The Core Functionality10(File Input and Output using XML and YAML files )

Goal

You'll find answers for the following questions:

How to print and read text entries to a file and OpenCV using YAML or XML files?
如何使用YAML或XML文件将文本条目打印并读取到文件和OpenCV？
How to do the same for OpenCV data structures?
如何为OpenCV数据结构做同样的事情？
How to do this for your data structures?
如何为你的数据结构做到这一点？
Usage of OpenCV data structures such as cv::FileStorage , cv::FileNode or cv::FileNodeIterator .
使用OpenCV数据结构，如cv :: FileStorage，cv :: FileNode或cv :: FileNodeIterator。

Source code

#include <opencv2/core.hpp>
#include <iostream>
#include <string>
using namespace cv;
using namespace std;
//help imformation
//static void help(char** av)
//{
//    cout << endl
//        << av[0] << " shows the usage of the OpenCV serialization functionality."         << endl
//        << "usage: "                                                                      << endl
//        << av[0] << " outputfile.yml.gz"                                                 << endl
//        << "The output file may be either XML (xml) or YAML (yml/yaml). You can even compress it by "
//        << "specifying this in its extension like xml.gz yaml.gz etc... "                  << endl
//        << "With FileStorage you can serialize objects in OpenCV by using the << and >> operators" << endl
//        << "For example: - create a class and have it serialized"                         << endl
//        << "             - use it to read and write matrices."                            << endl;
//}

//data structure define self
class MyData
{
public:
    MyData() : A(0), X(0), id()
    {}
    explicit MyData(int) : A(97), X(CV_PI), id("mydata1234") // explicit to avoid implicit conversion
    {}
    void write(FileStorage& fs) const                        //Write serialization for this class
    {
        fs << "{" << "A" << A << "X" << X << "id" << id << "}";
    }
    void read(const FileNode& node)                          //Read serialization for this class
    {
        A = (int)node["A"];
        X = (double)node["X"];
        id = (string)node["id"];
    }
public:   // Data Members
    int A;
    double X;
    string id;
};

//These write and read functions must be defined for the serialization in FileStorage to work
static void write(FileStorage& fs, const std::string&, const MyData& x)
{
    x.write(fs);
}
static void read(const FileNode& node, MyData& x, const MyData& default_value = MyData()){
    if(node.empty())
        x = default_value;
    else
        x.read(node);
}
// This function will print our custom class to the console
//重新定义<<符号
static ostream& operator<<(ostream& out, const MyData& m)
{
    out << "{ id = " << m.id << ", ";
    out << "X = " << m.X << ", ";
    out << "A = " << m.A << "}";
    return out;
}
int main()
{
//    if (ac != 2)
//    {
//        help(av);
//        return 1;
//    }
    string filename = "test.yaml";
    { //write
        Mat R = Mat_<uchar>::eye(3, 3),
            T = Mat_<double>::zeros(3, 1);
        MyData m(1);
        FileStorage fs(filename, FileStorage::WRITE);
        fs << "iterationNr" << 100;
        //注意其[]
        fs << "strings" << "[";                              // text - string sequence
        fs << "image1.jpg" << "Awesomeness" << "../data/baboon.jpg";
        fs << "]";                                           // close sequence
        //注意{}
        fs << "Mapping";                              // text - mapping
        fs << "{" << "One" << 1;
        fs <<        "Two" << 2 << "}";
        fs << "R" << R;                                      // cv::Mat
        fs << "T" << T;
        fs << "MyData" << m;                                // your own data structures
        fs.release();                                       // explicit close
        cout << "Write Done." << endl;
    }
    {//read
        cout << endl << "Reading: " << endl;
        FileStorage fs;
        fs.open(filename, FileStorage::READ);
        int itNr;
        //fs["iterationNr"] >> itNr;
        itNr = (int) fs["iterationNr"];
        cout << itNr << endl;
        if (!fs.isOpened())
        {
            cerr << "Failed to open " << filename << endl;
            //help(av);
            return 1;
        }
        FileNode n = fs["strings"];                         // Read string sequence - Get node
        if (n.type() != FileNode::SEQ)
        {
            cerr << "strings is not a sequence! FAIL" << endl;
            return 1;
        }
        FileNodeIterator it = n.begin(), it_end = n.end(); // Go through the node
        for (; it != it_end; ++it)
            cout << (string)*it << endl;
        n = fs["Mapping"];                                // Read mappings from a sequence
        cout << "Two " << (int)(n["Two"]) << "; ";
        cout << "One " << (int)(n["One"]) << endl << endl;

        MyData m;
        Mat R, T;
        fs["R"] >> R;                                      // Read cv::Mat
        fs["T"] >> T;
        fs["MyData"] >> m;                                 // Read your own structure_
        cout << endl
            << "R = " << R << endl;
        cout << "T = " << T << endl << endl;
        cout << "MyData = " << endl << m << endl << endl;
        //Show default behavior for non existing nodes
        cout << "Attempt to read NonExisting (should initialize the data structure with its default).";
        fs["NonExisting"] >> m;
        cout << endl << "NonExisting = " << endl << m << endl;
    }
    cout << endl
        << "Tip: Open up " << filename << " with a text editor to see the serialized data." << endl;
    return 0;
}

Explanation

大部分东西都很简单，唯一需要解释的就是关于自定义的数据结构的读取。
//These write and read functions must be defined for the serialization in FileStorage to work
static void write(FileStorage& fs, const std::string&, const MyData& x)
{
    x.write(fs);
}
static void read(const FileNode& node, MyData& x, const MyData& default_value = MyData()){
    if(node.empty())
        x = default_value;
    else
        x.read(node);
}

这两个函数是persistence.hpp中需要的。

The Core Functionality10(File Input and Output using XML and YAML files )