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Subject: [Boost-users] Writing large binary files with boost gzip
From: Anders Knudby (knudby_at_[hidden])
Date: 2011-04-07 15:09:12

Hello all, please help! I'm truly banging my head against the wall here. I
am trying to write a function that will allow me to write gzipped binary
files (~50 MB) and read them again. I have data in memory. Here's my code
for writing:

    namespace io = boost::iostreams;

    filename = "c:/test.bin.gz"; //My output file
    int size = 5000000; //Data size in bytes, ~5 MB

    //Create filtering_ostream
    io::filtering_ostream out; //Creates a filtering_ostream called out
    out.push(io::gzip_compressor()); //Assigns the gzip_compressor to out
    out.push(io::file_sink(filename)); //Assigns a file sink to out

    char* memblock = new char [size]; //This is my data. In reality memblock
will have been created earlier and filled with real data

    out.write(memblock, size); //Do the writing

    delete[] memblock; //Clean up

As written above the resulting file, c:/test.bin.gz, is corrupt. If I try to
decompress it, either with gzip or winrar, I get an error message. However,
if I instead set size = 4000000 (~4 MB) (slightly smaller), the resulting
file works just fine. My problem therefore is that my actual size is 50

Please help!
Anders (not a real programmer)

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