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Handling Error Information
Keep in mind that it is legal to return a status code only from the
implementation of an interface method sanctioned as legally returnable. Failure to
observe this rule invites the possibility of conflict between returned error code
values and those sanctioned by the application. In particular, pay attention to
this potential problem when propagating error codes from internally-Qcalled
functions.
Applications that call interfaces should treat any unknown returned error code
(as opposed to a success code) as synonymous with E_UNEXPECTED. This practice
of handling unknown error codes is required by clients of the OLE-defined
interfaces and APIs. Because typical programming practice is to handle a few
specific error codes in detail and treat the rest generically, this requirement of
handling unexpected or unknown error codes is easily met.
The following code sample shows the recommended way of handling unknown errors:
HRESULT hrErr;
hrErr = xxMethod();
switch (GetScode(hrErr)) {
case NOERROR:
//success
break;
case x1:
.
.
break;
case x2:
.
.
break;
case E_UNEXPECTED:
default:
//general failure
break;
}
The following error check is often used with those routines that don't return
anything special (other than S_OK or some unexpected error):
if (xxMethod() == NOERROR)
//success
else
//general failure;
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