Opencv对XML和YAML文件实现I/O操作

1. XML、YAML文件的打开和关闭
XML\YAML文件在OpenCV中的数据结构为FileStorage，打开操作例如：

string filename = "I.xml";  
FileStorage fs(filename,FileStorage::WRITE);  
\\...  
fs.open(filename,FileStorage::READ);

文件关闭操作会在FileStorage结构销毁时自动进行，但也可调用如下函数实现

fs.release();

2.文本和数字的输入和输出

写入文件使用 << 运算符，例如：

fs << "iterationNr" << 100;

读取文件，使用 >> 运算符，例如

int itNr;  
fs["iterationNr"] >> itNr;  
itNr = (int) fs["iterationNr"];

3. OpenCV数据结构的输入和输出，和基本的C++形式相同

Mat R = Mat_<uchar >::eye (3,3),T = Mat_<double>::zeros(3,1);  
fs << "R" << R; // Write cv::Mat  
fs << "T" << T;  
fs["R"] >> R; // Read cv::Mat  
fs["T"] >> T;

4. vector（arrays）和 maps的输入和输出
vector要注意在第一个元素前加上“[”，在最后一个元素前加上"]"。例如：

fs << "strings" << "["; // text - string sequence  
fs << "image1.jpg" << "Awesomeness" << "baboon.jpg";  
fs << "]"; // close sequence

对于map结构的操作使用的符号是"{"和"}"，例如：

fs << "Mapping"; // text - mapping  
fs << "{" << "One" << 1;  
fs << "Two" << 2 << "}";

读取这些结构的时候，会用到FileNode和FileNodeIterator数据结构。对FileStorage类的[]操作符会返回FileNode数据类型，对于一连串的node，可以使用FileNodeIterator结构，例如：

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;

5. 读写自己的数据结构
这部分比较复杂，参考最后的实例中的MyData结构自己领悟吧

最后，我这里上一个实例，供大家参考。

源文件里填入如下代码：

#include <opencv2/core/core.hpp>  
#include <iostream>  
#include <string>  
  
using namespace cv;  
using namespace std;  
  
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;  
}  
  
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  
void write(FileStorage& fs,const std::string&,const MyData& x)  
{  
    x.write(fs);  
}  
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  
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)  
{  
    if (ac != 2)  
    {  
        help(av);  
        return 1;  
    }  
  
    string filename = av[1];  
    { //write  
        Mat R = Mat_<uchar>::eye(3,1);  
        MyData m(1);  
  
        FileStorage fs(filename,FileStorage::WRITE);  
  
        fs << "iterationNr" << 100;  
        fs << "strings" << "[";                              // text - string sequence  
        fs << "image1.jpg" << "Awesomeness" << "baboon.jpg";  
        fs << "]";                                           // close sequence  
          
        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;  
        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;  
}

编译后，在命令行进入到文件目录，执行test test.xml，运行结果如下，生成一个test . xml文件，内容如下：

 <?xml version="1.0" ?>   
- <opencv_storage>  
  <iterationNr>100</iterationNr>   
  <strings>image1.jpg Awesomeness baboon.jpg</strings>   
- <Mapping>  
  <One>1</One>   
  <Two>2</Two>   
  </Mapping>  
- <R type_id="opencv-matrix">  
  <rows>3</rows>   
  <cols>3</cols>   
  <dt>u</dt>   
  <data>1 0 0 0 1 0 0 0 1</data>   
  </R>  
- <T type_id="opencv-matrix">  
  <rows>3</rows>   
  <cols>1</cols>   
  <dt>d</dt>   
  <data>0. 0. 0.</data>   
  </T>  
- <MyData>  
  <A>97</A>   
  <X>3.1415926535897931e+000</X>   
  <id>mydata1234</id>   
  </MyData>  
  </opencv_storage>

Opencv对XML和YAML文件实现I/O操作

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