In this CASE clause, the value returned from GetBlob is cast to the LPCTSTR variable pStr. If it is not null, the return value in the PBCallInfo structure is set to the value of the blob:

case pbvalue_blob:
   pStr = (LPCTSTR)Session-> GetBlob(retVal.blob_val);
   if (strncmp(pStr, "null", 4)==0 )
      ci -> returnValue ->SetToNull();
   else
      {
         ci -> returnValue->SetBlob(retVal.blob_val);
         Session -> ReleaseValue(retVal);
      }
   break;