toupper(3) Library Functions Manual toupper(3) toupper, tolower, toupper_l, tolower_l - (libc -lc) #include int toupper(int c); int tolower(int c); int toupper_l(int c, locale_t locale); int tolower_l(int c, locale_t locale); glibc ( feature_test_macros(7)): toupper_l() tolower_l(): glibc 2.10: _XOPEN_SOURCE >= 700 glibc 2.10: _GNU_SOURCE . c toupper() . c. toupper_l() locale. c tolower() . c. tolower_l() locale. c unsigned char EOF . toupper_l() tolower_l() locale LC_GLOBAL_LOCALE ( duplocale(3)) . c . attributes(7). +------------+------------------------------------+--------------------+ || | | +------------+------------------------------------+--------------------+ |toupper()| | MT-Safe | |tolower()| | | |toupper_l()| | | |tolower_l() | | | +------------+------------------------------------+--------------------+ toupper() tolower() C11, POSIX.1-2008. toupper_l() tolower_l() POSIX.1-2008. toupper() tolower() C89 4.3BSD POSIX.1-2001. toupper_l() tolower_l() POSIX.1-2008. c EOF unsigned char. c char unsigned char : char c; ... res = toupper((unsigned char) c); char signed char int unsigned char. . "C" . sharp s . isalpha(3) newlocale(3) setlocale(3) towlower(3) towupper(3) uselocale(3) locale(7) 3 . . : . 6.18 8 2026 toupper(3)