QueryTraceW function (evntrace.h)

The QueryTrace function retrieves the property settings and session statistics for the specified event tracing session.

The ControlTrace function supersedes this function.


  TRACEHANDLE             TraceHandle,
  LPCWSTR                 InstanceName,



Handle to the event tracing session for whose properties and statistics you want to query, or NULL. You must specify SessionHandle if SessionName is NULL. However, ETW ignores the handle if SessionName is not NULL. The handle is returned by the StartTrace function.


Pointer to a null-terminated string that specifies the name of the event tracing session whose properties and statistics you want to query, or NULL. You must specify SessionName if SessionHandle is NULL.

To specify the NT Kernel Logger session, set SessionName to KERNEL_LOGGER_NAME.


Pointer to an initialized EVENT_TRACE_PROPERTIES structure.

You only need to set the Wnode.BufferSize member of the EVENT_TRACE_PROPERTIES structure. You can use the maximum session name (1024 characters) and maximum log file name (1024 characters) lengths to calculate the buffer size and offsets if not known.

On output, the structure members contain the property settings and session statistics for the event tracing session.

Starting with Windows 10, version 1703:  For better performance in cross process scenarios, you can now pass filtering in to QueryTrace for system wide private loggers. You will need to pass in the new EVENT_TRACE_PROPERTIES_V2 structure to include filtering information. See Configuring and Starting a Private Logger Session for more details.

Return value

If the function succeeds, the return value is ERROR_SUCCESS.

If the function fails, the return value is one of the system error codes. The following table includes some common errors and their causes.

Return code Description
One of the following is true:
  • The Wnode.BufferSize member of Properties specifies an incorrect size.
  • Properties does not have sufficient space allocated to hold a copy of the session name and log file name (if used).
One of the following is true:
  • Properties is NULL.
  • SessionName and SessionHandle are both NULL.
Only users running with elevated administrative privileges, users in the Performance Log Users group, and services running as LocalSystem, LocalService, NetworkService can query event tracing sessions. To grant a restricted user the ability to query trace sessions, add them to the Performance Log Users group or see EventAccessControl.

Windows XP and Windows 2000:  Anyone can control a trace session.

The given session is not running.


Controllers call this function.

To update the property settings and session statistics for an event tracing session, call the UpdateTrace function.


The evntrace.h header defines QueryTrace 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.


Minimum supported client Windows 2000 Professional [desktop apps | UWP apps]
Minimum supported server Windows 2000 Server [desktop apps | UWP apps]
Target Platform Windows
Header evntrace.h
Library Advapi32.lib
DLL Advapi32.dll

See also