Inflation of pdf stream using zlib blank sometimes - c++

Question

I am a beginner programmer trying to inflate text stream from pdfs. I have adopted and slightly altered some open source code which uses zlib, and generally it works very well. However, I have been testing on some different pdfs lately and some of the inflated streams are returning blank. Could anybody advise me as to why?
I have come across this question below which seems to address the same problem but does not really give a definitive answer
zLib inflate has empty result in some cases
#include <iostream>
#include <fstream>
#include <string>
#include "zlib.h"
int main()
{
//Discard existing output:
//Open the PDF source file:
std::ifstream filei("C:\\Users\\dpbowe\\Desktop\\PIDSearch\\P&ID.PDF", std::ios::in|std::ios::binary|std::ios::ate);
if (!filei) std::cout << "Error Opening Input File" << std::endl;
//decoded output
std::ofstream fileo;
fileo.open("C:\\Users\\dpbowe\\Desktop\\Decoded.txt", std::ios::binary | std::ofstream::out);
if (!fileother) std::cout << "Error opening output file" << std::endl;
if (filei && fileo)
{
//Get the file length:
long filelen = filei.tellg(); //fseek==0 if ok
filei.seekg(0, std::ios::beg);
//Read the entire file into memory (!):
char* buffer = new char [filelen];
if (buffer == NULL) {fputs("Memory error", stderr); exit(EXIT_FAILURE);}
filei.read(buffer,filelen);
if (buffer == '\0') {fputs("Reading error", stderr); exit(EXIT_FAILURE);}
bool morestreams = true;
//Now search the buffer repeated for streams of data
while (morestreams)
{
//Search for stream, endstream. Should check the filter of the object to make sure it if FlateDecode, but skip that for now!
size_t streamstart = FindStringInBuffer (buffer, "stream", filelen); //This is my own search function
size_t streamend = FindStringInBuffer (buffer, "endstream", filelen); //This is my own search function
if (streamstart>0 && streamend>streamstart)
{
//Skip to beginning and end of the data stream:
streamstart += 6;
if (buffer[streamstart]==0x0d && buffer[streamstart+1]==0x0a) streamstart+=2;
else if (buffer[streamstart]==0x0a) streamstart++;
if (buffer[streamend-2]==0x0d && buffer[streamend-1]==0x0a) streamend-=2;
else if (buffer[streamend-1]==0x0a) streamend--;
//Assume output will fit into 10 times input buffer:
size_t outsize = (streamend - streamstart)*10;
char* output = new char [outsize]; ZeroMemory(output, outsize);
//Now use zlib to inflate:
z_stream zstrm; ZeroMemory(&zstrm, sizeof(zstrm));
zstrm.avail_in = streamend - streamstart + 1;
zstrm.avail_out = outsize;
zstrm.next_in = (Bytef*)(buffer + streamstart);
zstrm.next_out = (Bytef*)output;
int rsti = inflateInit(&zstrm);
if (rsti == Z_OK)
{
int rst2 = inflate (&zstrm, Z_FINISH);
if (rst2 >= 0)
{
size_t totout = zstrm.total_out;
//Write inflated output to file "Decoded.txt"
fileother<<output;
fileother<<"\r\nStream End\r\n\r\n";
}
else std::cout<<"output uncompressed stream is blank"<<std::endl;
}
delete[] output; output=0;
buffer+= streamend + 7;
filelen = filelen - (streamend+7);
}
else
{
morestreams = false;
std::cout<<"End of File"<<std::endl;
}
}
filei.close();
}
else
{
std::cout << "File Could Not Be Accessed\n";
}
if (fileo) fileo.close();
}