The error_status_t keyword designates a type for an object that contains communication-status or fault-status information.
The error_status_t type is used as a part of the exception handling architecture in IDL. This type maps to an unsigned long. Applications that catch error situations have an out parameter or a return type of a procedure specified as error_status_t, and qualify the error_status_t with the comm_status or fault_status attributes in the ACF. If the parameter or return type was not qualified with the comm_status or fault_status attributes, then the parameter operates as though it were an unsigned long.
The MIDL 2.0 compiler generates stubs that contain the proper error handling architecture. However, earlier versions of the MIDL compiler handled a parameter or return type of error_status_t as though the comm_status and fault_status attributes were applied, even if they were not. With the MIDL 2.0 compiler, you must explicitly apply the comm_status and fault_status attributes to the parameter or procedure in the ACF.
The error_status_t type is one of the predefined types of the interface definition language. Predefined types can appear as type specifiers in typedef declarations, in general declarations, and in function declarators (either as the function-return-type or as parameter-type specifiers).
comm_status, fault_status, IDL