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PdhVbOpenLog function

The PdhVbOpenLog function opens the specified log file for reading and writing. This function calls PdhOpenLog.

Function PdhVbOpenLog( _ ByVal szLogFileName As LPCTSTR, _ ByVal dwAccessFlags As DWORD, _ ByVal lpdwLogType As LPDWORD, _ ByVal hQuery As PDH_HQUERY, _ ByVal dwMaxSize As DWORD, _ ByVal szUserCaption As LPCSTR, _ ByRef phLog As PDH_HLOG _ ) As DWORD

Parameters

szLogFileName [in]

Pointer to a string that specifies the name of the log file to be opened.

If the log file contains SQL data, the format of the name of the log file is SQL:DataSourceName!LogFileName. In this case, the value of the lpdwLogType parameter is PDH_LOG_TYPE_SQL.

dwAccessFlags [in]

Type of access to be specified when the log file is opened. This parameter can be one of the following values.

ValueMeaning
PDH_LOG_READ_ACCESS

A log file is opened for a read operation.

PDH_LOG_WRITE_ACCESS

A new log file is opened for a write operation.

PDH_LOG_UPDATE_ACCESS

An existing log file is opened for a write operation.

 

The value selected from the previous table can be combined using the OR operator with one of the following create access flags.

ValueMeaning
PDH_LOG_CREATE_NEW

A new log file with the specified name is created.

PDH_LOG_CREATE_ALWAYS

A new log file with the specified name is created and any existing log file with the same name is erased.

PDH_LOG_OPEN_EXISTING

An existing log file with the specified name is opened. If a log file with the specified name does not exist, this is equal to PDH_LOG_CREATE_NEW.

PDH_LOG_OPEN_ALWAYS

An existing log file with the specified name is opened or a new log file with the specified name is created.

 

lpdwLogType [in]

Pointer to a variable that indicates the type of log file to be opened. This parameter can be one of the following values.

ValueMeaning
PDH_LOG_TYPE_UNDEFINED

Undefined log file format.

PDH_LOG_TYPE_CSV

Text files containing column headers in the first line, and individual data samples in each subsequent line.

PDH_LOG_TYPE_SQL

The data in the log file is in SQL.

PDH_LOG_TYPE_TSV

Same as PDH_LOG_TYPE_CSV.

PDH_LOG_TYPE_BINARY

Binary log file format. Includes circular log files.

PDH_LOG_TYPE_PERFMON

Perfmon log file format.

 

hQuery [in]

Query handle. This handle is returned by the PdhVbOpenQuery function.

This parameter can be NULL if the log file is to be opened for reading.

dwMaxSize [in]

Maximum size of the log file, in bytes. This value is used only if the log file is a limited-size or circular log file.

szUserCaption [in]

Pointer to a string that specifies the user-defined caption of the log file. A log file caption generally describes the contents of the log file. When an existing log file is opened, the value of this parameter is ignored.

phLog [in, ref]

Pointer to a buffer that receives a handle to the opened log file.

Return value

If the function succeeds, it returns 0.

If the function fails, the return value is a system error code or a PDH error code. The following are possible values.

Return codeDescription
PDH_INSUFFICIENT_BUFFER

The requested data is larger than the buffer supplied. Unable to return the requested data.

PDH_INVALID_ARGUMENT

One or more of the string buffers is not the correct size.

PDH_INVALID_HANDLE

The handle is not a valid PDH object.

PDH_LOG_FILE_OPEN_ERROR

Unable to open the specified log file.

PDH_FILE_NOT_FOUND

Unable to find the specified file.

 

Remarks

When using this function to write performance data to a log file, a query must first be opened using PdhVbOpenQuery.

There must be a currently opened query, and the desired counters must be added to it, before this function is called.

Note that log files in the Perfmon format can only be opened for reading.

Requirements

Minimum supported client

Windows XP [desktop apps only]

Minimum supported server

Windows Server 2003 [desktop apps only]

Library

Pdh.lib

DLL

Pdh.dll

See also

PdhOpenLog
PdhVbGetLogFileSize
PdhVbUpdateLog

 

 

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