dysize(3)

💖 dysize(3) — it's giving calendar math, bestie 💖

okay so this one's from dysize(3) in the Library Functions Manual, and it is literally the shortest little cutie in the whole time-handling friend group. come sit, I'll tell you everything 💅

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✨ NAME ✨

dysize — get number of days for a given year 🗓️

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📚 LIBRARY 📚

Standard C library — that's libc, link it with -lc 🫶

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🌸 SYNOPSIS 🌸

#include <time.h>

int dysize(int year);

🎀 Feature Test Macro Requirements for glibc (see feature_test_macros(7)) 🎀

dysize():

• Since glibc 2.19:
  • _DEFAULT_SOURCE
• glibc 2.19 and earlier:
  • _BSD_SOURCE || _SVID_SOURCE

yes bestie, the era of your glibc genuinely changes which macro you gotta define. check your version, don't just guess 🙈

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🦋 DESCRIPTION 🦋

okay so here's the whole entire plot: the function hands you back 365 for a normal year and 366 for a leap year. that's it. that's the function. no cap, it's a one-trick pony and it ate 💅

the leap year math is based on this, verbatim:

(year) %4 == 0 && ((year) %100 != 0 || (year) %400 == 0)

and that exact same formula is defined in the macro __isleap(year), which you can also find chillin' in <time.h> ✨

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👑 ATTRIBUTES 👑

for an explanation of the terms used in this section, go peek at attributes(7) 📖

• Interface: dysize()
• Attribute: Thread safety
• Value: MT-Safe

so yeah, it's MT-Safe — you and your threads can all call it at once and nobody's gonna fight 🌈

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🧚 STANDARDS 🧚

None. as in: no standard claims this one. she's untethered. free-spirited. not in POSIX, not in ISO C, just vibing 😭

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💜 HISTORY 💜

• SunOS 4.x. — that's where she came from, ancient lore fr fr

and straight from the source, no paraphrasing: this is a compatibility function only. Don't use it in new programs.

bestie I'm so serious 😭 if you're writing something new, this is NOT the main character. keep it around for the old stuff and move on. periodt 💅

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🔥 SEE ALSO 🔥

• strftime(3)

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that's the whole page!! no more lore, she's tiny and she knows it 🎀

kisses, this was Linux man-pages 6.20, dated 2026-02-08 — and with that, dysize(3) is officially explained. slay, stay leap-year-aware, bye bestie 💖🦋✨