//存储每个矩形的宽  
if (wid == NULL)  
{  cout << "Fail to allocate memory to wid" << endl;  exit(1);  
}