Append a line of text to a gzip-compressed text file.

boostgz.cc

/*
Compile on Fedora 16 Linux:
g++ -O2 -Wall -g -o boostgz boostgz.cc -lboost_iostreams-mt
  */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fstream>
#include <iostream>
#include <boost/iostreams/filtering_streambuf.hpp>
#include <boost/iostreams/copy.hpp>
#include <boost/iostreams/filter/gzip.hpp>

using namespace std;

static int read_file(std::string& buf, const char *fn)
{
        ifstream file(fn, ios_base::in | ios_base::binary);
        boost::iostreams::filtering_streambuf<boost::iostreams::input> in;
        in.push(boost::iostreams::gzip_decompressor());
        in.push(file);

        std::istream inf(&in);

        while (inf.good()) {
                char tmpbuf[8192];

                inf.read(tmpbuf, sizeof(tmpbuf));
                buf.append(tmpbuf, inf.gcount());
        }

        return 0;
}

static void add_data(std::string& buf, const char *data)
{
        buf += data;
        buf += "\n";
}

static void write_file(std::string& buf, const char *fn)
{
        ofstream file(fn, ios_base::out | ios_base::binary | ios_base::trunc);
        boost::iostreams::filtering_streambuf<boost::iostreams::output> out;
        out.push(boost::iostreams::gzip_compressor());
        out.push(file);

        std::ostream outf(&out);

        outf.write(buf.c_str(), buf.size());
}

int main(int argc, char *argv[]) 
{
        if (argc != 3) {
                fprintf(stderr, "usage: %s [string to add] [file.gz]\n",
                        argv[0]);
                return 1;
        }

        const char *data = argv[1];
        const char *fn = argv[2];

        std::string buf;

        read_file(buf, fn);
        add_data(buf, data);
        write_file(buf, fn);

        return 0;
}