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

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)

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 0–8 \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 10–13 \xA–\xD \12–\15 (\n, \v, \f, ?? 0 0 ?? 0 0 0 0 0 0 0 0 0 0
\r) 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–\106 ABCDEF 0 ?? 0 0 0 ?? 0 0 ?? 0 ?? 0 ?? 0 0 0 ?? 0 71–90 \x47–\x5A \107–\132 GHIJKLMNOP 0 ?? 0 0 0 ?? 0 0 ?? 0 ?? 0 ?? 0 0 0 0
QRSTUVWXYZ 91–96 \x5B–\x60 \133–\140 [\]^_` 0 ?? 0 0 0 ?? 0 ?? 0 0 0 0 0 0 0 97–102 \x61–\x66 \141–\146 abcdef 0 ?? 0 0 0 ?? 0 0 ?? 0 ?? 0 0 ?? 0 0 ?? 0 103–122 \x67–\x7A \147–\172 ghijklmnop 0 ?? 0 0 0 ?? 0 0 ?? 0 ?? 0 0 ?? 0 0 0
qrstuvwxyz 123–126 \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)