CLOCK(3POSIX)

🌸 CLOCK(3POSIX) — ok bestie, let's talk CPU time 💖

So this little cutie lives in the POSIX Programmer's Manual, and the page is literally called CLOCK(3POSIX). She's giving "how much processor time have I eaten" energy, and honestly? Iconic.

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⚠️ PROLOG (the fine print, but make it cute)

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ — so bestie, if you're on Linux, go consult the corresponding Linux manual page for the deets on Linux behavior. Or… the interface might not even be implemented on Linux at all. 😭 It's giving "check first, assume nothing".

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✨ NAME ✨

clock — report CPU time used 🕰️

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🎀 SYNOPSIS 🎀

#include <time.h>

clock_t clock(void);

That's it. No args. She takes nothing and gives you a clock_t. Simple. Elegant. Slay.

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💅 DESCRIPTION 💅

The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional — no drama intended, fr fr. This volume of POSIX.1‐2017 defers to the ISO C standard. Periodt.

The clock() function shall return the implementation's best approximation to the processor time used by the process since the beginning of an implementation-defined era related only to the process invocation. So like… it's measuring your process, not the whole system. Main character energy only. 👑

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🔥 RETURN VALUE 🔥

Wanna know the time in seconds? Bestie, you gotta divide the value returned by clock() by the value of the macro CLOCKS_PER_SEC. That's the move. 💫

CLOCKS_PER_SEC is defined to be one million in <time.h>. One million! That's a lot of ticks. 💀

And if the processor time used is not available, or its value cannot be represented? The function shall return the value (clock_t)-1. That's the "nope, can't do it" answer. 🙈

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😭 ERRORS 😭

No errors are defined. None. Zero. Not a single one. She doesn't do errors, she does vibes. ✨

The following sections are informative. (So like, chill reading, not rules-rules.)

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🦋 EXAMPLES 🦋

None. 💀 Nothing. Empty. The girlies gave us zero examples. We move.

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🌈 APPLICATION USAGE 🌈

Okay this part is lowkey important, listen up:

In programming environments where clock_t is a 32-bit integer type and CLOCKS_PER_SEC is one million, clock() will start failing in less than 36 minutes of processor time for signed clock_t, or 72 minutes for unsigned clock_t. Not hours. Minutes. The math is not mathing and that's just how it is. 😭

Applications intended to be portable to such environments should use times() instead — or clock_gettime() with CLOCK_PROCESS_CPUTIME_ID, if supported. Upgrade your tools, bestie. 🫶

In order to measure the time spent in a program, clock() should be called at the start of the program and its return value subtracted from the value returned by subsequent calls. Snapshot first, math later. 📸

The value returned by clock() is defined for compatibility across systems that have clocks with different resolutions. The resolution on any particular system need not be to microsecond accuracy. So don't come for her about precision, she's doing her best. 💅

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🧚 RATIONALE 🧚

None. The reasoning is simply not documented here. We accept that and we thrive. ✨

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⭐ FUTURE DIRECTIONS ⭐

None. The future is unspecified and honestly? That's a vibe.

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👑 SEE ALSO 👑

Go read these too, they're all in the girlie universe together:

• asctime()
• clock_getres()
• ctime()
• difftime()
• gmtime()
• localtime()
• mktime()
• strftime()
• strptime()
• time()
• times()
• utime()

The Base Definitions volume of POSIX.1‐2017, <time.h>

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📜 COPYRIGHT 📜

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group.

In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. Like, the original is the final boss. Don't fight it.

The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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And that's the whole page, bestie. Brought to you by IEEE/The Open Group, dated 2017. 💖 Thanks for reading, go divide by CLOCKS_PER_SEC and stay hydrated. 🍓