Tcl_GetTime(3)

💖 Tcl_GetTime — get date and time 💖

okay so bestie, this one lives in the Tcl Library Procedures section of the manual, and it's literally all about asking what time it is, and about being a lil sneaky and redefining what time it is. no cap. 🕰️✨

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✨ SYNOPSIS ✨

#include <tcl.h>

Tcl_GetTime(timePtr)

Tcl_SetTimeProc(getProc, scaleProc, clientData)

Tcl_QueryTimeProc(getProcPtr, scaleProcPtr, clientDataPtr)

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🎀 ARGUMENTS 🎀

• Tcl_Time *timePtr (out) — points at the memory where the date and time info gets stashed. it's your lil container, you bring it, we fill it 🫙
• Tcl_GetTimeProc getProc (in) — a pointer to the handler function that replaces the way Tcl_GetTime reaches out to the OS. like, we're ghosting the OS and letting your function answer instead 👻
• Tcl_ScaleTimeProc scaleProc (in) — a pointer to the handler function that converts time delays in the virtual domain into real-time. the translator bestie 🗣️
• void *clientData (in) — a value that just gets passed straight through to both of those handler functions. no thoughts, just vibes, it goes along for the ride 🚗
• Tcl_GetTimeProc *getProcPtr (out) — a pointer to the place where the currently registered get handler function gets dropped 📥
• Tcl_ScaleTimeProc *scaleProcPtr (out) — a pointer to the place where the currently registered scale handler function gets dropped 📥
• void **clientDataPtr (out) — a pointer to the place where the currently registered pass-through value gets dropped 📥

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🌸 DESCRIPTION 🌸

So Tcl_GetTime grabs the current time and hands it back to you as a Tcl_Time structure, living in memory you provided. she does not allocate, she does not surprise you, she just fills your lil box. iconic behavior honestly 💅

That structure is defined like this, exactly:

typedef struct {
    long long sec;
    long usec;
} Tcl_Time;

When it comes back to you, the sec member is holding the number of seconds that have elapsed since the epoch — and the epoch is that specific moment: 00:00 UTC, 1 January 1970. mark it in your calendar bestie, that's the birthday of all Unix time 🎂

and heads up: this number does not count leap seconds. one day advances it by exactly 86400 seconds, no matter whether a leap second got inserted or not. the math stays clean, the leap seconds get ignored, that's just the deal. ⏱️

The usec member gets filled in with the number of microseconds that have elapsed since the start of the second that sec points at. the Tcl library tries so hard to keep this number as precise as possible, subject to whatever the computer system can actually manage — she's doing her best, ok 😭

⚠️ real talk on precision: on multiprocessor variants of Windows, this number may be limited to the 10- or 20-ms granularity of the system clock. but on single-processor Windows systems, the usec field is derived from a performance counter and is highly precise. so it's giving... depends on your CPU count, lowkey.

🦋 VIRTUALIZED TIME 🦋

okay this is the main character section, the plot twist, the time-travel arc 🌈

Tcl_SetTimeProc registers two related handler functions with the core:

1. The first handler function is a replacement for Tcl_GetTime — or, more precisely, a replacement for the OS access that Tcl_GetTime makes. so it's not replacing the function itself, it's replacing the door she knocks on. big difference, iykyk 🚪
2. The other handler function is used by the Tcl notifier to convert wait/block times from the virtual domain into real time. so when something's like "wait 5 virtual seconds," this handler is the one doing the ✨math✨ to figure out how long that actually is.

Tcl_QueryTimeProc returns the handler functions that are currently registered. if no external handlers were ever set, this will return the standard handlers that access and process the native time of the OS — the defaults, the originals, the no-notes version 🍦

the arguments to this function are allowed to be NULL, and any argument which is NULL is simply ignored and not set. so you can ask for just one thing if you want, she won't be weird about it 🙈

The signatures of the handler functions go like this, verbatim:

typedef void Tcl_GetTimeProc(
        Tcl_Time *timebuf,
        void *clientData);
typedef void Tcl_ScaleTimeProc(
        Tcl_Time *timebuf,
        void *clientData);

The timebuf fields contain the time to manipulate, and the clientData fields contain a pointer that was supplied back when the handler functions got registered. it's the lil note you slipped them at signup 🫶

🔥 HARD RULE, NO EXCEPTIONS: any handler pair you specify has to return data that is consistent between them. in other words, setting one handler of the pair to something assuming a 10-times slowdown and the other handler of the pair to something assuming a two-times slowdown is wrong and not allowed. they have to agree. periodt. matching outfits or nothing, bestie 👯

The set handler functions are allowed to run the delivered time backwards — however, this should be avoided. we have to allow it because the native time can run backwards as the user can fiddle with the system time one way or other. so it's less "we endorse this" and more "we legally cannot stop the user from messing with the clock." noted! 🕳️

and also note: the insertion of the hooks will not change the behavior of the Tcl core with regard to this situation — i.e. the existing behavior is retained. so the vibes stay exactly the same, no surprise glow-up 💀

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👑 SEE ALSO 👑

• clock(n)

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🍓 KEYWORDS 🍓

date, time

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and that's the whole page, bestie!! this one came from the Tcl manual, version 8.4, and the page you just read is titled Tcl_GetTime(3) — go forth and get that time, and maybe virtualize it if you're feeling spicy 💜✨🦋