Pb with zlib file limit at 8ko

test_gzlib_g++.cpp

// g++ -o test_gzlib_g++ test_gzlib.cpp `pkg-config --cflags --libs zlib`

#include <iostream>
#include <cstring>
#include <zlib.h>

const char data[] = "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse elementum varius lectus, quis tempor odio sodales eu. Nullam iaculis ante accumsan tortor molestie lacinia. Proin fringilla egestas enim id condimentum. Proin finibus vel neque eu posuere. Maecenas aliquet congue consectetur. Aenean dignissim, nisi id volutpat mollis, purus libero consectetur lorem, vitae bibendum orci eros id tortor. Proin efficitur enim leo, auctor commodo tortor gravida sit amet. Integer sit amet suscipit magna. Cras vel orci dolor. Nullam non ante ut magna mollis pretium. Aenean non ligula sapien. Etiam massa est, tristique vitae pharetra nec, interdum vitae turpis. Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Aliquam ut justo sit amet lacus pharetra hendrerit.";

int main(int argc, char *argv[])
{
  std::cout << "Data[" << strlen(data) << "]=" << data <<  std::endl;
  
  // open file
  gzFile fp = gzopen( "gz_output.gz", "w" );
  if( fp == nullptr ) {
    std::cerr << "Error opening gz_output.gz in writing" << std::endl;
    exit(1);
  }

  // write data
  for( unsigned int i = 0; i < 2000; ++i) {
    int nb_written = gzwrite( fp, data, strlen(data) );
    if( nb_written != strlen(data) ) {
      std::cerr << "Error writing nb_written=" << nb_written << " != " << strlen(data) << std::endl;
    }
  }  

  //close
  gzclose( fp );
      
  return 0;
}

On my Xubuntu 18.04, the size limit of file created using gzlib is 8ko... Why ?