How to find the index in Poco::DeflatingOutputStream - c++

Question

Hi I am new to usage of Poco , can you please help me to find a way to get the index/position during the writing into deflating stream so that I can truncate the invalid data and make sure my file contains only valid data.
#include <stdexcept>
#include <stdarg.h>
#include <map>
#include <iostream>
#include <cstring>
#include <fstream>
#include <Poco/DeflatingStream.h>
#include <stdio.h>
#include <limits>
#include <stdio.h>
#include <unistd.h>
using namespace std;
std::ofstream* ostr;
Poco::DeflatingOutputStream* ofstr;
string fileName="/home/lamb/Cpp/simple.gzip";
bool written = false;
// int lastsucessfulwrite;
compress(){
*ofstr << "\t<xyz>\n";
*ofstr << "\t</xyz>\n";
*ofstr << " who=\"";
*ofstr << "/>\n";
written = true;
/* "lastsucessfulwrite" How to store the index of ofstr , in case of normal files we use ftell but in DeflatingOutputStream how to get index so that I can erase it later based on this value */
}
timer(){
sleep(2);
// 2 second
written = false ;
}
close(){
ofstr->close();
delete ofstr;
ofstr = NULL;
ostr->close();
delete ostr;
ostr = NULL;
}
int main(){
ostr = new std::ofstream;
ostr->exceptions(std::ofstream::failbit|std::ofstream::badbit);
ostr->open(_fileName.c_str(), std::ios::binary | std::ios::app);
ofstr = new Poco::DeflatingOutputStream(*_ostr,
Poco::DeflatingStreamBuf::STREAM_GZIP);
ofstr->precision(std::numeric_limits<double>::digits10);
string data1 = "hello';
string data2 = "hello';
string data3 = "hello';
written = false ;
timer()//start
compress(data1);
if(written)
{
compress(data2);
}
if(written)
{
compress(data2);
}
if(written)
{
compress(data3);// timeup and time() is inovked and part of compress() is executed
}
// Now I would like to use lastsucessfulwrite as the key and truncate the paritally witten data3
// In case of normal file we use "truncate" system call
close();
}

Answer 1

You can use any standard C++ stream functions with Poco streams.
streampos pos = ofstr->tellp()