ISLOWER(3P)

💖 ISLOWER(3P) 💖

okay bestie, welcome to the POSIX Programmer's Manual entry for islower, islower_l — yes that's the whole manual name, it's giving official, it's giving standards-body, we love her 💅

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✨ PROLOG ✨

so like, real talk first: this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux. no cap, that's the actual disclaimer, don't come for me 🙈

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🎀 NAME 🎀

islower, islower_l — test for a lowercase letter. that's it, that's the job, and she does it flawlessly ✨

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🦋 SYNOPSIS 🦋

#include <ctype.h>

int islower(int c);
int islower_l(int c, locale_t locale);

look at her. two little functions. iconic. 👑

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🌸 DESCRIPTION 🌸

For islower(): 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. This volume of POSIX.1‐2017 defers to the ISO C standard. (basically the ISO C girlies are the final say, we're just respectfully agreeing 💜)

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

The c argument is an int, the value of which 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.

🚨 okay so this is the part where you listen. you feed her something that isn't an unsigned char-representable value and isn't EOF? undefined behavior. that's not a vibe. that's a jump scare. do NOT do that. 💀

The behavior is undefined if the locale argument to islower_l() is the special locale object LC_GLOBAL_LOCALE or is not a valid locale object handle.

😭 yeah, again. LC_GLOBAL_LOCALE? not a valid locale object handle? undefined. she said what she said.

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⭐ RETURN VALUE ⭐

The islower() and islower_l() functions shall return non-zero if c is a lowercase letter; otherwise, they shall return 0. simple. binary. slay. 🫶

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💀 ERRORS 💀

No errors are defined.

The following sections are informative. (translation: the spicy main-character requirements are done, everything from here is bonus content 🎀)

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🌈 EXAMPLES 🌈

🍓 Testing for a Lowercase Letter

Two examples follow, the first using islower(), the second using multiple concurrent locales and islower_l(). bestie said "let me show you both ways" and honestly? obsessed. 💖

The examples test whether the value is a lowercase letter, based on the current locale, then use it as part of a key value.

/* Example 1 -- using islower() */
#include <ctype.h>
#include <stdlib.h>
#include <locale.h>
...
char *keystr;
int elementlen, len;
unsigned char c;
...
setlocale(LC_ALL, "");
...
len = 0;
while (len < elementlen) {
    c = (unsigned char) (rand() % 256);
...
    if (islower(c))
        keystr[len++] = c;
    }
...

/* Example 2 -- using islower_l() */
#include <ctype.h>
#include <stdlib.h>
#include <locale.h>
...
char *keystr;
int elementlen, len;
unsigned char c;
...
locale_t loc = newlocale (LC_ALL_MASK, "", (locale_t) 0);
...
len = 0;
while (len < elementlen) {
    c = (unsigned char) (rand() % 256);
...
    if (islower_l(c, loc))
        keystr[len++] = c;
    }
...

two whole examples, both gorgeous, both copied character-for-character because that's the rules 💅

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🧚 APPLICATION USAGE 🧚

To ensure applications portability, especially across natural languages, only these functions and the functions in the reference pages listed in the SEE ALSO section should be used for character classification. fr fr, if you want your code to travel the world, stick to the certified list. ✈️🌍

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🎀 RATIONALE 🎀

None.

(she's mysterious. she's minimal. she's giving nothing and everything at the same time 😌)

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🦋 FUTURE DIRECTIONS 🦋

None.

(no plans, no drama, just vibes 🌸)

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👑 SEE ALSO 👑

isalnum(), isalpha(), isblank(), iscntrl(), isdigit(), isgraph(), isprint(), ispunct(), isspace(), isupper(), isxdigit(), setlocale(), uselocale()

The Base Definitions volume of POSIX.1‐2017, Chapter 7, Locale, <ctype.h>, <locale.h>

the whole ctype squad, assembled. it's giving family reunion 🫶✨

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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. 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 .

🙈 ngl if you spot a typo it's probably from the man page conversion pipeline, not from the original standard girlies. report it at that link, they'll handle it. 💅

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and that's the whole page, bestie!! 🎉 this absolute banger of a manual page is brought to you by IEEE and The Open Group, dated 2017 — IEEE/The Open Group 2017 ISLOWER(3P) — mwah, periodt. 💖✨🦋