Windows Dev Center

ReportEvent function

Writes an entry at the end of the specified event log.


BOOL ReportEvent(
  _In_ HANDLE  hEventLog,
  _In_ WORD    wType,
  _In_ WORD    wCategory,
  _In_ DWORD   dwEventID,
  _In_ PSID    lpUserSid,
  _In_ WORD    wNumStrings,
  _In_ DWORD   dwDataSize,
  _In_ LPCTSTR *lpStrings,
  _In_ LPVOID  lpRawData


hEventLog [in]

A handle to the event log. The RegisterEventSource function returns this handle.

As of Windows XP with SP2, this parameter cannot be a handle to the Security log. To write an event to the Security log, use the AuthzReportSecurityEvent function.

wType [in]

The type of event to be logged. This parameter can be one of the following values.


Information event


Failure Audit event


Success Audit event


Error event


Information event


Warning event


For more information about event types, see Event Types.

wCategory [in]

The event category. This is source-specific information; the category can have any value. For more information, see Event Categories.

dwEventID [in]

The event identifier. The event identifier specifies the entry in the message file associated with the event source. For more information, see Event Identifiers.

lpUserSid [in]

A pointer to the current user's security identifier. This parameter can be NULL if the security identifier is not required.

wNumStrings [in]

The number of insert strings in the array pointed to by the lpStrings parameter. A value of zero indicates that no strings are present.

dwDataSize [in]

The number of bytes of event-specific raw (binary) data to write to the log. If this parameter is zero, no event-specific data is present.

lpStrings [in]

A pointer to a buffer containing an array of null-terminated strings that are merged into the message before Event Viewer displays the string to the user. This parameter must be a valid pointer (or NULL), even if wNumStrings is zero. Each string is limited to 31,839 characters.

Prior to Windows Vista:  Each string is limited to 32K characters.

lpRawData [in]

A pointer to the buffer containing the binary data. This parameter must be a valid pointer (or NULL), even if the dwDataSize parameter is zero.

Return value

If the function succeeds, the return value is nonzero, indicating that the entry was written to the log.

If the function fails, the return value is zero. To get extended error information, call GetLastError, which returns one of the following extended error codes.

Error codeMeaning

One of the parameters is not valid.

This error is returned on Windows Server 2003 if the message data to be logged is too large. This error is returned by the RPC server on Windows Server 2003 if the dwDataSize parameter is larger than 261,991 (0x3ff67).


Insufficient memory resources are available to complete the operation.


The array bounds are invalid.

This error is returned if the message data to be logged is too large. On Windows Vista and later, this error is returned if the dwDataSize parameter is larger than 61,440 (0xf000).


The stub received bad data.

This error is returned on Windows XP if the message data to be logged is too large. This error is returned by the RPC server on Windows XP, if the dwDataSize parameter is larger than 262,143 (0x3ffff).


Use FormatMessage to obtain the message string for the returned error.



This function is used to log an event. The entry is written to the end of the configured log for the source identified by the hEventLog parameter. The ReportEvent function adds the time, the entry's length, and the offsets before storing the entry in the log. To enable the function to add the user name, you must supply the user's SID in the lpUserSid parameter.

There are different size limits on the size of the message data that can be logged depending on the version of Windows used by both the client where the application is run and the server where the message is logged. The server is determined by the lpUNCServerName parameter passed to the RegisterEventSource function. Different errors are returned when the size limit is exceeded that depend on the version of Windows.

If the string that you log contains %n, where n is an integer value (for example, %1), the event viewer treats it as an insertion string. Because an IPv6 address can contain this character sequence, you must provide a format specifier (!S!) to log an event message that contains an IPv6 address. This specifier tells the formatting code to use the string literally and not perform any further expansions (for example, "my IPv6 address is: %1!S!").


For an example, see Reporting an Event.


Minimum supported client

Windows 2000 Professional [desktop apps only]

Minimum supported server

Windows 2000 Server [desktop apps only]


Winbase.h (include Windows.h)





Unicode and ANSI names

ReportEventW (Unicode) and ReportEventA (ANSI)

See also

Event Logging Functions
Event Log File Format



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