tolowerl

tolowerl is a term sometimes used to refer to a locale-aware variant of the C standard library function tolower, but it is not a standardized or universally recognized name. The ISO C standard defines int tolower(int ch) in <ctype.h>, which converts a character to lowercase according to the current C locale. In practice, many systems provide a locale-specific variant named tolower_l (with an underscore and an explicit locale argument) rather than a function literally called tolowerl.

In POSIX-compliant systems and glibc, the proper locale-aware function is tolower_l, with the signature int tolower_l(int ch, locale_t locale). It maps the input character to its lowercase equivalent using the character classification and mapping data of the provided locale’s LC_CTYPE category. If ch is not representable as an unsigned char or is EOF, the function returns ch unchanged. Non-letter characters are generally returned unchanged as well.

Locale handling: a locale_t object represents a specific cultural locale. It is created via newlocale or duplocale and can be applied to a thread with uselocale or thread-local locale settings. This allows different parts of a program to use different locale rules for case conversion.

Portability and usage: tolowerl is not part of the standard C or C++ libraries, and code that references tolowerl may fail on platforms lacking such a symbol. In portable code, use tolower (with the current locale) or tolower_l where available, or use C++ facilities such as std::tolower with a std::locale.

See also: tolower, towlower, tolower_l, locale_t, newlocale, uselocale.