From cppreference.com
intislower(intch);Checks if the given character is classified as a lowercase character according to the current C locale. In the default "C" locale, std::islower returns a nonzero value only for the lowercase letters (abcdefghijklmnopqrstuvwxyz).
If islower returns a nonzero value, it is guaranteed that std::iscntrl, std::isdigit, std::ispunct, and std::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 unsignedchar 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
, the behavior of std::islower is undefined if the argument's value is neither representable as unsignedchar nor equal to EOF. To use these functions safely with plain chars (or signedchars), the argument should first be converted to unsignedchar:
boolmy_islower(charch){returnstd::islower(static_cast<unsignedchar>(ch));}Similarly, they should not be directly used with standard algorithms when the iterator's value type is char or signedchar. Instead, convert the value to unsignedchar first:
intcount_lowers(conststd::string&s){returnstd::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[](unsignedcharc){returnstd::islower(c);}// correct);}Example
Run this code
#include<cctype>#include<clocale>#include<iostream>intmain(){unsignedcharc='\xe5';// letter å in ISO-8859-1std::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';}Possible output:
islower('\xe5', default C locale) returned false islower('\xe5', ISO-8859-1 locale) returned true See also
ASCII values characters
decimal hexadecimal octal 0–8 \x0–\x8\0–\10control codes (NUL, etc.) ≠0000000000009 \x9\11tab (\t) ≠00≠0≠00000000010–13 \xA–\xD\12–\15whitespaces (\n, \v, \f, \r) ≠00≠000000000014–31 \xE–\x1F\16–\37control codes ≠00000000000032 \x20\40space 0≠0≠0≠00000000033–47 \x21–\x2F\41–\57!"#$%&'()*+,-./0≠000≠0≠000000048–57 \x30–\x39\60–\7101234567890≠000≠00≠0000≠0≠058–64 \x3A–\x40\72–\100:;<=>?@0≠000≠0≠000000065–70 \x41–\x46\101–\106ABCDEF0≠000≠00≠0≠0≠000≠071–90 \x47–\x5A\107–\132GHIJKLMNOP
QRSTUVWXYZ0≠000≠00≠0≠0≠000091–96 \x5B–\x60\133–\140[\]^_`0≠000≠0≠000000097–102 \x61–\x66\141–\146abcdef0≠000≠00≠0≠00≠00≠0103–122 \x67–\x7A\147–\172ghijklmnop
qrstuvwxyz0≠000≠00≠0≠00≠000123–126 \x7B–\x7E\172–\176{|}~0≠000≠0≠0000000127 \x7F\177backspace character (DEL) ≠000000000000