tail head cat sleep
QR code linking to this page

Manual Pages  — ISALPHA


isalpha – alphabetic character test



Standard C Library (libc, -lc)


#include <ctype.h>

isalpha(int c);

isalpha_l(int c, locale_t loc);


The isalpha() function tests for any character for which isupper(3) or islower(3) is true. 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):

amp;101 ``A''
102 ``B'' 103 ``C'' 104 ``D'' 105 ``E''

amp;106 ``F''
107 ``G'' 110 ``H'' 111 ``I'' 112 ``J''

amp;113 ``K''
114 ``L'' 115 ``M'' 116 ``N'' 117 ``O''

amp;120 ``P''
121 ``Q'' 122 ``R'' 123 ``S'' 124 ``T''

amp;125 ``U''
126 ``V'' 127 ``W'' 130 ``X'' 131 ``Y''

amp;132 ``Z''
141 ``a'' 142 ``b'' 143 ``c'' 144 ``d''

amp;145 ``e''
146 ``f'' 147 ``g'' 150 ``h'' 151 ``i''

amp;152 ``j''
153 ``k'' 154 ``l'' 155 ``m'' 156 ``n''

amp;157 ``o''
160 ``p'' 161 ``q'' 162 ``r'' 163 ``s''

amp;164 ``t''
165 ``u'' 166 ``v'' 167 ``w'' 170 ``x''

amp;171 ``y''
172 ``z'' amp; amp; amp;

The isalpha_l() function takes an explicit locale argument, whereas the isalpha() function uses the current global or per-thread locale.


The isalpha() function returns zero if the character tests false and returns non-zero if the character tests true.


The BSD 4.4 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 iswalpha() function should be used instead.


ctype(3), islower(3), isupper(3), iswalpha(3), xlocale(3), ascii(7)


The isalpha() function conforms to ISO/IEC 9899:1990 ("ISO C90"). The isalpha_l() function conforms to IEEE Std 1003.1-2008 ("POSIX.1").

ISALPHA (3) July 17, 2005

tail head cat sleep
QR code linking to this page

Please direct any comments about this manual page service to Ben Bullock. Privacy policy.

The number of UNIX installations has grown to 10, with more expected.
— UNIX Programming Manual, 1972