Opening an Attachment

Opening an attachment involves displaying its data. For example, when a file attachment is opened, the contents of the file are displayed. Whereas messages and folders are opened using their entry identifiers, attachments are opened using their attachment numbers — PR_ATTACH_NUM properties. Attachment numbers are available through a message's attachment table.

To open all attachments in a message

1. Call the message's IMessage::GetAttachmentTable method to access its attachment table.
2. Call HrQueryAllRows to retrieve all the rows in the table.
3. For each row:
   1. Open the attachment by passing the attachment number represented in the PR_ATTACH_NUM column in a call to the message's IMessage::OpenAttach method. OpenAttach returns a pointer to an IAttach implementation that provides access to attachment properties.
   2. Call the attachment's IMAPIProp::GetProps method to retrieve its PR_ATTACH_METHOD property.
   3. If PR_ATTACH_METHOD is set to ATTACH_BY_REF_ONLY, call IMAPIProp::GetProps to retrieve the PR_ATTACH_PATHNAME property.
   4. If PR_ATTACH_METHOD is set to ATTACH_BY_VALUE, call IMAPIProp::OpenProperty to open the PR_ATTACH_DATA_BIN property with the IStream interface. See the sample code following this procedure.
   5. If PR_ATTACH_METHOD is set to ATTACH_OLE and the attachment is an OLE 2 object:

6. If PR_ATTACH_METHOD is set to ATTACH_EMBEDDED_MSG, it is not unusual for the value of PR_ATTACH_DATA_OBJ to contain an error. This is because you and the table implementer have no way to agree on the type of object to return. To retrieve a pointer to the attached message, open the attachment using IMessage::OpenAttach. Then access the attachment data by calling its IMAPIProp::OpenProperty method.

You can request that an attachment is opened in read/write or read-only mode. Read-only is the default mode, and many message store providers open all attachments in this mode regardless of what clients request. Pass the MAPI_BEST_ACCESS flag to request that the message store provider grant the highest level of access it can and then retrieve the open attachment's PR_ACCESS_LEVEL property to determine the level of access that was actually granted.

The following example shows how to open the data in an attachment's PR_ATTACH_DATA_BIN property. It allocates pointers to two streams: one for the file and one for the attachment. The OpenStreamOnFile function opens the file stream in read-only mode. The call to the attachment's IMAPIProp::OpenProperty method opens the attachment stream in read/write mode. The code then copies from the file stream to the attachment stream and releases both streams.

LPSTREAM pStreamFile, pStreamAtt;
HRESULT hr;

hr = OpenStreamOnFile (MAPIAllocateBuffer, MAPIFreeBuffer,
                       STGM_READ, "myfile.doc", NULL, &pStreamFile);
if (HR_SUCCEEDED(hr))
{
    // Open the destination stream in the attachment object
    hr = pAttach->OpenProperty (PR_ATTACH_DATA_BIN,
                                &IID_IStream,
                                0,
                                MAPI_MODIFY | MAPI_CREATE,
                                (LPUNKNOWN *)&pStreamAtt);
    if (HR_SUCCEEDED(hr))
    {
        STATSTG StatInfo;
        pStreamFile->Stat (&StatInfo, STATFLAG_NONAME);
        hResult = pStreamFile->CopyTo (pStreamAtt, StatInfo.cbSize, 
                                       NULL, NULL);
        pStreamAtt->Release();
    }
    pStreamFile->Release();
}