isalpha
Defined in header <ctype.h>
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Checks if the given character is an alphabetic character, i.e. either an uppercase letter (ABCDEFGHIJKLMNOPQRSTUVWXYZ
), or a lowercase letter (abcdefghijklmnopqrstuvwxyz
).
In locales other than "C"
, an alphabetic character is a character for which isupper()
or islower()
returns true
or any other character considered alphabetic by the locale. In any case, iscntrl()
, isdigit()
, ispunct()
and isspace()
will return false
for this character.
The behavior is undefined if the value of ch
is not representable as unsigned char
or is not equal to EOF
.
Parameters
ch | - | character to classify |
Return value
Non-zero value if the character is an alphabetic character, zero otherwise.
Example
Demonstrates the use of isalpha() with different locales (OS-specific).
#include <ctype.h>
#include <stdio.h>
#include <locale.h>
int main(void)
{
unsigned char c = '\xdf'; // German letter ß in ISO-8859-1
printf("isalpha('\\xdf') in default C locale returned %d\n", !!isalpha(c));
setlocale(LC_CTYPE, "de_DE.iso88591");
printf("isalpha('\\xdf') in ISO-8859-1 locale returned %d\n", !!isalpha(c));
}
Output:
isalpha('\xdf') in default C locale returned 0
isalpha('\xdf') in ISO-8859-1 locale returned 1
References
C11 standard (ISO/IEC 9899:2011):
- 7.4.1.2 The isalpha function (p: 200-201)
C99 standard (ISO/IEC 9899:1999):
- 7.4.1.2 The isalpha function (p: 181-182)
C89/C90 standard (ISO/IEC 9899:1990):
- 4.3.1.2 The isalpha function
See also
(C95) |
checks if a wide character is alphabetic (function) |
ASCII values | characters | iscntrl |
isprint |
isspace |
isblank |
isgraph |
ispunct |
isalnum |
isalpha |
isupper |
islower |
isdigit |
isxdigit | ||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
decimal | hexadecimal | octal | |||||||||||||
0–8 | \x0 –\x8
|
\0 –\10
|
control codes (NUL , etc.)
|
≠0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
9 | \x9
|
\11
|
tab (\t )
|
≠0
|
0
|
≠0
|
≠0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
10–13 | \xA –\xD
|
\12 –\15
|
whitespaces (\n , \v , \f , \r )
|
≠0
|
0
|
≠0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
14–31 | \xE –\x1F
|
\16 –\37
|
control codes | ≠0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
32 | \x20
|
\40
|
space | 0
|
≠0
|
≠0
|
≠0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
33–47 | \x21 –\x2F
|
\41 –\57
|
!"#$%&'()*+,-./
|
0
|
≠0
|
0
|
0
|
≠0
|
≠0
|
0
|
0
|
0
|
0
|
0
|
0
|
48–57 | \x30 –\x39
|
\60 –\71
|
0123456789
|
0
|
≠0
|
0
|
0
|
≠0
|
0
|
≠0
|
0
|
0
|
0
|
≠0
|
≠0
|
58–64 | \x3A –\x40
|
\72 –\100
|
:;<=>?@
|
0
|
≠0
|
0
|
0
|
≠0
|
≠0
|
0
|
0
|
0
|
0
|
0
|
0
|
65–70 | \x41 –\x46
|
\101 –\106
|
ABCDEF
|
0
|
≠0
|
0
|
0
|
≠0
|
0
|
≠0
|
≠0
|
≠0
|
0
|
0
|
≠0
|
71–90 | \x47 –\x5A
|
\107 –\132
|
GHIJKLMNOP
|
0
|
≠0
|
0
|
0
|
≠0
|
0
|
≠0
|
≠0
|
≠0
|
0
|
0
|
0
|
91–96 | \x5B –\x60
|
\133 –\140
|
[\]^_`
|
0
|
≠0
|
0
|
0
|
≠0
|
≠0
|
0
|
0
|
0
|
0
|
0
|
0
|
97–102 | \x61 –\x66
|
\141 –\146
|
abcdef
|
0
|
≠0
|
0
|
0
|
≠0
|
0
|
≠0
|
≠0
|
0
|
≠0
|
0
|
≠0
|
103–122 | \x67 –\x7A
|
\147 –\172
|
ghijklmnop
|
0
|
≠0
|
0
|
0
|
≠0
|
0
|
≠0
|
≠0
|
0
|
≠0
|
0
|
0
|
123–126 | \x7B –\x7E
|
\172 –\176
|
}~ | 0
|
≠0
|
0
|
0
|
≠0
|
≠0
|
0
|
0
|
0
|
0
|
0
|
0
|
127 | \x7F
|
\177
|
backspace character (DEL )
|
≠0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
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