COM Error---HRESULT

一、COM Error

调用COM接口产生的错误。几乎所有的COM函数和接口方法都返回类型为HRESULT的值。HRESULT（用于结果句柄）是返回成功、警告和错误值的一种方法。HRESULTs实际上不是任何事物的句柄；它们只是值中有几个字段编码的值。根据COM规范，结果为零表示成功，非零表示失败。

二、COM Error Code（HRESULT）

也是一个32bit的值，大多数的值也是定义了默认的错误消息。它的构成如下

S (1 bit):严重程度，1为失败，0为成功

R (1 bit): 如果N=0，必须设置为1，N=0，该位被NTSTATUS定义

C (1 bit): 是否是客户定义，还是微软定义的错误.1是客户定制

N (1 bit): 标识是否是一个NTSTATUS的值，0的话可以把NTSTATUS值映射为一个HRESULT值

X (1 bit):  保留位，永远是0

Facility (11 bits)：错误来源，取值如下

Value	Meaning
FACILITY_NULL 0	The default facility code.
FACILITY_RPC 1	The source of the error code is an RPC subsystem.
FACILITY_DISPATCH 2	The source of the error code is a COM Dispatch.
FACILITY_STORAGE 3	The source of the error code is OLE Storage.
FACILITY_ITF 4	The source of the error code is COM/OLE Interface management.
FACILITY_WIN32 7	This region is reserved to map undecorated error codes into HRESULTs.
FACILITY_WINDOWS 8	The source of the error code is the Windows subsystem.
FACILITY_SECURITY 9	The source of the error code is the Security API layer.
FACILITY_SSPI 9	The source of the error code is the Security API layer.
FACILITY_CONTROL 10	The source of the error code is the control mechanism.
FACILITY_CERT 11	The source of the error code is a certificate client or server?
FACILITY_INTERNET 12	The source of the error code is Wininet related.
FACILITY_MEDIASERVER 13	The source of the error code is the Windows Media Server.
FACILITY_MSMQ 14	The source of the error code is the Microsoft Message Queue.
FACILITY_SETUPAPI 15	The source of the error code is the Setup API.
FACILITY_SCARD 16	The source of the error code is the Smart-card subsystem.
FACILITY_COMPLUS 17	The source of the error code is COM+.
FACILITY_AAF 18	The source of the error code is the Microsoft agent.
FACILITY_URT 19	The source of the error code is .NET CLR.
FACILITY_ACS 20	The source of the error code is the audit collection service.
FACILITY_DPLAY 21	The source of the error code is Direct Play.
FACILITY_UMI 22	The source of the error code is the ubiquitous memoryintrospection service.
FACILITY_SXS 23	The source of the error code is Side-by-side servicing.
FACILITY_WINDOWS_CE 24	The error code is specific to Windows CE.
FACILITY_HTTP 25	The source of the error code is HTTP support.
FACILITY_USERMODE_COMMONLOG 26	The source of the error code is common Logging support.
FACILITY_USERMODE_FILTER_MANAGER 31	The source of the error code is the user mode filter manager.
FACILITY_BACKGROUNDCOPY 32	The source of the error code is background copy control
FACILITY_CONFIGURATION 33	The source of the error code is configuration services.
FACILITY_STATE_MANAGEMENT 34	The source of the error code is state management services.
FACILITY_METADIRECTORY 35	The source of the error code is the Microsoft Identity Server.
FACILITY_WINDOWSUPDATE 36	The source of the error code is a Windows update.
FACILITY_DIRECTORYSERVICE 37	The source of the error code is Active Directory.
FACILITY_GRAPHICS 38	The source of the error code is the graphics drivers.
FACILITY_SHELL 39	The source of the error code is the user Shell.
FACILITY_TPM_SERVICES 40	The source of the error code is the Trusted Platform Module services.
FACILITY_TPM_SOFTWARE 41	The source of the error code is the Trusted Platform Module applications.
FACILITY_PLA 48	The source of the error code is Performance Logs and Alerts
FACILITY_FVE 49	The source of the error code is Full volume encryption.
FACILITY_FWP 50	he source of the error code is the Firewall Platform.
FACILITY_WINRM 51	The source of the error code is the Windows Resource Manager.
FACILITY_NDIS 52	The source of the error code is the Network Driver Interface.
FACILITY_USERMODE_HYPERVISOR 53	The source of the error code is the Usermode Hypervisor components.
FACILITY_CMI 54	The source of the error code is the Configuration Management Infrastructure.
FACILITY_USERMODE_VIRTUALIZATION 55	The source of the error code is the user mode virtualization subsystem.
FACILITY_USERMODE_VOLMGR 56	The source of the error code is  the user mode volume manager
FACILITY_BCD 57	The source of the error code is the Boot Configuration Database.
FACILITY_USERMODE_VHD 58	The source of the error code is user mode virtual hard disk support.
FACILITY_SDIAG 60	The source of the error code is System Diagnostics.
FACILITY_WEBSERVICES 61	The source of the error code is the Web Services.
FACILITY_WINDOWS_DEFENDER 80	The source of the error code is a Windows Defender component.
FACILITY_OPC 81	The source of the error code is the open connectivity service.

Code (2 bytes): 结果码，有一部分值是从Win32 Error Code和NTSTATUS继承来的。

在源代码级别，所有错误值都由三部分组成，由下划线分隔。第一部分是识别与错误相关联的设施的前缀，第二部分是E表示错误，第三部分是描述实际情况的字符串。例如，当硬盘上没有剩余空间时，会返回STG_E_MEDIUMFULL。stg前缀表示存储设备，e表示状态代码表示错误，MEDIUMFULL提供有关错误的特定信息。

三、HRESULT

3.1、HRESULT的定义

在头文件winnt.h里，HRESULT定义如下：

// Component Object Model defines, and macros
#ifndef _HRESULT_DEFINED
#define _HRESULT_DEFINED
typedef LONG HRESULT;
#endif // !_HRESULT_DEFINED

值就是COM Error Code。

3.2、获取和检测

从定义可以看到 HRESULT被定义为了LONG型，也就是把COM Error Code当成一个4字节的有符号数来处理，这样一来就可以把Error Code的最高位S当成符号位，0时是正数，1时是负数，当我们调用COM接口，就可以用下面的宏来检测COM接口的返回值

#define SUCCEEDED(Status) ((HRESULT)(Status) >= 0)
#define FAILED(Status) ((HRESULT)(Status) <0)

成功的代码有多个，失败的代码也有多个，一个COM接口在各种情况下返回的状态代码通常将包含多个成功代码及多个失败代码。这就是我们为什么要使用SUCCEEDED及FAILED宏的原因。一般不能直接将HRESULT值同某个成功代码（如S_OK）进行比较以决定某个函数是否成功。

3.3、获取错误消息

也是通过这个函数来获取

DWORD WINAPI FormatMessage (

                            DWORD dwFlags, // source and processing options

                            LPCVOID lpSource, // message source

                            DWORD dwMessageId, // message identifier

                            DWORD dwLanguageId, // language identifier

                            LPTSTR lpBuffer, // message buffer

                            DWORD nSize, // maximum size of message buffer

                            va_list *Arguments // array of message inserts

 

                            );