Tcl_GetTime(3) Tcl Library Procedures Tcl_GetTime(3)______________________________________________________________________________NAME
Tcl_GetTime, Tcl_SetTimeProc, Tcl_QueryTimeProc - get date and time
SYNOPSIS
#include <tcl.h>
Tcl_GetTime(timePtr)
Tcl_SetTimeProc(getProc, scaleProc, clientData)
Tcl_QueryTimeProc(getProcPtr, scaleProcPtr, clientDataPtr)
ARGUMENTS
Tcl_Time * timePtr (out) Points to memory in which to store the
date and time information.
Tcl_GetTimeProc * getProc (in) Pointer to handler function
replacing Tcl_GetTime's access
to the OS.
Tcl_ScaleTimeProc * scaleProc (in) Pointer to handler function
for the conversion of time
delays in the virtual
domain to real-time.
ClientData * clientData (in) Value passed through to the two
handler functions.
Tcl_GetTimeProc ** getProcPtr (inout) Pointer to place the cur‐
rently registered get han‐
dler function into.
Tcl_ScaleTimeProc ** scaleProcPtr (inout) Pointer to place the
currently registered
scale handler function
into.
ClientData ** clientDataPtr (inout) Pointer to place the cur‐
rently registered pass-
through value into.
_________________________________________________________________DESCRIPTION
The Tcl_GetTime function retrieves the current time as a Tcl_Time
structure in memory the caller provides. This structure has the fol‐
lowing definition:
typedef struct Tcl_Time {
long sec;
long usec;
} Tcl_Time;
On return, the sec member of the structure is filled in with the number
of seconds that have elapsed since the epoch: the epoch is the point in
time of 00:00 UTC, 1 January 1970. This number does not count leap
seconds - an interval of one day advances it by 86400 seconds regard‐
less of whether a leap second has been inserted.
The usec member of the structure is filled in with the number of
microseconds that have elapsed since the start of the second designated
by sec. The Tcl library makes every effort to keep this number as pre‐
cise as possible, subject to the limitations of the computer system.
On multiprocessor variants of Windows, this number may be limited to
the 10- or 20-ms granularity of the system clock. (On single-processor
Windows systems, the usec field is derived from a performance counter
and is highly precise.)
The Tcl_SetTime function registers two related handler functions with
the core. The first handler function is a replacement for Tcl_GetTime,
or rather the OS access made by Tcl_GetTime. The other handler function
is used by the Tcl notifier to convert wait/block times from the vir‐
tual domain into real time.
The Tcl_QueryTime function returns the currently registered handler
functions. If no external handlers were set then this will return the
standard handlers accessing and processing the native time of the OS.
The arguments to the function are allowed to be NULL; and any argument
which is NULL is ignored and not set.
Any handler pair specified has to return data which is consistent
between them. In other words, setting one handler of the pair to some‐
thing assuming a 10-times slowdown, and the other handler of the pair
to something assuming a two-times slowdown is wrong and not allowed.
The set handler functions are allowed to run the delivered time back‐
wards, however this should be avoided. We have to allow it as the
native time can run backwards as the user can fiddle with the system
time one way or other. Note that the insertion of the hooks will not
change the behaviour of the Tcl core with regard to this situation,
i.e. the existing behaviour is retained.
SEE ALSO
clock
KEYWORDS
date, time
Tcl 8.4 Tcl_GetTime(3)
