examples/containers/copy_file.cpp

This is an example of how to copy a file to another using STXXL's asynchronous I/O features.

/***************************************************************************
 * examples/containers/copy_file.cpp
 *
 * This example shows three methods to copy a file to another file using
 * stxxl:vectors.
 *
 * Part of the STXXL. See http://stxxl.sourceforge.net
 *
 * Copyright (C) 2004-2006 Roman Dementiev <[email protected]>
 * Copyright (C) 2013 Timo Bingmann <[email protected]>
 *
 * Distributed under the Boost Software License, Version 1.0.
 * (See accompanying file LICENSE_1_0.txt or copy at
 * http://www.boost.org/LICENSE_1_0.txt)
 **************************************************************************/

#include <stxxl/io>
#include <stxxl/vector>
#include <stxxl/stream>

void copy_file(const char* input_path, const char* output_path, unsigned int method)
{
 using stxxl::file;

 file::unlink(output_path); // delete output file

 stxxl::timer tm(true); // start a timer

 // input file object
 stxxl::syscall_file InputFile(input_path, file::RDONLY | file::DIRECT);
 // output file object
 stxxl::syscall_file OutputFile(output_path, file::RDWR | file::CREAT | file::DIRECT);

 typedef stxxl::vector<unsigned char> vector_type;

 std::cout << "Copying file " << input_path << " to " << output_path << std::endl;

 // InputVector is mapped to InputFile
 vector_type InputVector(&InputFile);
 vector_type OutputVector(&OutputFile); // OutputVector is mapped to OutputFile

 std::cout << "File " << input_path << " has size " << InputVector.size() << " bytes." << std::endl;

 if (method == 1)
 {
 // First method: copy vector elements. This is rather slow, because no
 // prefetching is used and the vector's pager does lots of internal
 // work!

 std::cout << "Using first method: copying vector elements." << std::endl;

 for (vector_type::const_iterator it = InputVector.begin(); // iterate through InputVector
 it != InputVector.end(); ++it)
 {
 OutputVector.push_back(*it); // add the value pointed by 'it' to OutputVector
 }
 }
 else if (method == 2)
 {
 // Second method: use a vector_iterator2stream to prefetch blocks in
 // the input vector and a vector_bufwriter for buffered writing to the
 // output.

 std::cout << "Using second method: vector_iterator2stream and vector_bufwriter." << std::endl;

 // prepare output vector's size
 OutputVector.resize(InputVector.size());

 // construct prefetching input stream
 stxxl::stream::vector_iterator2stream<vector_type::const_iterator>
 input(InputVector.begin(), InputVector.end());

 // construct buffered output writer
 vector_type::bufwriter_type writer(OutputVector.begin());

 while (!input.empty()) // iterate through InputVector
 {
 writer << *input;
 ++input;
 }
 writer.finish(); // flush buffers
 }
 else if (method == 3)
 {
 // Third method: use a vector_iterator2stream to prefetch blocks in the
 // input vector and materialize to write the stream to the output.

 std::cout << "Using third method: vector_iterator2stream and materialize." << std::endl;

 // prepare output vector's size
 OutputVector.resize(InputVector.size());

 // construct prefetching input stream
 stxxl::stream::vector_iterator2stream<vector_type::const_iterator>
 input(InputVector.begin(), InputVector.end());

 // materilize intput directly into output vector
 stxxl::stream::materialize(input, OutputVector.begin(), OutputVector.end());
 }

 std::cout << "Copied in " << tm.seconds() << " at "
 << (double)InputVector.size() / tm.seconds() / 1024 / 1024 << " MiB/s" << std::endl;
}

int main(int argc, char* argv[])
{
 if (argc < 3)
 {
 std::cout << "Usage: " << argv[0] << " input_file output_file [method 1-3]" << std::endl;
 return -1;
 }

 int method = (argc >= 4) ? atoi(argv[3]) : 3;

 copy_file(argv[1], argv[2], method);

 return 0;
}