HRESULT类型返回值
HRESULT类型返回值
HRESULT的定义
HRESULT定义在winnt.h中，把HRESULT当成LONG算了（32位，8个字节）。
#ifndef _HRESULT_DEFINED
#define _HRESULT_DEFINED
#ifdef __midl
typedef LONG HRESULT;
#else
typedef __success(return >= 0) long HRESULT;
#endif // __midl
#endif // !_HRESULT_DEFINED
HRESULT的含义是Here’s the Result。H代表Here，真是个奇葩。
HRESULT的结构
在winerror.h中对HRESULT的说明：
//
// Note: There is a slightly modified layout for HRESULT values below,
// after the heading "COM Error Codes".
//
// Values are 32 bit values laid 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
// +---+-+-+-----------------------+-------------------------------+
// |Sev|C|R| Facility | Code |
// +---+-+-+-----------------------+-------------------------------+
//
// where
//
// Sev - is the severity code
//
// 00 - Success
// 01 - Informational
// 10 - Warning
// 11 - Error
//
// C - is the Customer code flag
//
// R - is a reserved bit
//
// Facility - is the facility code
//
// Code - is the facility's status code
//
COM Error Codes:
//
// The return value of COM functions 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
//
HRESULT类型返回值
"HRESULT类型返回值的处理： 对于返回值类型为HRESULT的函数，用SUCCEEDED宏来判断是否成功，不能直接判断返回值是否等于S_OK。 原因：部分函数可能返回大于0的数值。只判断是否等于S_OK，会误把某些执行正常的函数调用当成失败。"
判断函数调用成功与否不能简单地将返回值与S_OK或E_NOINTERFACE等进行比较，而是要使用FAILED/SUCCEEDED宏
//
// Generic test for success on any status value (non-negative numbers
// indicate success).
//
#define SUCCEEDED(hr) (((HRESULT)(hr)) >= 0)
//
// and the inverse
//
#define FAILED(hr) (((HRESULT)(hr)) < 0)
还有这个错误定义
//
// Severity values
//
#define SEVERITY_SUCCESS 0
#define SEVERITY_ERROR 1
HRESULT类型的返回值判断
HRESULT类型不能仅仅用FAILED/SUCCEEDED判断，要参照对应API文档
//
// Success codes
//
#define S_OK ((HRESULT)0L)
#define S_FALSE ((HRESULT)1L)
自定义HRESULT返回值
使用命令行查看Window错误码含义
命令语法：‘net helpmsg [error value]’。
net helpmsg 2