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IDebugDocumentChecksum2::GetChecksumAndAlgorithmId

  • Article

Retrieves the document checksum and algorithm identifier given the maximum number of bytes to use.

Syntax

public int GetChecksumAndAlgorithmId(
    out Guid pRetVal,
    uint     cMaxBytes,
    out byte pChecksum,
    out uint pcNumBytes
);

Parameters

pRetVal
[out] Unique identifier for the checksum algorithm.

cMaxBytes
[in] Maximum number of bytes to be used for the checksum.

pChecksum
[out] Value of the checksum.

pcNumBytes
[out] Actual number of bytes used for the checksum.

Return Value

If successful, returns S_OK; otherwise, returns an error code.

Example

The following example uses this method to get the checksum and algorithm for a document.

HRESULT CDebugCodeContext::GetDocumentChecksumAndAlgorithmId(GUID *pguidAlgorithm, BYTE **ppChecksum, ULONG *pcNumBytes)
{
    HRESULT hRes = E_FAIL;

    *ppChecksum = NULL;
    *pcNumBytes = 0;

    CComPtr<IDebugDocumentContext2> pDocContext;

    hRes = this->GetDocumentContext(&pDocContext);

    if ( HREVAL(S_OK, hRes) )
    {
        CComQIPtr<IDebugDocumentChecksum2> pDocChecksum(pDocContext);

        if ( pDocChecksum != NULL )
        {
            // Figure out the size of the checksum buffer required
            ULONG cNumBytes = 0;

            hRes = pDocChecksum->GetChecksumAndAlgorithmId(pguidAlgorithm, 0, NULL, &cNumBytes);

            if ( S_OK == hRes )
            {
                // check to see if we got back valid values
                if ( cNumBytes && GUID_NULL != (*pguidAlgorithm) )
                {
                    // Alloc space for the checksum data
                    BYTE *pChecksum = (BYTE*) CoTaskMemAlloc(cNumBytes);

                    if ( pChecksum )
                    {
                        // Get the buffer containing the checksum info
                        hRes = pDocChecksum->GetChecksumAndAlgorithmId(pguidAlgorithm, cNumBytes, pChecksum, &cNumBytes);

                        if ( HREVAL(S_OK, hRes) )
                        {
                            *ppChecksum = pChecksum;
                            *pcNumBytes = cNumBytes;
                        }
                        else
                        {
                            CoTaskMemFree(pChecksum);
                        }
                    }
                    else
                        hRes = E_OUTOFMEMORY;
                }
                else
                    hRes = S_FALSE; // lang doesn't support checksums
            }
            else
                hRes = S_FALSE; // failed to work out checksum info
        }
        else
            hRes = S_FALSE; // SH doesn't support checksums
    }

    return ( hRes );
}

See also