GetSystemTimeAdjustment function

Determines whether the system is applying periodic time adjustments to its time-of-day clock, and obtains the value and period of any such adjustments.

Syntax


BOOL WINAPI GetSystemTimeAdjustment(
  _Out_  PDWORD lpTimeAdjustment,
  _Out_  PDWORD lpTimeIncrement,
  _Out_  PBOOL lpTimeAdjustmentDisabled
);

Parameters

lpTimeAdjustment [out]

A pointer to a variable that the function sets to the number of lpTimeIncrement100-nanosecond units added to the time-of-day clock for every period of time which actually passes as counted by the system. This value only has meaning if lpTimeAdjustmentDisabled is FALSE.

lpTimeIncrement [out]

A pointer to a variable that the function sets to the interval in 100-nanosecond units at which the system will add lpTimeAdjustment to the time-of-day clock. This value only has meaning if lpTimeAdjustmentDisabled is FALSE.

lpTimeAdjustmentDisabled [out]

A pointer to a variable that the function sets to indicate whether periodic time adjustment is in effect.

A value of TRUE indicates that periodic time adjustment is disabled, and the system time-of-day clock advances at the normal rate. In this mode, the system may adjust the time of day using its own internal time synchronization mechanisms. These internal time synchronization mechanisms may cause the time-of-day clock to change during the normal course of the system operation, which can include noticeable jumps in time as deemed necessary by the system.

A value of FALSE indicates that periodic time adjustment is being used to adjust the time-of-day clock. For each lpTimeIncrement period of time that actually passes, lpTimeAdjustment will be added to the time of day. If the lpTimeAdjustment value is smaller than lpTimeIncrement, the system time-of-day clock will advance at a rate slower than normal. If the lpTimeAdjustment value is larger than lpTimeIncrement, the time-of-day clock will advance at a rate faster than normal. If lpTimeAdjustment equals lpTimeIncrement, the time-of-day clock will advance at its normal speed. The lpTimeAdjustment value can be set by calling SetSystemTimeAdjustment. The lpTimeIncrement value is fixed by the system upon start, and does not change during system operation. In this mode, the system will not interfere with the time adjustment scheme, and will not attempt to synchronize time of day on its own via other techniques.

Return value

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

The GetSystemTimeAdjustment and SetSystemTimeAdjustment functions can be used to support algorithms that want to synchronize the time-of-day clock, reported by GetSystemTime and GetLocalTime, with another time source by using a periodic time adjustment.

The GetSystemTimeAdjustment function lets a caller determine whether periodic time adjustment is enabled, and if it is, obtain the amount of each adjustment and the time between adjustments. The SetSystemTimeAdjustment function lets a caller enable or disable periodic time adjustment, and set the value of the adjusting increment.

Requirements

Minimum supported client

Windows 2000 Professional [desktop apps only]

Minimum supported server

Windows 2000 Server [desktop apps only]

Header

Winbase.h (include Windows.h)

Library

Kernel32.lib

DLL

Kernel32.dll

See also

GetLocalTime
GetSystemTime
SetSystemTimeAdjustment
System Time
Time Functions

 

 

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