From cppreference.com
intisalpha(intch);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 unsignedchar and is not equal to
.
Parameters
ch - character to classify Return value
Non-zero value if the character is an alphabetic character, zero otherwise.
Notes
Like all other functions from
, the behavior of std::isalpha is undefined if the argument's value is neither representable as unsignedchar nor equal to EOF. To use these functions safely with plain chars (or signedchars), the argument should first be converted to unsignedchar:
boolmy_isalpha(charch){returnstd::isalpha(static_cast<unsignedchar>(ch));}Similarly, they should not be directly used with standard algorithms when the iterator's value type is char or signedchar. Instead, convert the value to unsignedchar first:
intcount_alphas(conststd::string&s){returnstd::count_if(s.begin(),s.end(),// static_cast<int(*)(int)>(std::isalpha) // wrong// [](int c){ return std::isalpha(c); } // wrong// [](char c){ return std::isalpha(c); } // wrong[](unsignedcharc){returnstd::isalpha(c);}// correct);}Example
Demonstrates the use of std::isalpha with different locales (OS-specific).
Run this code
#include<cctype>#include<clocale>#include<iostream>intmain(){unsignedcharc='\xdf';// German letter ß in ISO-8859-1std::cout<<"isalpha(\'\\xdf\', default C locale) returned "<<std::boolalpha<<!!std::isalpha(c)<<'\n';std::setlocale(LC_ALL,"de_DE.iso88591");std::cout<<"isalpha(\'\\xdf\', ISO-8859-1 locale) returned "<<static_cast<bool>(std::isalpha(c))<<'\n';}Possible output:
isalpha('\xdf', default C locale) returned false isalpha('\xdf', ISO-8859-1 locale) returned true See also
ASCII values characters
decimal hexadecimal octal 0–8 \x0–\x8\0–\10control codes (NUL, etc.) ≠0000000000009 \x9\11tab (\t) ≠00≠0≠00000000010–13 \xA–\xD\12–\15whitespaces (\n, \v, \f, \r) ≠00≠000000000014–31 \xE–\x1F\16–\37control codes ≠00000000000032 \x20\40space 0≠0≠0≠00000000033–47 \x21–\x2F\41–\57!"#$%&'()*+,-./0≠000≠0≠000000048–57 \x30–\x39\60–\7101234567890≠000≠00≠0000≠0≠058–64 \x3A–\x40\72–\100:;<=>?@0≠000≠0≠000000065–70 \x41–\x46\101–\106ABCDEF0≠000≠00≠0≠0≠000≠071–90 \x47–\x5A\107–\132GHIJKLMNOP
QRSTUVWXYZ0≠000≠00≠0≠0≠000091–96 \x5B–\x60\133–\140[\]^_`0≠000≠0≠000000097–102 \x61–\x66\141–\146abcdef0≠000≠00≠0≠00≠00≠0103–122 \x67–\x7A\147–\172ghijklmnop
qrstuvwxyz0≠000≠00≠0≠00≠000123–126 \x7B–\x7E\172–\176{|}~0≠000≠0≠0000000127 \x7F\177backspace character (DEL) ≠000000000000