C++: Iterating lines in a GZ file using boost::iostreams
Problem:
You’ve got a gzipped file that you want to decompress using C++. You don’t want to use pipes to gzip in an external process. You don’t want to use zlib and manual buffering either.
Solution:
This is an extension of the official gzip_decompressor example. It is also applicable to bzip2 files, assuming you use the correct decompressor filter.
The program takes a single command line argument (which is a gzipped file) and prints its decompressed output to stdout.
/**
* myzcat.cpp
* A zcat replacement, for educational purpose.
* Uses boost::iostream and zlib.
*
* Compile like this:
* clang++ -o myzcat myzcat.cpp -lz -lboost_iostreams
*
* This code is published as public domain.
*/
#include <fstream>
#include <iostream>
#include <boost/iostreams/filtering_streambuf.hpp>
#include <boost/iostreams/copy.hpp>
#include <boost/iostreams/filter/gzip.hpp>
int main(int argc, char** argv) {
if(argc < 2) {
std::cerr << "Usage: " << argv[0] << " <gzipped input file>" << std::endl;
}
//Read from the first command line argument, assume it's gzipped
std::ifstream file(argv[1], std::ios_base::in | std::ios_base::binary);
boost::iostreams::filtering_streambuf<boost::iostreams::input> inbuf;
inbuf.push(boost::iostreams::gzip_decompressor());
inbuf.push(file);
//Convert streambuf to istream
std::istream instream(&inbuf);
//Iterate lines
std::string line;
while(std::getline(instream, line)) {
std::cout << line << std::endl;
}
//Cleanup
file.close();
}