opencv自带例子学习-文件输入与输出

//包含头文件
#include <opencv2/core.hpp>
#include <iostream>
#include <string>

//使用命名空间，不建议这么做，建议显示使用,如cv::imshow
using namespace cv;
using namespace std;

//显示帮助信息
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;
}


//数据类
class MyData
{
public:
    MyData() : A(0), X(0), id()//构造函数
    {}
    explicit MyData(int) : A(97), X(CV_PI), id("mydata1234") // 显示构造函数，防止隐式调用
    {}
    void write(FileStorage& fs) const//顺序写类的数据函数，为常成员函数，不能修改数据。
    {
        fs << "{" << "A" << A << "X" << X << "id" << id << "}";
    }
    void read(const FileNode& node)//读取数据函数
    {
        A = (int)node["A"];
        X = (double)node["X"];
        id = (string)node["id"];
    }
public:   // Data Members
//数据成员
    int A;
    double X;
    string id;
};

//写数据函数，为静态函数，函数内调用类内成员函数
static void write(FileStorage& fs, const std::string&, const MyData& x)
{
    x.write(fs);
}
//读取数据函数，为静态函数，函数内调用类内成员函数
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
//重载<<运算符
static ostream& operator<<(ostream& out, const MyData& m)
{
    out << "{ id = " << m.id << ", ";
    out << "X = " << m.X << ", ";
    out << "A = " << m.A << "}";
    return out;
}

int main(int ac, char** av)
{
    //检查输入参数
    if (ac != 2)
    {
        help(av);
        return 1;
    }

    string filename = av[1];//文件路径名
    //把MyData类对象的数据写到文件里面
    { 
        Mat R = Mat_<uchar>::eye(3, 3),
            T = Mat_<double>::zeros(3, 1);
        MyData m(1);

        FileStorage fs(filename, FileStorage::WRITE);//以写的方式打开文件

        //按照一对一的键值对格式输出到文件
        fs << "iterationNr" << 100;
        //使用中括号输出序列到文件
        fs << "strings" << "[";                              // text - string sequence
        fs << "image1.jpg" << "Awesomeness" << "../data/baboon.jpg";
        fs << "]";                                           // close sequence

        //以花括号的格式输出数据到文件
        fs << "Mapping";                              // text - mapping
        fs << "{" << "One" << 1;
        fs <<        "Two" << 2 << "}";

        //输出矩阵
        fs << "R" << R;                                      // cv::Mat
        fs << "T" << T;
        fs << "MyData" << m;                                // your own data structures

        fs.release();                                       // explicit close
        cout << "Write Done." << endl;
    }

    {//read
    //打开文件读取数据到MyData类对象
        cout << endl << "Reading: " << endl;
        FileStorage fs;
        fs.open(filename, FileStorage::READ);//以读的方式打开文件

        int itNr;
        //fs["iterationNr"] >> itNr;

        //读取一对一的键值对数据
        itNr = (int) fs["iterationNr"];
        cout << itNr;
        //检查文件是否正常打开
        if (!fs.isOpened())
        {
            cerr << "Failed to open " << filename << endl;
            help(av);
            return 1;
        }

        //读取一对多的中括号序列格式数据
        FileNode n = fs["strings"];                         // Read string sequence - Get node
        if (n.type() != FileNode::SEQ)
        {
            cerr << "strings is not a sequence! FAIL" << endl;
            return 1;
        }
        //使用迭代器
        FileNodeIterator it = n.begin(), it_end = n.end(); // Go through the node
        for (; it != it_end; ++it)
            cout << (string)*it << endl;

        //读取花括号格式数据
        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;
        //读取矩阵数据
        fs["R"] >> R;                                      // Read cv::Mat
        fs["T"] >> T;
        //读取MyData类数据
        fs["MyData"] >> m;                                 // Read your own structure_

        cout << endl
            << "R = " << R << endl;
        cout << "T = " << T << endl << endl;
        cout << "MyData = " << endl << m << endl << endl;//重载的运算符这里被使用

        //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;
}

//FileStorage
XML/YAML/JSON file storage class that encapsulates all the information necessary for writing or reading data to/from a file.
//FileNode
File Storage Node class.

The node is used to store each and every element of the file storage opened for reading. When XML/YAML file is read, it is first parsed and stored in the memory as a hierarchical collection of nodes. Each node can be a "leaf" that is contain a single number or a string, or be a collection of other nodes. There can be named collections (mappings) where each element has a name and it is accessed by a name, and ordered collections (sequences) where elements do not have names but rather accessed by index. Type of the file node can be determined using FileNode::type method.

Note that file nodes are only used for navigating file storages opened for reading. When a file storage is opened for writing, no data is stored in memory after it is written.

//写数据函数，为静态函数，函数内调用类内成员函数
static void write(FileStorage& fs, const std::string&, const MyData& x)
{
    x.write(fs);
}
//读取数据函数，为静态函数，函数内调用类内成员函数
static void read(const FileNode& node, MyData& x, const MyData& default_value = MyData()){
    if(node.empty())
        x = default_value;
    else
        x.read(node);
}