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Difference between revisions of "cpp/string/byte/isalpha"

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< cpp‎ | string‎ | byte
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In locales other than {{c|"C"}}, an alphabetic character is a character for which {{lc|std::isupper()}} or {{lc|std::islower()}} returns non-zero or any other character considered alphabetic by the locale. In any case, {{lc|std::iscntrl()}}, {{lc|std::isdigit()}}, {{lc|std::ispunct()}} and {{lc|std::isspace()}} will return zero for this character.
 
In locales other than {{c|"C"}}, an alphabetic character is a character for which {{lc|std::isupper()}} or {{lc|std::islower()}} returns non-zero or any other character considered alphabetic by the locale. In any case, {{lc|std::iscntrl()}}, {{lc|std::isdigit()}}, {{lc|std::ispunct()}} and {{lc|std::isspace()}} will return zero for this character.
  
−
The behavior is undefined if the value of {{tt|ch}} is not representable as {{c|unsigned char}} and is not equal to {{c|EOF}}.
+
The behavior is undefined if the value of {{tt|ch}} is not representable as {{c|unsigned char}} or is not equal to {{c|EOF}}.
  
 
===Parameters===
 
===Parameters===

Revision as of 05:49, 2 February 2017

 
C++
 
Strings library
 
Null-terminated byte strings
Functions
Character manipulation
isalpha
(C++11)    
Conversions to numeric formats
(C++11)
(C++11)(C++11)
(C++11)(C++11)
String manipulation
String examination
Memory manipulation
Miscellaneous
 
Defined in header <cctype>
int isalpha( int ch );

Checks if the given character is an alphabetic character as classified by the currently installed C locale. In the default locale, the following characters are alphabetic:

  • uppercase letters ABCDEFGHIJKLMNOPQRSTUVWXYZ
  • lowercase letters abcdefghijklmnopqrstuvwxyz

In locales other than "C", an alphabetic character is a character for which std::isupper() or std::islower() returns non-zero or any other character considered alphabetic by the locale. In any case, std::iscntrl(), std::isdigit(), std::ispunct() and std::isspace() will return zero for this character.

The behavior is undefined if the value of ch is not representable as unsigned char or is not equal to EOF.

Contents

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).

Run this code
#include <iostream>
#include <cctype> 
#include <clocale>
 
int main()
{        
    unsigned char c = '\xdf'; // German letter ß in ISO-8859-1
 
    std::cout << "isalpha(\'\\xdf\', default C locale) returned "
               << std::boolalpha << (bool)std::isalpha(c) << '\n';
 
    std::setlocale(LC_ALL, "de_DE.iso88591");
    std::cout << "isalpha(\'\\xdf\', ISO-8859-1 locale) returned "
              << std::boolalpha << (bool)std::isalpha(c) << '\n';
 
}

Output: 

isalpha('\xdf', default C locale) returned false
isalpha('\xdf', ISO-8859-1 locale) returned true

See also

 checks if a character is classified as alphabetic by a locale
(function template) [edit]
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–\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
QRSTUVWXYZ 		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
qrstuvwxyz 		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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