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isalpha

From cppreference.com
< c‎ | string‎ | byte
 
 
 
Null-terminated byte strings
Functions
Character manipulation
Conversions to and from numeric formats
(C23)(C23)(C23)
String manipulation String examination Memory manipulation Miscellaneous
 
Defined in header <ctype.h>
int isalpha( int ch );

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 and is not equal to EOF .

Contents

[edit] Parameters

ch - character to classify

[edit] Return value

Non-zero value if the character is an alphabetic character, zero otherwise.

[edit] Example

Demonstrates the use of isalpha with different locales (OS-specific).

Run this code
#include <ctype.h>
#include <locale.h>
#include <stdio.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));
}

Possible output: 

isalpha('\xdf') in default C locale returned 0
isalpha('\xdf') in ISO-8859-1 locale returned 1

[edit] References

  • C23 standard (ISO/IEC 9899:2024):
  • 7.4.1.2 The isalpha function (p: TBD)
  • C17 standard (ISO/IEC 9899:2018):
  • 7.4.1.2 The isalpha function (p: 145)
  • 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

[edit] See also

(C95)
checks if a wide character is alphabetic
(function) [edit]
C++ documentation for isalpha
ASCII values characters

iscntrl
iswcntrl

isprint
iswprint

isspace
iswspace

isblank
iswblank

isgraph
iswgraph

ispunct
iswpunct

isalnum
iswalnum

isalpha
iswalpha

isupper
iswupper

islower
iswlower

isdigit
iswdigit

isxdigit
iswxdigit

decimal hexadecimal octal
0–8 \x0–\x8 0円–10円 control codes (NUL, etc.) ≠0 0 0 0 0 0 0 0 0 0 0 0
9 \x9 11円 tab (\t) ≠0 0 ≠0 ≠0 0 0 0 0 0 0 0 0
10–13 \xA–\xD 12円–15円 whitespaces (\n, \v, \f, \r) ≠0 0 ≠0 0 0 0 0 0 0 0 0 0
14–31 \xE–\x1F 16円–37円 control codes ≠0 0 0 0 0 0 0 0 0 0 0 0
32 \x20 40円 space 0 ≠0 ≠0 ≠0 0 0 0 0 0 0 0 0
33–47 \x21–\x2F 41円–57円 !"#$%&'()*+,-./ 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
48–57 \x30–\x39 60円–71円 0123456789 0 ≠0 0 0 ≠0 0 ≠0 0 0 0 ≠0 ≠0
58–64 \x3A–\x40 72円–100円 :;<=>?@ 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
65–70 \x41–\x46 101円–106円 ABCDEF 0 ≠0 0 0 ≠0 0 ≠0 ≠0 ≠0 0 0 ≠0
71–90 \x47–\x5A 107円–132円 GHIJKLMNOP
QRSTUVWXYZ 		0 ≠0 0 0 ≠0 0 ≠0 ≠0 ≠0 0 0 0
91–96 \x5B–\x60 133円–140円 [\]^_` 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
97–102 \x61–\x66 141円–146円 abcdef 0 ≠0 0 0 ≠0 0 ≠0 ≠0 0 ≠0 0 ≠0
103–122 \x67–\x7A 147円–172円 ghijklmnop
qrstuvwxyz 		0 ≠0 0 0 ≠0 0 ≠0 ≠0 0 ≠0 0 0
123–126 \x7B–\x7E 173円–176円 {|}~ 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
127 \x7F 177円 backspace character (DEL) ≠0 0 0 0 0 0 0 0 0 0 0 0

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