学习OpenCV范例（九）——输入输出XML和YAML文件

在OpenCV的学习中，经常会用到文件的输入输出，特别是XML和YAML格式的输出文件，如果大家有做过人脸识别就可以体会到，用主分量分析法得到的特征脸、平均脸等等数据都会被保存成为XML格式，方便下次使用时调用，OpenCV2版本比OpenCV1版本省去了很多函数，大家通过OpenCV中文网就可以查到，而且OpenCV2版本的输入输出使用与STL相同的 <</>> 输入/输出操作符，实现起来非常简单，在学习的过程中要特别注意，输入输出是map数据结构还是sequence数据结构，这两种结构上的操作会有所不同，现在我们就看看范例吧。

1、代码实现

#include "stdafx.h"


#include <opencv2/core/core.hpp>
#include <iostream>
#include <string>

using namespace cv;
using namespace std;

static void help()
{
	cout << endl
		<<" shows the usage of the OpenCV serialization functionality."         << endl
		<< "usage: "                                                                      << endl
		<<  " 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
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
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)
{

	string filename = "F:\\OpenCV2.4.8\\file_input_output\\file_input_output\\input_output.xml";
	{ //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;
		fs << "strings" << "[";                              // text - string sequence
		fs << "image1.jpg" << "Awesomeness" << "baboon.jpg";
		fs << "]";