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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 unsigned char and is not equal to EOF .

[edit] Parameters

[edit] Return value

Non-zero value if the character is a lowercase letter, zero otherwise.

[edit] 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
 );
}

[edit] Example

#include <cctype>
#include <clocale>
#include <iostream>
 
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';
 
}

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

[edit] See also

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