Loading image files from a database, using ADO






4.74/5 (21 votes)
Putting and retrieving images files to and from a database, via 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:
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.
Update history
- 1.0.0.119 - January 27, 2006 - First release version.