With few exceptions, every iMesh function includes an output argument, 'int *err', which returns an error code indicating if the function call may have failed. If the value returned for the 'err' argument is NOT iBase_SUCCESS, the caller should NOT attempt to interpret (read the values in) any of the other return arguments of the call. While some implementations may actually return valid/useful results in other return arguments of a call that has failed, there is no guarentee that ALL implementations will do similarly and so depending on such behavior is neither portable nor safe. This is true even if the returned values are different from the values of the arguments before the call was made.