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 ofch is not representable asunsignedchar and is not equal toEOF.

[edit]Parameters

[edit]Return value

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

[edit]Notes

Like all other functions from<cctype>, the behavior ofstd::isalnum is undefined if the argument's value is neither representable asunsignedchar nor equal toEOF. To use these functions safely with plainchars (orsignedchars), the argument should first be converted tounsignedchar:

bool my_isalnum(char ch){return std::isalnum(static_cast<unsignedchar>(ch));}

Similarly, they should not be directly used with standard algorithms when the iterator's value type ischar orsignedchar. Instead, convert the value tounsignedchar first:

int count_alnums(conststd::string& s){returnstd::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[](unsignedchar c){return std::isalnum(c);}// correct);}

[edit]Example

#include <cctype>#include <clocale>#include <iostream> int main(){unsignedchar 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'; }

isalnum('\xdf', default C locale) returned falseisalnum('\xdf', ISO-8859-1 locale) returned true

[edit]See also

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