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POUsing boost::iostreams mapped_file_source and filtering_streambuf to decompress file
 

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  1. POUsing boost::iostreams mapped_file_source and filtering_streambuf to decompress file
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    <p>I plan to process large compressed files and I would like to memory map the files to speedup reading. I adopted the existing example with regular file input but cannot get it either compile nor work :-) I'm using C++ Boost 1.49</p> <p>Any suggestion welcome!</p> <pre><code>#include&lt;iostream&gt; #include&lt;boost/iostreams/filtering_streambuf.hpp&gt; #include&lt;boost/iostreams/copy.hpp&gt; #include&lt;boost/iostreams/filter/zlib.hpp&gt; #include&lt;boost/iostreams/device/file.hpp&gt; #include&lt;boost/iostreams/device/mapped_file.hpp&gt; void test_decoder_mmf() { using namespace std; using namespace boost::iostreams; //ifstream file("my_file.txt", ios_base::in | ios_base::binary); mapped_file_source file( "my_file.txt" ); filtering_streambuf&lt; input &gt; in; in.push(zlib_decompressor()); in.push(file); copy(in,cout); } int main() { test_decoder_mmf(); return 0; } In file included from /usr/local/include/boost/iostreams/operations.hpp:20:0, from /usr/local/include/boost/iostreams/detail/adapter/mode_adapter.hpp:24, from /usr/local/include/boost/iostreams/detail/resolve.hpp:19, from /usr/local/include/boost/iostreams/detail/push.hpp:24, from /usr/local/include/boost/iostreams/chain.hpp:29, from /usr/local/include/boost/iostreams/filtering_streambuf.hpp:17, from test_boost_iostreams2.cc:2: /usr/local/include/boost/iostreams/optimal_buffer_size.hpp: In function ‘std::streamsize boost::iostreams::optimal_buffer_size(const T&amp;) [with T = boost::iostreams::mapped_file_source, std::streamsize = long int]’: /usr/local/include/boost/iostreams/chain.hpp:248:9: instantiated from ‘void boost::iostreams::detail::chain_base&lt;Self, Ch, Tr, Alloc, Mode&gt;::push_impl(const T&amp;, std::streamsize, std::streamsize) [with T = boost::iostreams::mapped_file_source, Self = boost::iostreams::chain&lt;boost::iostreams::input, char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt; &gt;, Ch = char, Tr = std::char_traits&lt;char&gt;, Alloc = std::allocator&lt;char&gt;, Mode = boost::iostreams::input, std::streamsize = long int]’ /usr/local/include/boost/iostreams/chain.hpp:216:1: instantiated from ‘void boost::iostreams::detail::chain_base&lt;Self, Ch, Tr, Alloc, Mode&gt;::push(const T&amp;, std::streamsize, std::streamsize, typename boost::disable_if&lt;boost::iostreams::is_std_io&lt;T&gt; &gt;::type*) [with T = boost::iostreams::mapped_file_source, Self = boost::iostreams::chain&lt;boost::iostreams::input, char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt; &gt;, Ch = char, Tr = std::char_traits&lt;char&gt;, Alloc = std::allocator&lt;char&gt;, Mode = boost::iostreams::input, std::streamsize = long int, typename boost::disable_if&lt;boost::iostreams::is_std_io&lt;T&gt; &gt;::type = void]’ /usr/local/include/boost/iostreams/chain.hpp:500:7: instantiated from ‘void boost::iostreams::detail::chain_client&lt;Chain&gt;::push_impl(const T&amp;, std::streamsize, std::streamsize) [with T = boost::iostreams::mapped_file_source, Chain = boost::iostreams::chain&lt;boost::iostreams::input, char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt; &gt;, std::streamsize = long int]’ /usr/local/include/boost/iostreams/chain.hpp:488:1: instantiated from ‘void boost::iostreams::detail::chain_client&lt;Chain&gt;::push(const T&amp;, std::streamsize, std::streamsize, typename boost::disable_if&lt;boost::iostreams::is_std_io&lt;T&gt; &gt;::type*) [with T = boost::iostreams::mapped_file_source, Chain = boost::iostreams::chain&lt;boost::iostreams::input, char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt; &gt;, std::streamsize = long int, typename boost::disable_if&lt;boost::iostreams::is_std_io&lt;T&gt; &gt;::type = void]’ test_boost_iostreams2.cc:17:17: instantiated from here /usr/local/include/boost/iostreams/optimal_buffer_size.hpp:39:55: error: ‘optimal_buffer_size’ is not a member of ‘impl {aka boost::iostreams::detail::optimal_buffer_size_impl&lt;boost::iostreams::mapped_file_source&gt;}’ </code></pre>
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    1. COIf it won't compile, it's not likely to work. What is the compilation error for the code above?
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      1. USSteve Townsend
    2. CO@Steve Townsend - Steve thanks for responding. I tried several variants of the code and published the version which I thought was closest to how I would expect the code to be implemented (event hough it did not compile). I tried the code below but it ended up with exception: `mapped_file_source mmf( "my_file.txt" ); ifstream file; file.rdbuf()->pubsetbuf((char*)mmf.data(),mmf.size());`
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      1. USG. Civardi
 

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