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ISLOWER(3) FreeBSD Library Functions Manual ISLOWER(3) NAME islower, islower_l - lower-case character test LIBRARY Standard C Library (libc, -lc) SYNOPSIS #include <ctype.h> int islower(int c); int islower_l(int c, locale_t loc); DESCRIPTION The islower() and islower_l() functions test for any lower-case letters. The value of the argument must be representable as an unsigned char or the value of EOF. In the ASCII character set, this includes the following characters (with their numeric values shown in octal): 141 ``a'' 142 ``b'' 143 ``c'' 144 ``d'' 145 ``e'' 146 ``f'' 147 ``g'' 150 ``h'' 151 ``i'' 152 ``j'' 153 ``k'' 154 ``l'' 155 ``m'' 156 ``n'' 157 ``o'' 160 ``p'' 161 ``q'' 162 ``r'' 163 ``s'' 164 ``t'' 165 ``u'' 166 ``v'' 167 ``w'' 170 ``x'' 171 ``y'' 172 ``z'' The islower_l() function takes an explicit locale argument, whereas the islower() function uses the current global or per-thread locale. RETURN VALUES The islower() and islower_l() functions return zero if the character tests false and return non-zero if the character tests true. COMPATIBILITY The 4.4BSD extension of accepting arguments outside of the range of the unsigned char type in locales with large character sets is considered obsolete and may not be supported in future releases. The iswlower() or iswlower_l() function should be used instead. SEE ALSO ctype(3), ctype_l(3), iswlower(3), iswlower_l(3), tolower(3), tolower_l(3), xlocale(3), ascii(7) STANDARDS The islower() function conforms to ISO/IEC 9899:1990 ("ISO C90"). The islower_l() function conforms to IEEE Std 1003.1-2008 ("POSIX.1"). HISTORY The islower() function first appeared in Version 7 AT&T UNIX. FreeBSD 14.1-RELEASE-p8 December 19, 2022 FreeBSD 14.1-RELEASE-p8