nl_langinfo / rpmatch (3) - glibc

Split from the chapter glibc: Locales into the per-function layout; see the method page and the glibc ledger for coverage status.

Declaration and gates

#include <langinfo.h>

char *nl_langinfo(nl_item item);                       /* line 661 */
char *nl_langinfo_l(nl_item item, locale_t locale);    /* line 669 */

#include <stdlib.h>

int rpmatch(const char *response);                     /* line 1088 */

nl_langinfo is unconditional in /usr/include/langinfo.h; the _l twin needs _POSIX_C_SOURCE >= 200809L (nl_langinfo(3)). rpmatch sits in the __USE_MISC block of /usr/include/stdlib.h (line 1085-1089): _DEFAULT_SOURCE (glibc >= 2.19), formerly _SVID_SOURCE (rpmatch(3)).

Semantics

nl_langinfo is the “elegant” per-item locale query over localeconv’s single blob: given an nl_item such as CODESET, D_T_FMT, T_FMT, RADIXCHAR, YESEXPR/NOEXPR, CRNCYSTR, it returns the string the current global locale assigns to that element (nl_langinfo(3), manual node The Elegant and Fast Way). The returned pointer may be overwritten by later locale changes or calls, so copy anything to be kept. nl_langinfo_l queries an explicit locale object instead. rpmatch classifies a yes/no answer internationally: responses matching ^[Yy] are always affirmative (1), ^[Nn] always negative (0), anything else is matched against the locale’s YESEXPR/NOEXPR regular expressions from LC_MESSAGES (rpmatch(3)).

Gotchas and portability

• The return value points into locale storage: not a stable buffer, not owned by the caller (nl_langinfo(3)).
• rpmatch returns -1 for unrecognized answers – always handle it rather than treating nonzero as “yes”.
• rpmatch is a glibc/SVID extension: musl 1.2.5 has nl_langinfo (src/locale/langinfo.c) but no rpmatch (verified absence in include/stdlib.h and src/).

References

• glibc manual: locale.texi, nodes The Elegant and Fast Way, Yes-or-No Questions
• man3: nl_langinfo(3), rpmatch(3)
• headers: /usr/include/langinfo.h, /usr/include/stdlib.h
• musl: src/locale/langinfo.c