NL_LANGINFO(3P)

💖 NL_LANGINFO — bestie, it's the language info page 💖

okay so real talk: this one lives in the POSIX Programmer's Manual. Heads up tho — the Linux implementation of this interface may differ, so if you're on Linux, go read the matching Linux manual page for the actual tea. Or, plot twist, the interface might not even be implemented on Linux at all. 🙈

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✨ NAME ✨

nl_langinfo, nl_langinfo_l — language information 🗣️💬

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🌸 SYNOPSIS 🌸

#include <langinfo.h>

char *nl_langinfo(nl_item item);
char *nl_langinfo_l(nl_item item, locale_t locale);

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🦋 DESCRIPTION 🦋

So basically, nl_langinfo() and nl_langinfo_l() hand you back a pointer to a string full of info about whatever language or cultural area is defined in your current locale — or, for nl_langinfo_l(), in the locale that locale represents (peep <langinfo.h> for the deets). The manifest constant names and values of item are also defined in <langinfo.h>. 💅

Like, for example:

nl_langinfo(ABDAY_1)

would return a pointer to the string "Dom" if the identified language was Portuguese, and "Sun" if the identified language was English. Slay.

nl_langinfo_l(ABDAY_1, loc)

would return a pointer to the string "Dom" if the identified language of the locale represented by loc was Portuguese, and "Sun" if the identified language of the locale represented by loc was English. Same energy, different locale. ✨

Now the important bits: nl_langinfo() need not be thread-safe. Not me warning you. 🫶

And it's undefined behavior if the locale argument to nl_langinfo_l() is the special locale object LC_GLOBAL_LOCALE, or if it's not a valid locale object handle. Like, do not do that. 💀

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👑 RETURN VALUE 👑

In a locale where langinfo data is not defined, these functions shall return a pointer to the corresponding string in the POSIX locale. In all locales, these functions shall return a pointer to an empty string if item contains an invalid setting.

The application shall not modify the string returned. 🚫 Don't touch it, bestie.

The pointer returned by nl_langinfo() might be invalidated, or the string content might be overwritten, by:

• a subsequent call to nl_langinfo() in any thread
• a subsequent call to nl_langinfo_l() in the same thread or the initial thread
• subsequent calls to setlocale() with a category corresponding to the category of item (see <langinfo.h>) or the category LC_ALL
• subsequent calls to uselocale() which change the category corresponding to the category of item

The pointer returned by nl_langinfo_l() might be invalidated, or the string content might be overwritten, by:

• a subsequent call to nl_langinfo_l() in the same thread
• a subsequent call to nl_langinfo() in any thread
• subsequent calls to freelocale() or newlocale() which free or modify the locale object that was passed to nl_langinfo_l()

The returned pointer and the string content might also be invalidated if the calling thread is terminated. 😭 it's fragile, we know.

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💀 ERRORS 💀

No errors are defined.

The following sections are informative.

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🎀 EXAMPLES 🎀

🌈 Getting Date and Time Formatting Information 🌈

The following example returns a pointer to a string containing date and time formatting information, as defined in the LC_TIME category of the current locale.

#include <time.h>
#include <langinfo.h>
...
strftime(datestring, sizeof(datestring), nl_langinfo(D_T_FMT), tm);
...

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🍓 APPLICATION USAGE 🍓

The array pointed to by the return value should not be modified by the program, but may be modified by further calls to these functions. Lowkey just leave it alone and re-fetch if you need it again. 🙈

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🧚 RATIONALE 🧚

The possible interactions between internal data used by nl_langinfo() and nl_langinfo_l() are complicated by the fact that nl_langinfo_l() must be thread-safe but nl_langinfo() need not be. The various implementation choices are:

1. nl_langinfo_l() and nl_langinfo() use separate buffers, or at least one of them does not use an internal string buffer. In this case there are no interactions.
2. nl_langinfo_l() and nl_langinfo() share an internal per-thread buffer. There can be interactions, but only in the same thread.
3. nl_langinfo_l() uses an internal per-thread buffer, and nl_langinfo() uses (in all threads) the same buffer that nl_langinfo_l() uses in the initial thread. There can be interactions, but only when nl_langinfo_l() is called in the initial thread.

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⭐ FUTURE DIRECTIONS ⭐

None.

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🔥 SEE ALSO 🔥

• setlocale()
• uselocale()

The Base Definitions volume of POSIX.1‐2017, Chapter 7, Locale, <langinfo.h>, <locale.h>, <nl_types.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. 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 💅 this was IEEE/The Open Group, 2017, NL_LANGINFO(3P) — bye bestie, go read your locale data responsibly 🫶✨