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Zlib Compression

Posted on 2004-04-02
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Last Modified: 2011-04-14
Hi,

Can someone help me with the following code. Basically my requirement is to create an archive (a zip file) with serveral files.

The following code opens the "testxml2.txt" file and tries to write it to the Test.Zip file. Test.zip file is getting created with 1KB but "write" operation is not working.


#define _WINDOWS
#define ZLIB_DLL

#include "zlib.h"
#include <fstream>
#include <iostream>

using namespace std;

int CompressFile(char type, char *filename, long startFilePos, char *outfilename, char fileAction);

enum {COMPRESS,UNCOMPRESS, NEWFILE, APPENDFILE};

int main(int argc, char *argv[])
{
      
      int error;

      error=CompressFile(COMPRESS, "c:\\testxml2.txt", 0, "Test.zip", NEWFILE);

      cout << "Error  " << error << endl;

      return 0;
}

int CompressFile(char type, char *filename, long startFilePos, char *outfilename, char fileAction)
{
      z_stream stream;
      int err;
      int level;
      ifstream inFile;
      ofstream outFile;
      bool done=false, atEOF=false;
      unsigned char *incData=NULL, *outData=NULL;
      int inSize, outSize, count;
      int BUFFER_SIZE=3000;

      level=3;
    stream.zalloc = Z_NULL;
    stream.zfree  = Z_NULL;
    stream.opaque = Z_NULL;

      // Initalize ZLIB
      if (type==COMPRESS)
            err = deflateInit(&stream, level);
      else
            err = inflateInit(&stream);

    if (err != Z_OK) return err;

      inSize=BUFFER_SIZE;
      outSize=inSize*(float)1.001+14;
      
      if ((incData=new unsigned char[inSize])==NULL)
      {err=Z_MEM_ERROR; goto cleanup;}
      
      if ((outData=new unsigned char[outSize])==NULL)
      {err=Z_MEM_ERROR; goto cleanup;}

      inFile.open(filename, ios::in);
      if (!inFile)
            goto cleanup;

      if (fileAction==NEWFILE)
            outFile.open(outfilename, ios::in | ios::app);
      else
            outFile.open(outfilename);
      if (!outFile)
            goto cleanup;

      if (startFilePos>0)
            inFile.seekg(startFilePos,ios::beg);
      
      stream.avail_in=0;
      stream.next_in=incData;
      stream.avail_out=outSize;
      stream.next_out=outData;
      //do
      //{
       while (stream.avail_in==0 && stream.avail_out==outSize && atEOF==false)
       {

            if (stream.avail_in==0)
            {
                  inFile.read((char *)incData,inSize);
                  cout << incData << endl;
                  stream.next_in=incData;
                  stream.avail_in=inFile.gcount();
                  atEOF=inFile.eof();
            }
              

            // Do some compressing
            if (type==COMPRESS)
                  err = deflate(&stream, Z_NO_FLUSH);
            else
                  err = inflate(&stream, Z_NO_FLUSH);

      
            if (err != Z_OK)
                  goto cleanup;
            
                  count=outSize-stream.avail_out;
                  if (count)
                     outFile.write((char *)outData,count);
                  stream.next_out=outData;
                  stream.avail_out=outSize;

}      

cleanup:

      inFile.close();
      outFile.close();

      if (err!=Z_OK)
            unlink(outfilename);

      if (type==COMPRESS)
            deflateEnd(&stream);
      else
            inflateEnd(&stream);
      
      if (incData!=NULL) delete incData;
      if (outData!=NULL) delete outData;

      return err;
}

Thanks.
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Question by:newuser11
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5 Comments
 
LVL 44

Expert Comment

by:Karl Heinz Kremer
ID: 10745250
Your problem is here;

    if (fileAction==NEWFILE)
          outFile.open(outfilename, ios::in | ios::app);

You are opening an ofstream with ios::in. This will not work. Change ios::in to ios::out, and you should be able to run your program (it works at least if I run it under Linux - I don't have zlib for Windows installed).
0
 

Author Comment

by:newuser11
ID: 10758409
Hi khkremer,

When you said you were able to run it. Did it create a .zip file with the contents. For me it creates the zip file and it says it's not a valid archive file. When I try to uncompress it the file got created with 0 bytes.

Thanks.
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LVL 44

Accepted Solution

by:
Karl Heinz Kremer earned 250 total points
ID: 10762539
You are right, it's not a valid archive file Are you aware of the example.c file in the zlib distribution? It does contain samples for using the different functions.

You should probably not mix compression and decompression in the same function, this can get pretty confusing. Look at example.c and try to remplement this in your own code.
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