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nf-winbase-readeventloga.md

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UID title description helpviewer_keywords old-location tech.root ms.assetid ms.date ms.keywords req.header req.include-header req.target-type req.target-min-winverclnt req.target-min-winversvr req.kmdf-ver req.umdf-ver req.ddi-compliance req.unicode-ansi req.idl req.max-support req.namespace req.assembly req.type-library req.lib req.dll req.irql targetos req.typenames req.redist ms.custom f1_keywords dev_langs topic_type api_type api_location api_name req.apiset
NF:winbase.ReadEventLogA
ReadEventLogA function (winbase.h)
Reads the specified number of entries from the specified event log. (ANSI)
EVENTLOG_BACKWARDS_READ
EVENTLOG_FORWARDS_READ
EVENTLOG_SEEK_READ
EVENTLOG_SEQUENTIAL_READ
ReadEventLogA
winbase/ReadEventLogA
base\readeventlog.htm
base
10b37174-661a-4dc6-a7fe-752739494156
12/05/2018
EVENTLOG_BACKWARDS_READ, EVENTLOG_FORWARDS_READ, EVENTLOG_SEEK_READ, EVENTLOG_SEQUENTIAL_READ, ReadEventLog, ReadEventLog function, ReadEventLogA, ReadEventLogW, _win32_readeventlog, base.readeventlog, winbase/ReadEventLog, winbase/ReadEventLogA, winbase/ReadEventLogW
winbase.h
Windows.h
Windows
Windows 2000 Professional [desktop apps only]
Windows 2000 Server [desktop apps only]
ReadEventLogW (Unicode) and ReadEventLogA (ANSI)
Advapi32.lib
Advapi32.dll
Windows
19H1
ReadEventLogA
winbase/ReadEventLogA
c++
APIRef
kbSyntax
DllExport
Advapi32.dll
Ext-MS-Win-AdvAPI32-EventLog-L1-1-0.dll
Ext-Ms-Win-AdvAPI32-EventLog-Ansi-L1-1-0.dll
Ext-Ms-Win-AdvAPI32-EventLog-L1-1-1.dll
ReadEventLog
ReadEventLogA
ReadEventLogW
ext-ms-win-advapi32-eventlog-ansi-l1-1-0 (introduced in Windows 10, version 10.0.10240)

ReadEventLogA function

-description

Reads the specified number of entries from the specified event log. The function can be used to read log entries in chronological or reverse chronological order.

-parameters

-param hEventLog [in]

A handle to the event log to be read. The OpenEventLog function returns this handle.

-param dwReadFlags [in]

Use the following flag values to indicate how to read the log file. This parameter must include one of the following values (the flags are mutually exclusive).

Value Meaning
EVENTLOG_SEEK_READ
0x0002
Begin reading from the record specified in the dwRecordOffset parameter.

This option may not work with large log files if the function cannot determine the log file's size. For details, see Knowledge Base article, 177199.

EVENTLOG_SEQUENTIAL_READ
0x0001
Read the records sequentially.

If this is the first read operation, the EVENTLOG_FORWARDS_READ EVENTLOG_BACKWARDS_READ flags determines which record is read first.

 

You must specify one of the following flags to indicate the direction for successive read operations (the flags are mutually exclusive).

Value Meaning
EVENTLOG_FORWARDS_READ
0x0004
The log is read in chronological order (oldest to newest).

The default.

EVENTLOG_BACKWARDS_READ
0x0008
The log is read in reverse chronological order (newest to oldest).

-param dwRecordOffset [in]

The record number of the log-entry at which the read operation should start. This parameter is ignored unless dwReadFlags includes the EVENTLOG_SEEK_READ flag.

-param lpBuffer [out]

An application-allocated buffer that will receive one or more EVENTLOGRECORD structures. This parameter cannot be NULL, even if the nNumberOfBytesToRead parameter is zero.

The maximum size of this buffer is 0x7ffff bytes.

-param nNumberOfBytesToRead [in]

The size of the lpBuffer buffer, in bytes. This function will read as many log entries as will fit in the buffer; the function will not return partial entries.

-param pnBytesRead [out]

A pointer to a variable that receives the number of bytes read by the function.

-param pnMinNumberOfBytesNeeded [out]

A pointer to a variable that receives the required size of the lpBuffer buffer. This value is valid only if this function returns zero and GetLastError returns ERROR_INSUFFICIENT_BUFFER.

-returns

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. To get extended error information, call GetLastError.

-remarks

When this function returns successfully, the read position in the event log is adjusted by the number of records read.

Note  The configured file name for this source may also be the configured file name for other sources (several sources can exist as subkeys under a single log). Therefore, this function may return events that were logged by more than one source.
 

Examples

For an example, see Querying for Event Information.

Note

The winbase.h header defines ReadEventLog as an alias which automatically selects the ANSI or Unicode version of this function based on the definition of the UNICODE preprocessor constant. Mixing usage of the encoding-neutral alias with code that not encoding-neutral can lead to mismatches that result in compilation or runtime errors. For more information, see Conventions for Function Prototypes.

-see-also

ClearEventLog

CloseEventLog

EVENTLOGRECORD

Event Logging Functions

OpenEventLog

ReportEvent