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.\" Copyright (c) 2017 Ingo Schwarze <schwarze@openbsd.org>
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.Dd $Mdocdate: September 5 2017 $
.Dt ISALPHA 3
.Os
.Sh NAME
.Nm isalpha ,
.Nm isalpha_l
.Nd alphabetic single-byte character test
.Sh SYNOPSIS
.In ctype.h
.Ft int
.Fn isalpha "int c"
.Ft int
.Fn isalpha_l "int c" "locale_t locale"
.Sh DESCRIPTION
The
.Fn isalpha
and
.Fn isalpha_l
functions test whether
.Fa c
represents a letter.
.Pp
In the C locale, the complete list of alphabetic characters
is A\(enZ and a\(enz.
.Ox
always uses the C locale for these functions,
ignoring the global locale, the thread-specific locale, and the
.Fa locale
argument.
.Sh RETURN VALUES
These functions return zero if the character tests false or
non-zero if the character tests true.
.Sh ENVIRONMENT
On systems supporting non-ASCII single-byte character encodings,
these functions may return non-zero for additional characters,
and the results of
.Fn isalnum
may depend on the
.Ev LC_CTYPE
.Xr locale 1 ,
but they never return non-zero for any character for which
.Xr iscntrl 3 ,
.Xr isdigit 3 ,
.Xr ispunct 3 ,
or
.Xr isspace 3
is true.
.Sh SEE ALSO
.Xr isalnum 3 ,
.Xr isascii 3 ,
.Xr isblank 3 ,
.Xr iscntrl 3 ,
.Xr isdigit 3 ,
.Xr isgraph 3 ,
.Xr islower 3 ,
.Xr isprint 3 ,
.Xr ispunct 3 ,
.Xr isspace 3 ,
.Xr isupper 3 ,
.Xr iswalpha 3 ,
.Xr isxdigit 3 ,
.Xr stdio 3 ,
.Xr toascii 3 ,
.Xr tolower 3 ,
.Xr toupper 3 ,
.Xr ascii 7
.Sh STANDARDS
The
.Fn isalpha
function conforms to
.St -ansiC ,
and
.Fn isalpha_l
to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn isalpha
function first appeared in
.At v7 ,
and
.Fn isalpha_l
has been available since
.Ox 6.2 .
.Sh CAVEATS
The argument
.Fa c
must be
.Dv EOF
or representable as an
.Li unsigned char ;
otherwise, the result is undefined.