std::islower (3) - Linux Man Pages

std::islower: std::islower

NAME

std::islower - std::islower

Synopsis


Defined in header <cctype>
int islower( int ch );


Checks if the given character is classified as a lowercase character according to the current C locale. In the default "C" locale, islower returns a nonzero value only for the lowercase letters (abcdefghijklmnopqrstuvwxyz).
If islower returns a nonzero value, it is guaranteed that iscntrl, isdigit, ispunct, and isspace return zero for the same character in the same C locale.
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 a lowercase letter, zero otherwise.

Notes


Like all other functions from <cctype>, the behavior of std::islower 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_islower(char ch)
  {
      return std::islower(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_lowers(const std::string& s)
  {
      return std::count_if(s.begin(), s.end(),
                        // static_cast<int(*)(int)>(std::islower) // wrong
                        // [](int c){ return std::islower(c); } // wrong
                        // [](char c){ return std::islower(c); } // wrong
                           [](unsigned char c){ return std::islower(c); } // correct
                          );
  }

Example


// Run this code


  #include <iostream>
  #include <cctype>
  #include <clocale>


  int main()
  {
      unsigned char c = '\xe5'; // letter å in ISO-8859-1


      std::cout << "islower(\'\\xe5\', default C locale) returned "
                 << std::boolalpha << (bool)std::islower(c) << '\n';


      std::setlocale(LC_ALL, "en_GB.iso88591");
      std::cout << "islower(\'\\xe5\', ISO-8859-1 locale) returned "
                << std::boolalpha << (bool)std::islower(c) << '\n';


  }

Output:


  islower('\xe5', default C locale) returned false
  islower('\xe5', ISO-8859-1 locale) returned true

See also


                     checks if a character is classified as lowercase by a locale
islower(std::locale) (function template)
                     checks if a wide character is lowercase
iswlower (function)


ASCII values iscntrl isprint isspace isblank isgraph ispunct isalnum isalpha isupper islower isdigit isxdigit
decimal hexadecimal octal characters iswcntrl iswprint iswspace iswblank iswgraph iswpunct iswalnum iswalpha iswupper iswlower iswdigit iswxdigit


0–8 \x0–\x8 \0–\10 control codes (NUL, etc.) ≠0 0 0 0 0 0 0 0 0 0 0 0
9 \x9 \11 tab (\t) ≠0 0 ≠0 ≠0 0 0 0 0 0 0 0 0
10–13 \xA–\xD \12–\15 whitespaces (\n, \v, \f, \r) ≠0 0 ≠0 0 0 0 0 0 0 0 0 0
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–\10ABCDEF 0 ≠0 0 0 ≠0 0 ≠0 ≠0 ≠0 0 0 ≠0
71–90 \x47–\x5A \107–\13GHIJKLMNOP 0 ≠0 0 0 ≠0 0 ≠0 ≠0 ≠0 0 0 0
                              QRSTUVWXYZ
91–96 \x5B–\x60 \133–\14[\]^_` 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
97–102\x61–\x66 \141–\14abcdef 0 ≠0 0 0 ≠0 0 ≠0 ≠0 0 ≠0 0 ≠0
103–12\x67–\x7A \147–\17ghijklmnop 0 ≠0 0 0 ≠0 0 ≠0 ≠0 0 ≠0 0 0
                              qrstuvwxyz
123–12\x7B–\x7E \172–\17{|}~ 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
127 \x7F \177 backspace character (DEL) ≠0 0 0 0 0 0 0 0 0 0 0 0