ISUPPER(3POSIX)

💖 ISUPPER(3POSIX) — the POSIX Programmer's Manual, but make it make sense 💖

okay bestie, welcome to the ISUPPER(3POSIX) page of the POSIX Programmer's Manual. yes you're literally in the right place, sit down, hydrate, let's go 🫶

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✨ PROLOG ✨

okay so first things first, a little disclaimer moment because the grown-ups made us say it:

this manual page is part of the POSIX Programmer's Manual. the Linux implementation of this interface may differ (so like… consult the corresponding Linux manual page for the deets on Linux behavior), or honestly the interface may not be implemented on Linux at all. not every baddie makes it to every platform, iykyk 💅

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🌸 NAME 🌸

isupper, isupper_l — test for an uppercase letter

like. that's it. that's the whole job. is it uppercase? yes or no. iconic honestly.

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🦋 SYNOPSIS 🦋

#include <ctype.h>

int isupper(int c);
int isupper_l(int c, locale_t locale);

look at those two little functions, so small, so powerful ✨

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💜 DESCRIPTION 💜

okay so for isupper() specifically: the functionality described on this reference page is aligned with the ISO C standard. and like, 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.

the isupper() and isupper_l() functions shall test whether c is a character of class upper in the current locale, or in the locale represented by locale, respectively; see the Base Definitions volume of POSIX.1‐2017, Chapter 7, Locale.

now, the c argument is an int, and the value of it — the application shall ensure — is a character representable as an unsigned char or equal to the value of the macro EOF. if the argument has any other value, the behavior is undefined. 🫣 so like, don't do that. please.

bestie warning 🚨 the behavior is undefined if the locale argument to isupper_l() is the special locale object LC_GLOBAL_LOCALE or is not a valid locale object handle. no cap.

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👑 RETURN VALUE 👑

the isupper() and isupper_l() functions shall return non-zero if c is an uppercase letter; otherwise, they shall return 0.

so: truthy = yes uppercase. zero = nope. simple as that, periodt 💅

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🌈 ERRORS 🌈

No errors are defined.

which is honestly such a chill life. the following sections are informative, so like, they're the vibe notes, not the law 📝

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🍓 EXAMPLES 🍓

None.

yeah. none. the well is dry, bestie. moving on 💀

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🎀 APPLICATION USAGE 🎀

to ensure applications portability — especially across natural languages, which is a whole thing — only these functions and the functions in the reference pages listed in the SEE ALSO section should be used for character classification. that's the assignment. stay in your lane, it's a cute lane 🧚

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⭐ RATIONALE ⭐

None.

nothing to explain, it simply is. main character energy ✨

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🔥 FUTURE DIRECTIONS 🔥

None.

the future is… unchanged. slay.

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💖 SEE ALSO 💖

go read these too, they're all in the same friend group:

• isalnum()
• isalpha()
• isblank()
• iscntrl()
• isdigit()
• isgraph()
• islower()
• isprint()
• ispunct()
• isspace()
• isxdigit()
• setlocale()
• uselocale()

and also, from the Base Definitions volume of POSIX.1‐2017:

• Chapter 7, Locale
• <ctype.h>
• <locale.h>

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💌 COPYRIGHT 💌

okay legal moment, stay with me, this part matters:

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. 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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okay that's the whole page, you ate that reading, so proud 🥹

this has been brought to you by IEEE/The Open Group, 2017, on the page ISUPPER(3POSIX) — stay uppercase, stay iconic, mwah 💅💖🦋