std::islower(3) C++ Standard Libary std::islower(3) 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 ac- cording 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 un- signed 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 argu- ment 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 <cctype> #include <clocale> #include <iostream> int main() { unsigned char c = '\xe5'; // letter AY 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'; } Possible output: islower('\xe5', default C locale) returned false islower('\xe5', ISO-8859-1 locale) returned true See also islower(std::locale) checks if a character is classified as lowercase by a locale (function template) iswlower checks if a wide character is lowercase (function) C documentation for islower 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 0a8 \x0a\x8 \0a\10 control codes a 0 0 0 0 0 0 0 0 0 0 0 0 (NUL, etc.) 9 \x9 \11 tab (\t) a 0 0 a 0 a 0 0 0 0 0 0 0 0 0 whitespaces 10a13 \xAa\xD \12a\15 (\n, \v, \f, a 0 0 a 0 0 0 0 0 0 0 0 0 0 \r) 14a31 \xEa\x1F \16a\37 control codes a 0 0 0 0 0 0 0 0 0 0 0 0 32 \x20 \40 space 0 a 0 a 0 a 0 0 0 0 0 0 0 0 0 33a47 \x21a\x2F \41a\57 !"#$%&'()*+,-./ 0 a 0 0 0 a 0 a 0 0 0 0 0 0 0 48a57 \x30a\x39 \60a\71 0123456789 0 a 0 0 0 a 0 0 a 0 0 0 0 a 0 a 0 58a64 \x3Aa\x40 \72a\100 :;<=>?@ 0 a 0 0 0 a 0 a 0 0 0 0 0 0 0 65a70 \x41a\x46 \101a\106 ABCDEF 0 a 0 0 0 a 0 0 a 0 a 0 a 0 0 0 a 0 71a90 \x47a\x5A \107a\132 GHIJKLMNOP 0 a 0 0 0 a 0 0 a 0 a 0 a 0 0 0 0 QRSTUVWXYZ 91a96 \x5Ba\x60 \133a\140 [\]^_` 0 a 0 0 0 a 0 a 0 0 0 0 0 0 0 97a102 \x61a\x66 \141a\146 abcdef 0 a 0 0 0 a 0 0 a 0 a 0 0 a 0 0 a 0 103a122 \x67a\x7A \147a\172 ghijklmnop 0 a 0 0 0 a 0 0 a 0 a 0 0 a 0 0 0 qrstuvwxyz 123a126 \x7Ba\x7E \172a\176 {|}~ 0 a 0 0 0 a 0 a 0 0 0 0 0 0 0 127 \x7F \177 backspace a 0 0 0 0 0 0 0 0 0 0 0 0 character (DEL) http://cppreference.com 2024.06.10 std::islower(3)
NAME | Synopsis | Parameters | Return value | Notes | Example | Possible output: | See also
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