< cpp‎ | locale
Defined in header <locale>
template< class charT >
bool isalnum( charT ch, const locale& loc );

Checks if the given character classified as an alphanumeric character by the given locale's std::ctype facet.


ch - character
loc - locale

Return value

Returns true if the character is classified as alphanumeric, false otherwise.

Possible implementation

template< class charT >
bool isalnum( charT ch, const std::locale& loc ) {
    return std::use_facet<std::ctype<charT>>(loc).is(std::ctype_base::alnum, ch);


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

#include <iostream>
#include <locale>
int main()
    const wchar_t c = L'\u2135'; // mathematical symbol aleph
    std::locale loc1("C");
    std::cout << "isalnum('ℵ', C locale) returned "
               << std::boolalpha << std::isalnum(c, loc1) << '\n';
    std::locale loc2("en_US.UTF-8");
    std::cout << "isalnum('ℵ', Unicode locale) returned "
              << std::boolalpha << std::isalnum(c, loc2) << '\n';


isalnum('ℵ​', C locale) returned false
isalnum('ℵ', Unicode locale) returned true

See also

checks if a character is alphanumeric
checks if a wide character is alphanumeric