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std::isalnum(3) C++ Standard Libary 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 clas- sified 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 oth- erwise. 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-spe- cific). // Run this code #include <cctype> #include <clocale> #include <iostream> int main() { unsigned char c = '\xdf'; // German letter 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 alphanu- meric 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 isw- print iswspace iswblank iswgraph iswpunct iswalnum iswalpha iswupper iswlower iswdigit iswxdigit 08 \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 1013 \xA\xD \12\15 (\n, \v, \f, 0 0 0 0 0 0 0 0 0 0 0 0 \r) 1431 \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 3347 \x21\x2F \41\57 !"#$%&'()*+,-./ 0 0 0 0 0 0 0 0 0 0 0 0 4857 \x30\x39 \60\71 0123456789 0 0 0 0 0 0 0 0 0 0 0 0 5864 \x3A\x40 \72\100 :;<=>?@ 0 0 0 0 0 0 0 0 0 0 0 0 6570 \x41\x46 \101\106 ABCDEF 0 0 0 0 0 0 0 0 0 0 0 0 7190 \x47\x5A \107\132 GHIJKLMNOP 0 0 0 0 0 0 0 0 0 0 0 0 QRSTUVWXYZ 9196 \x5B\x60 \133\140 [\]^_` 0 0 0 0 0 0 0 0 0 0 0 0 97102 \x61\x66 \141\146 abcdef 0 0 0 0 0 0 0 0 0 0 0 0 103122 \x67\x7A \147\172 ghijklmnop 0 0 0 0 0 0 0 0 0 0 0 0 qrstuvwxyz 123126 \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) http://cppreference.com 2024.06.10 std::isalnum(3)
NAME | Synopsis | Parameters | Return value | Notes | Example | Possible output: | See also
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