Serializing CStringList in the registry

Thursday Aug 6th 1998 by Mario Contestabile
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Serializing CStringList in the registry

The registry is an ideal place to store information about your application. Using a key and a Value Name you can easily store and retrieve Value Data once you get a hang of the registry APIs.

I recently encountered a scenario where I needed to store a list of strings in the registry. Typically, that would involve ::RegOpenKeyEx(key) followed by a series of ::RegSetValueEx(ValueName, ValueData). Unfortunately, I didn't have any Value Names for the list of strings to store. In other words, if I have 5 strings to write into the registry, I would need to generate 5 different Value Names to uniquely identify each string. Here's what the registry would look like:

Key:
SOFTWARE\Commpany\App\strings

Value Name and Value Data:
a = "string1"
b = "string2"
c = "string3"
d = "string4"
e = "string5"

The downside of this technique is the excessive number of Value Names, and the pseudo-random generation of those names. My original need of storing N strings would be better served by specifying only one Value Name along with a string list.

The technique I implemented consists of serializing a CStringList using MFCs CMemFile, CArchive and the registry's REG_BINARY data type. The registry is not the appropriate place to store massive amounts of data, and anything over 2K should be stored as a separate file outside the registry. Therefore, I placed a hard coded limit of 4096 bytes for the string list.

The code was tested using Microsoft Visual C++ 5.0sp3 under Windows 95.

// skip registry key opening sequence for clarity
const INT nSIZE = 4096;
DWORD dwType;
DWORD dwData  = nSIZE;
BYTE* bData   = (BYTE*)::calloc(nSIZE, sizeof(TCHAR));
ASSERT(bData);

const LONG retValue = ::RegQueryValueEx(hKey, pszValueName, NULL, &dwType,
bData, &dwData);

if(retValue == ERROR_SUCCESS and REG_BINARY == dwType){
ASSERT(dwData < nSIZE);
try{
  // Read
  CMemFile file(bData, nSIZE);
  CArchive ar(&file, CArchive::load);
  ar.m_bForceFlat = FALSE;
  ASSERT( ar.IsLoading() );
  CStringList myList;
  ASSERT( myList.IsSerializable() );
  myList.Serialize(ar);
  ar.Close();
  file.Close();

  myList.AddTail("Another string!");

  // Write
  file.Attach(bData, nSIZE, 16);
  CArchive ar2(&file, CArchive::store);
  ASSERT(myList.IsSerializable());
  myList.Serialize(ar);
  ar2.Close();
  const DWORD dwLen = file.GetLength();
  ASSERT(dwLen < nSIZE);
  ::RegSetValueEx(hKey, pszValueName, 0, REG_BINARY, file.Detach(), dwLen);
}
catch(CMemoryException* e){
  e->ReportError();
  e->Delete();
}
catch(CArchiveException* e){
  e->ReportError();
  e->Delete();
}
catch(CFileException* e){
  e->ReportError();
  e->Delete();
}
if(bData) free(bData); bData = NULL;
}

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