User:Timothee Flutre/Notebook/Postdoc/2012/09/12: Difference between revisions
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* As usual, I'm not the only one who came up with something like this, have a look at [http://nilshomer.com/index.php?title=AFLIB AFLIB] by Niels Homer, a minimal C library integrating stdio, ZLIB and LIBBZIP2. | |||
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Handling compressed files with gzip in C++
Disclaimer: I am not a professional programmer, so I'm sure it's possible to do better (please, provide feedback!), but at least it's working smoothly for me and it should help other people as well. // Author: Timothee Flutre
// Aim: show how to use Zlib in your own C++ code
// Compilation: g++ -Wall -Wextra -g test.cpp -lz
// Not copyrighted -- provided to the public domain
#include <cmath>
#include <ctime>
#include <getopt.h>
#include <cerrno>
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
#include "zlib.h"
//-----------------------------------------------------------------------------
// copy-paste and use the four following functions in your own code
void
openFile (
const string & pathToFile,
gzFile & fileStream,
const char * mode)
{
fileStream = gzopen (pathToFile.c_str(), mode);
if (fileStream == NULL)
{
cerr << "ERROR: can't open file " << pathToFile
<< " with mode " << *mode
<< " (errno=" << errno << ")" << endl;
exit (1);
}
}
void
closeFile (
const string & pathToFile,
gzFile & fileStream)
{
int ret = gzclose (fileStream);
if (ret != Z_OK)
{
cerr << "ERROR: can't close the file " << pathToFile
<< ", gzclose() returned " << ret << endl;
exit (1);
}
}
int
getline (
gzFile & fileStream,
string & line)
{
int res = 1, c;
line.clear ();
while (true)
{
c = gzgetc (fileStream);
if (c == -1) // eof or error
{
res = 0;
break;
}
else if (c == 10) // 10 is ASCII code for '\n'
break;
else
line.push_back (c);
}
return res;
}
void
gzwriteLine (
gzFile & fileStream,
const string & line,
const string & pathToFile,
const size_t & lineId)
{
// if (gzprintf (fileStream, "%s", line.c_str()) <= 0)
if (gzputs (fileStream, line.c_str()) < 0)
{
cerr << "ERROR: can't write line " << lineId
<< " in file " << pathToFile << endl;
exit (1);
}
}
//-----------------------------------------------------------------------------
// functions to show how it works
void
readAGzipFileWithZlib ()
{
cout << __FUNCTION__ << endl;
// create a dummy file via a system call
system ("rm -f data.txt.gz; echo -e \"aaa\nbb\nccc\" | gzip > data.txt.gz");
// read the dummy file using zlib API
string fileName = "data.txt.gz";
gzFile fileStream;
openFile (fileName, fileStream, "rb"); // works also if file not compressed
string line;
size_t lineId = 0;
while (getline (fileStream, line))
{
++lineId;
cout << "line " << lineId << ": " << line << endl;
}
if (! gzeof (fileStream))
{
cerr << "ERROR: can't read successfully file "
<< fileName << " up to the end" << endl;
exit (1);
}
closeFile (fileName, fileStream);
//clean
system ("rm -f data.txt.gz");
}
void writeAGzipFileWithZlib ()
{
cout << __FUNCTION__ << endl;
// write a dummy file using zlib API
string fileName = "data.txt.gz";
gzFile fileStream;
openFile (fileName, fileStream, "wb");
stringstream ssLine;
ssLine << "1";
for (size_t i = 1; i < 10; ++i)
ssLine << " " << (i+1);
ssLine << endl;
gzwriteLine (fileStream, ssLine.str(), fileName, 1);
closeFile (fileName, fileStream);
// read it via a system call
system ("zcat data.txt.gz");
// clean
system ("rm -f data.txt.gz");
}
int main (void)
{
readAGzipFileWithZlib ();
writeAGzipFileWithZlib ();
return EXIT_SUCCESS;
}
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