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Manual Pages  — ISALNUM


isalnum – alphanumeric character test



Standard C Library (libc, -lc)


#include <ctype.h>

isalnum(int c);

isalnum_l(int c, locale_t loc);


The isalnum() function tests for any character for which isalpha(3) or isdigit(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;060 ``0''
061 ``1'' 062 ``2'' 063 ``3'' 064 ``4''

amp;065 ``5''
066 ``6'' 067 ``7'' 070 ``8'' 071 ``9''

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 isalnum_l() function takes an explicit locale argument, whereas the isalnum() function uses the current global or per-thread locale.


The isalnum() 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 iswalnum() function should be used instead.


ctype(3), isalpha(3), isdigit(3), iswalnum(3), xlocale(3), ascii(7)


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

ISALNUM (3) July 17, 2005

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