Have you confirmed that the pBuffer that would read out is byte for byte
the same as the bmBytes that you used to insert in to the database? If
they are the same, then sqlite did its job (or rather you called it
correctly...), and the trouble is somewhere else.
David
On Fri, 2008-08-29 at 14:13 -0400, Jared Miller wrote:
> Hello,
>
> I am having trouble figuring out how to successfully write an image to the
> SQLite database as a Blob, using C++.
>
> I have an HBITMAP that I would like to be able to store to and retrieve from
> the DB. If I understand what I have read correctly, I am supposed to write
> out the actual byte data to the DB. Here is what I have done so far.
>
> I pass in pbyBitmap as the bmBytes parameter to this function:
> ImportPageImage(CPage* pPage, BYTE* bmBytes, DWORD bmSize), which calls the
> code below. . .
>
> //prepare query
> static const WCHAR tblInsertBlob[] = _T("Insert into [tblBlob] ([Data])
> values (?)");
> SQL_HANDLE blobHandle = m_pSqliteDB->PrepareQuery16(tblInsertBlob); //calls
> sqlite3_prepare16()
>
> //bind blob
> m_pSqliteDB->BindBlob(blobHandle, 1, (void *)bmBytes, bmSize); //calls
> sqlite3_bind_blob (bmBytes is the pData param)
>
> Then I call StepQuery to execute it, and then I close the query.
> sqlite3_bind_blob() returns SQLITE_OK when I run it, so it does not seem to
> be encountering an error there.
>
> Something apparently gets written to the database, but it does not seem to be
> correct. When I try to retrieve and display my image, it is all black (which
> is how bitmaps look when there is no data).
>
> I think that the problem is coming from writing the BLOB to the database, but
> I am not entirely sure. Just in case it is getting written properly and I am
> not reading it from the database correctly, I will show you how I pulled it
> from the DB.
>
> //prepare blob
> sqlite3_blob* pBlob = NULL;
> sqlite3_blob_open(m_sqliteDB, "main", "tblBlob", "Data", iBlobID, FALSE,
> &pBlob);
>
> BLOB_HANDLE hBlob = pBlob;
> int size = sqlite3_blob_bytes(hBlob); //works correctly, returns 998058
> BYTE* pBuffer = g_MemMgr.AllocDataBuffer(size);
>
> sqlite3_blob_read(hBlob, pBuffer, size, 0); //returns SQLITE_OK
> sqlite3_blob_close(hBlob);
>
> I then try to make a bitmap out of the bytes in pBuffer, but when I do, it
> turns out all black (as I mentioned earlier).
>
> Do I have the concept correct? And if so, what part of my current code should
> I change to be able to use my DB to store image data?
>
> Thanks a lot.
>
>
>
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