Categories: Symbian C++ | Code Examples | Files/Data | S60 3rd Edition, Feature Pack 1

This page was last modified 11:26, 14 May 2008.

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Overview

This snippet shows how to compress and decompress GZIP files using classes CEZFileToGZip and CEZGZipToFile.

This snippet can be self-signed.

MMP file

The following libraries are required:

LIBRARY efsrv.lib
LIBRARY ezlib.lib

Header file

Source file

#include <ezgzip.h>
#include <f32file.h>
 
void CompressGZipFileL(RFs &aFs, TInt aBufferSize, const TDesC& aFileName)
{
   RFile input;
 
   HBufC *compressedFile = HBufC::NewLC(aFileName.Length()+3);
  _LIT(KCompressedGZipFileName,"%S.gz");
  compressedFile->Des().Format(KCompressedGZipFileName,&aFileName);
      
  User::LeaveIfError(input.Open(aFs,aFileName,EFileStream | EFileRead | EFileShareAny));
  CleanupClosePushL(input);
 
  CEZFileToGZip *fileToGZip = CEZFileToGZip::NewLC(aFs,*compressedFile,input,aBufferSize);
      
  _LIT(KCompressingToGZipFile,"Compressing file %S to gzip file %S\n");
  console->Printf(KCompressingToGZipFile,&aFileName,compressedFile);
      
  while (fileToGZip->DeflateL())
    {
    // loop here until the gzip file is created
    }
    
  CleanupStack::PopAndDestroy(3); //fileToGZip, input, compressedFile
}
 
void DecompressGZipFileL(RFs &aFs, TInt aBufferSize, const TDesC& aFileName)
{
  TInt err(KErrNone);
  RFile output;
      
  HBufC *decompressedFile = HBufC::NewLC(aFileName.Length()+1);
  _LIT(KDecompressedGZipFileName,"%S_");
  decompressedFile->Des().Format(KDecompressedGZipFileName,&aFileName);
      
  err = output.Create(aFs, *decompressedFile,EFileStream | EFileWrite |
 EFileShareExclusive);
  if (err == KErrAlreadyExists)
    User::LeaveIfError(output.Open(aFs, *decompressedFile,EFileStream |
 EFileWrite | EFileShareExclusive));
  else 
    User::LeaveIfError(err);
  CleanupClosePushL(output);
      
  CEZGZipToFile *gZipToFile = CEZGZipToFile::NewLC(aFs,aFileName,output,aBufferSize);
      
  _LIT(KDecompressingFromGZipFile,"Decompressing file %S from gzip file %S\n");
  console->Printf(KDecompressingFromGZipFile, decompressedFile, &aFileName);
      
  while (gZipToFile->InflateL())
    {
    // loop here until the gzip file is decompressed
    }
 
    CleanupStack::PopAndDestroy(3); //gZipToFile, output, decompressedFile
}

Using CompressGZipFileL() and DecompressGZipFileL() methods

This simple example method reads command line arguments and compresses or decompresses .gz files.

options:

• -c = compress
• -d = decompress
• -b n = buffer size
• filename = gzip file

void doGZipCompressionAndDecompressionL()
  {
  RFs fs;
  User::LeaveIfError(fs.Connect());
  CleanupClosePushL(fs);
  
  TBool doCompress = ETrue;
  TInt bufferSize = 32768;
  TInt cmdLineLen = User::CommandLineLength();
    
  if (cmdLineLen <= 0)
    {
    _LIT(KUsage,"Usage: program.exe [-cd] [-u buffer] filename\n");
    console->Printf(KUsage);
    User::Leave(KErrGeneral);
    }
 
  HBufC *argv = HBufC::NewLC(cmdLineLen);
  TPtr argPtr=argv->Des();
  User::CommandLine(argPtr);
 
  TLex arguments(*argv);
 
  TPtrC options(arguments.NextToken());
  TBool bufferSizeSpecified = EFalse;
  
  _LIT(KInvalidOption,"Invalid option %S\n");
  _LIT(KUnknownOption,"Unknown option %S\n");
  _LIT(KNoOptionSpecified,"No option specified\n");
  
  while (options[0]=='-' || bufferSizeSpecified)
    {
    TInt index = 1;
 
    if (bufferSizeSpecified)
      {
      if (options.Length() == 0)
        {
        console->Printf(KNoOptionSpecified);
        console->Getch();
        User::Leave(KErrGeneral);
        }
      else
        {
        TLex lex(options);
        TInt ret(KErrNone);         
        
       	ret = lex.Val(bufferSize);
       	bufferSizeSpecified = EFalse;
        
        if (ret != KErrNone)
          {
          console->Printf(KInvalidOption,&options);
          console->Getch();
          User::Leave(KErrGeneral);
          }
        }
      }
    else
      {        
      while (index < options.Length())
        {
        if (options[index] == 'd')
          doCompress = EFalse;
        else if (options[index] == 'c')
          doCompress = ETrue;
        else if (options[index] == 'b' )
       	  bufferSizeSpecified = ETrue;	
        else 
          {
          console->Printf(KUnknownOption,&options);
          console->Getch();
          User::Leave(KErrGeneral);
          }
        index++;
        }
      
      if (index == 1)
        {        
        console->Printf(KNoOptionSpecified);
        console->Getch();
        User::Leave(KErrGeneral);
        }
      }
    options.Set(arguments.NextToken());
    }
    
    TPtrC fileNamePtr(options);
    HBufC *fileNameBuf = HBufC::NewLC(fileNamePtr.Length());
    *fileNameBuf = fileNamePtr;
            
    if(doCompress)
   	CompressGZipFileL(fs,bufferSize,*fileNameBuf);
    else
   	DecompressGZipFileL(fs,bufferSize,*fileNameBuf);
 
    CleanupStack::PopAndDestroy(3); //fileNameBuf,argv,fs
  }

Postconditions

Depending on given parameters and the used method, GZIP files are compressed or decompressed.

See also

CS000948 - Getting trailer and header info from GZIP files

The gzip format is specified in the page http://www.faqs.org/rfcs/rfc1952.html.