How do i write multiple streams to an XML file using OpenCV XML/YAML persistence?

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C++

XML

OpenCV

Hi i tried to write multiple objects to a single XML file using openCV XML/YAML persistence. See example code below.

#include "opencv2/opencv.hpp"

using namespace cv;

struct User_point
{
	int x,y;
};

void WritePoint(User_point& pnt,CvFileStorage* fs)
	{
		cvStartWriteStruct(fs,"User_point",CV_NODE_SEQ);
		  cvWriteInt(fs,0,pnt.x);
		  cvWriteInt(fs,0,pnt.y);
		cvEndWriteStruct(fs);
	}

void main() 
{

	User_point point;

	point.x = 20;
	point.y = 20;
	CvFileStorage* fs = cvOpenFileStorage("user.xml",0,CV_STORAGE_WRITE);
		if(fs)
		{
			WritePoint(point,fs);
			point.x=10;
			point.y = 10;
			cvStartNextStream(fs);
			WritePoint(point,fs);
		}


	    cvReleaseFileStorage( &fs );
  return;
}

The resulting xml file looks like this

<?xml version="1.0"?>
<opencv_storage>
<User_point>
  20 20</User_point>

<!-- next stream -->
<User_point>
  10 10</User_point>
</opencv_storage>

The problem occurs when openCV tries to parse the file when opening it. The code for reading the xml file is shown below.

#include "opencv2/opencv.hpp"
#include "iostream"

using namespace cv;

using namespace std;

struct User_point
{
	int x,y;
};

bool ReadPoint(User_point& pnt,CvFileStorage* fs,CvFileNode* fn=0)
	{
	   CvFileNode* fn2 = cvGetFileNodeByName(fs,fn,"User_point");
	   if(fn2)
	   {
		pnt.x = cvReadInt((CvFileNode*)cvGetSeqElem(fn2->data.seq,0));
		pnt.y = cvReadInt((CvFileNode*)cvGetSeqElem(fn2->data.seq,1));
	   }
	   else
	      return false;
	   return true;
	}

void main() 
{

	User_point point;

	CvFileStorage* fs = cvOpenFileStorage("user.xml",0,CV_STORAGE_READ);
	    CvFileNode* fn = cvGetRootFileNode(fs,0);
		if(fn)
		{
			ReadPoint(point,fs,fn);
			cout<<point.x<<":"<<point.y<<"\n";
		}
		fn = cvGetRootFileNode(fs,1);
		if(fn)
		{
			ReadPoint(point,fs,fn);
			cout<<point.x<<":"<<point.y<<"\n";
		}
		cvReleaseFileStorage( &fs );
  return;
}

The openCV reports an error "Duplicate Key" during parsing. My question is how do i write multiple user defined objects to an xml file using openCV without such an error popping up? I tried nesting them but nesting is limited to a certain number.

Would appreciate any contribution.