Use the boost: iostreams library to compress and decompress data

Use the boost: iostreams library to compress and decompress data.-Bo Cheng's blog-blog channel-csdn. net

Use the boost: iostreams library to compress and decompress data Category: boost 92 people reading Comment (0) Favorites Report Boostboostiostreams

In today's project, we are going to use gzip to compress the data and find the boost: iostreams library. Therefore, we checked the relevant information. Below we will record some of our understanding about this library.

Iostreams consists of two main types: Device and filter, which can be found in the source code directory. The iostreams directory contains these two directories to find related classes.

Device is like a device,It cannot be used independently. It must be used with a normal stream or stream_buffer,You can input/output data in the stream to this device, which can be divided

Source, which accesses character sequences in Read mode, such as: file_source for file input.

Sink, which accesses character sequences in write mode, such as: file_sink for file output.

Stream <file_source> is a file input stream, similar to ifilestream, and stream <file_sink> is a file output stream, similar to ofilestream.

A filter is similar to a device and cannot be used independently. It must be used with a filter stream.Filtering_streamOrFiltering_streambufTo filter the data in the stream according to one rule, which can be divided:

inputfilter, filter the input read by source. example: gzip_deco Mpressor decompress the data in the stream by gzip algorithm .
outputfilter: filters the output written to the sink. for example: gzip_compressor compresses the data in the stream according to the gzip algorithm .

HoweverFiltering_stream maintains a filter linked list, ending with device. The output filter stream filtering_ostream is used to execute the filter in sequence and then output it to Devic, for example:

Compression time

Filtering_ostream out;
Out. Push (gzip_compressor ()); // Gzip outputfilter

Out. Push (bzip2_compressor (); // Bzip2 outputfilter
Out. Push (boost: iostreams: file_sink ("test.txt"); // end with file_sink Device

This will first compress the data to the GZIP file, and then compress the data to the text.txt file.

Decompress

Filtering_istream in;
In. Push (gzip_decompressor ();/gzip inputfilter

In. Push (gzip_compressor ();/Bzip2 inputfilter
In. Push (file_source ("test.txt "));

In this case, read the data in the test.txt file, decompress Bzip2, decompress gzip, and store the data in the in stream. This is exactly the reverse compression order.

ImplementationCode

# Include <boost/iostreams/filtering_stream.hpp>
# Include <boost/iostreams/device/file_descriptor.hpp>
# Include <boost/iostreams/device/file. HPP>
# Include <iostream>
# Include <sstream>
Int main ()
{
  Try {
  STD: String DEST;
Boost: iostreams: filtering_ostream out;
Out. Push (boost: iostreams: gzip_compressor ());
// Out. Push (boost: iostreams: file_sink ("test.txt "));
Out. Push (boost: iostreams: back_inserter (DEST ));
// Boost: iostreams: Write (Out, "hello", 5 );
Boost: iostreams: Copy (STD: stringstream ("hello"), OUT );
STD: cout <"DEST:" <DEST <STD: Endl;
Boost: iostreams: filtering_istream in;
In. Push (boost: iostreams: gzip_decompressor ());
// In. Push (boost: iostreams: file_source ("test.txt "));
STD: stringstream SS (DEST );
In. Push (SS );
Char text [100] = {0 };
Boost: iostreams: Read (in, text, 4 );
// Boost: iostreams: Copy (in, STD: stringstream (text ));
STD: cout <"text:" <text <STD: Endl;
}
Catch (STD: exception & E)
{
STD: cout <"exception:" <E. What () <STD: Endl;
}
Catch (...)
{
STD: cout <"unknown exception." <STD: Endl;
}
System ("pause ");
Return 0;
}