Loading image files from a database, using ADO

Introduction
Putting and retrieving image files in to a database, is not a simple task. I you want to look on the Internet for such a sample, you will be surprised that there is no C++ sample for that. There is only information, that you have to use the Safearray, SetChunk, and GetChunk methods.

This article will show how you can put image files in to a database via ADO, as well as how you can retrieve them. With this example, you can use any file format such as Word, Excel etc., not just image file formats.

Implementation
The example contains two methods for putting and retrieving image files to and from a database. The first method retrieves data from the database, create a file in a temporary directory, and puts the data into a file created. The parameter strImageName is the name of the file that will be created. The second parameter indicates the ADO field object containing the image data.

The following code sample shows the implementation:

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CString CADOImageDBDlg::GetImageFromADO(CString
strImageName, FieldPtr pField)
{
//Creating temp file
char tmpPath[_MAX_PATH+1];
GetTempPath(_MAX_PATH,tmpPath);
strImageName.Insert(0,tmpPath);
CFile outFile(strImageName,
CFile::modeCreate|CFile::modeWrite);

//Helper variable for retrieving image data
unsigned char* lpData = NULL;
long lngOffSet = 0;
long lngSize=pField->ActualSize;
const long ChunkSize=50;
_variant_t varChunk;
UCHAR chData;
HRESULT hr;
long lBytesCopied = 0;
lpData=new unsigned char [lngSize];

//Retrieveing data from vararray
while(lngOffSet < lngSize)
{
try
{
//Get 50 size long chunk from database
varChunk = pField->GetChunk(ChunkSize);

//putting chunk in to safe array
for(long lIndex = 0; lIndex <=
(ChunkSize - 1); lIndex++)
{
hr=
SafeArrayGetElement(varChunk.parray,
&lIndex, &chData);
if(SUCCEEDED(hr))
{
((UCHAR*)lpData)[lBytesCopied] = chData;
lBytesCopied++;
}
else
break;
}
lngOffSet += ChunkSize;
}
catch(_com_error &e)
{
dump_com_error(e);
return FALSE;
}
}

//
LPSTR buffer = (LPSTR)GlobalLock(lpData);
// write data in to file
outFile.Write(lpData,lngSize);

// free reserved data
GlobalUnlock(lpData);
delete lpData;

//Return full path file
return strImageName;
}

bool CADOImageDBDlg::PutImageInADO(CString
strFilePath,FieldPtr pFileData)
{
//Opent File
CFile fileImage;
CFileStatus fileStatus;
fileImage.Open(strFilePath, CFile::modeRead);
fileImage.GetStatus(fileStatus);

//Alocating memory for data
ULONG nBytes = (ULONG)fileStatus.m_size;
HGLOBAL hGlobal = GlobalAlloc(GPTR,nBytes);
LPVOID lpData = GlobalLock(hGlobal);

//Putting data in to file
fileImage.Read(lpData,nBytes);


HRESULT hr;
_variant_t varChunk;
long lngOffset = 0;
UCHAR chData;
SAFEARRAY FAR *psa = NULL;
SAFEARRAYBOUND rgsabound[1];

try
{
//Create a safe array to
//store the array of BYTES
rgsabound[0].lLbound = 0;
rgsabound[0].cElements = nBytes;
psa = SafeArrayCreate(VT_UI1,1,rgsabound);

while(lngOffset < (long)nBytes)
{
chData = ((UCHAR*)lpData)[lngOffset];
hr = SafeArrayPutElement(psa,
&lngOffset, &chData);

if(hr!=S_OK)
return false;

lngOffset++;
}
lngOffset = 0;

//Assign the Safe array to a variant.
varChunk.vt = VT_ARRAY|VT_UI1;
varChunk.parray = psa;

hr = pFileData->AppendChunk(varChunk);

if(hr!=S_OK)
return false;
}
catch(_com_error &e)
{
dump_com_error(e);
return FALSE;
}

//Free memory
GlobalUnlock(lpData);
return true;
}For image display, I created a class which wraps the freeimage library.

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