std::isalnum(3)

NAME
std::isalnum - std::isalnum

Synopsis
   Defined in header <cctype>
   int isalnum( int ch );
   Checks if the given character is an alphanumeric character as classified by the
   current C locale. In the default locale, the following characters are alphanumeric:
     * digits (0123456789)
     * uppercase letters (ABCDEFGHIJKLMNOPQRSTUVWXYZ)
     * lowercase letters (abcdefghijklmnopqrstuvwxyz)
   The behavior is undefined if the value of ch is not representable as unsigned char
   and is not equal to EOF.

Parameters
   ch - character to classify

Return value
   Non-zero value if the character is an alphanumeric character, 0 otherwise.

Notes
   Like all other functions from <cctype>, the behavior of std::isalnum is undefined if
   the argument's value is neither representable as unsigned char nor equal to EOF. To
   use these functions safely with plain chars (or signed chars), the argument should
   first be converted to unsigned char:
 bool my_isalnum(char ch)
 {
     return std::isalnum(static_cast<unsigned char>(ch));
 }
   Similarly, they should not be directly used with standard algorithms when the
   iterator's value type is char or signed char. Instead, convert the value to unsigned
   char first:
 int count_alnums(const std::string& s)
 {
     return std::count_if(s.begin(), s.end(),
                       // static_cast<int(*)(int)>(std::isalnum) // wrong
                       // [](int c){ return std::isalnum(c); } // wrong
                       // [](char c){ return std::isalnum(c); } // wrong
                        [](unsigned char c){ return std::isalnum(c); } // correct
                        );
 }

Example
   Demonstrates the use of std::isalnum with different locales (OS-specific). // Run this code
 #include <cctype>
 #include <clocale>
 #include <iostream>
 int main()
 {
     unsigned char c = '\xdf'; // German letter ß in ISO-8859-1
     std::cout << "isalnum(\'\\xdf\', default C locale) returned "
               << std::boolalpha << static_cast<bool>(std::isalnum(c)) << '\n';
     if (std::setlocale(LC_ALL, "de_DE.iso88591"))
         std::cout << "isalnum(\'\\xdf\', ISO-8859-1 locale) returned "
                   << static_cast<bool>(std::isalnum(c)) << '\n';
 }

Possible output:
 isalnum('\xdf', default C locale) returned false
 isalnum('\xdf', ISO-8859-1 locale) returned true

See also
   isalnum(std::locale) checks if a character is classified as alphanumeric by a locale
                        (function template)
   iswalnum checks if a wide character is alphanumeric
                        (function)
   C documentation for
   isalnum
        ASCII values characters iscntrl isprint isspace isblank isgraph ispunct isalnum isalpha isupper islower isdigit isxdigit decimal hexadecimal octal iswcntrl iswprint iswspace iswblank iswgraph iswpunct iswalnum iswalpha iswupper iswlower iswdigit iswxdigit 0–8 \x0–\x8 \0–\10 control codes ≠0 0 0 0 0 0 0 0 0 0 0 0
                        (NUL, etc.) 9 \x9 \11 tab (\t) ≠0 0 ≠0 ≠0 0 0 0 0 0 0 0 0
                        whitespaces 10–13 \xA–\xD \12–\15 (\n, \v, \f, ≠0 0 ≠0 0 0 0 0 0 0 0 0 0
                        \r) 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
                        QRSTUVWXYZ 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
                        qrstuvwxyz 123–126 \x7B–\x7E \172–\176 {|}~ 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0 127 \x7F \177 backspace ≠0 0 0 0 0 0 0 0 0 0 0 0
                        character (DEL)