HRESULT -- Structure of COM Error Codes
SCODEs on 16-bit platforms are divided into four fields: a severity code, a context field, a facility field, and an error code. The following illustration shows the format of an SCODE on a 16-bit platform; the numbers indicate bit positions:
HRESULTs and SCODEs on 32-bit platforms have the following format:
The high-order bit in the HRESULT or SCODE indicates whether the return value represents success or failure. If set to 0, SEVERITY_SUCCESS, the value indicates success. If set to 1, SEVERITY_ERROR, it indicates failure.
The context field is reserved in the SCODE on 16-bit platforms and does not exist in the version for 32-bit platforms. The R, C, N, and r bits are also reserved.
The facility field in both versions indicates the system service responsible for the error. Microsoft allocates new facility codes as they become necessary. Most SCODEs and HRESULTs set the facility field to FACILITY_ITF, indicating an interface method error.
vc6中的说明(in winerror.h line:7860)
////////////////////////////////////
// //
// OLE Error Codes //
// //
////////////////////////////////////
//
// OLE error definitions and values
//
// The return value of OLE APIs and methods is an HRESULT.
// This is not a handle to anything, but is merely a 32-bit value
// with several fields encoded in the value. The parts of an
// HRESULT are shown below.
//
// Many of the macros and functions below were orginally defined to
// operate on SCODEs. SCODEs are no longer used. The macros are
// still present for compatibility and easy porting of Win16 code.
// Newly written code should use the HRESULT macros and functions.
//
//
// HRESULTs are 32 bit values layed out as follows:
//
// 3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1
// 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
// +-+-+-+-+-+---------------------+-------------------------------+
// |S|R|C|N|r| Facility | Code |
// +-+-+-+-+-+---------------------+-------------------------------+
//
// where
//
// S - Severity - indicates success/fail
//
// 0 - Success
// 1 - Fail (COERROR)
//
// R - reserved portion of the facility code, corresponds to NT's
// second severity bit.
//
// C - reserved portion of the facility code, corresponds to NT's
// C field.
//
// N - reserved portion of the facility code. Used to indicate a
// mapped NT status value.
//
// r - reserved portion of the facility code. Reserved for internal
// use. Used to indicate HRESULT values that are not status
// values, but are instead message ids for display strings.
//
// Facility - is the facility code
//
// Code - is the facility's status code
//
Common facility fields are described in the following table.
| Facility Field | Value | Description |
| FACILITY_DISPATCH | 2 | For late-binding IDispatch interface errors. |
| FACILITY_ITF |
4 | For most status codes returned from interface methods. The actual meaning of the error is defined by the interface. That is, two HRESULTs with exactly the same 32-bit value returned from two different interfaces might have different meanings. |
| FACILITY_NULL | 0 | For broadly applicable common status codes such as S_OK. |
| FACILITY_RPC | 1 | For status codes returned from remote procedure calls. |
| FACILITY_STORAGE | 3 | For status codes returned from IStorage or IStream method calls relating to structured storage. Status codes whose code (lower 16 bits) value is in the range of DOS error codes (that is, less than 256) have the same meaning as the corresponding DOS error. |
| FACILITY_WIN32 | 7 | Used to provide a means of handling error codes from functions in the Win32 API as an HRESULT. Error codes in 16-bit OLE that duplicated Win32 error codes have also been changed to FACILITY_WIN32. |
| FACILITY_WINDOWS | 8 | Used for additional error codes from Microsoft-defined interfaces. |
| VC6中的定义 | ||
| FACILITY_SSPI | 9 | |
| FACILITY_SETUPAPI | 15 | |
| FACILITY_CONTROL | 10 | |
| FACILITY_CERT | 11 | |
| FACILITY_INTERNET | 12 | |
| FACILITY_MEDIASERVER | 13 | |
| FACILITY_MSMQ | 14 |
The code field is a unique number that is assigned to represent the error or warning.
By convention, HRESULTs generally have names in the following format:
Facility_Severity_Reason
Facility is either the facility name or some other distinguishing identifier; Severity is a single letter, S or E, that indicates whether the function call succeeded (S) or produced an error (E); and Reason is an identifier that describes the meaning of the code. For example, the status code STG_E_FILENOTFOUND indicates a storage-related error has occurred; specifically, a requested file does not exist. Status codes from FACILITY_NULL omit the Facility_ prefix.
Error codes are defined within the context of an interface implementation. Once defined, success codes cannot be changed or new success codes added. However, new failure codes can be written. Microsoft reserves the right to define new failure codes (but not success codes) for the interfaces described in FACILITY_ITF or in new facilities.