std:: tolower

Converts the given character to lowercase according to the character conversion rules defined by the currently installed C locale.

In the default "C" locale, the following uppercase letters ABCDEFGHIJKLMNOPQRSTUVWXYZ are replaced with respective lowercase letters abcdefghijklmnopqrstuvwxyz .

Parameters

Return value

Lowercase version of ch or unmodified ch if no lowercase version is listed in the current C locale.

Notes

Like all other functions from <cctype> , the behavior of std::tolower is undefined if the argument's value is neither representable as unsigned char nor equal to EOF . To use these functions safely with plain char s (or signed char s), the argument should first be converted to unsigned char :

char my_tolower(char ch)
{
    return static_cast<char>(std::tolower(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:

std::string str_tolower(std::string s)
{
    std::transform(s.begin(), s.end(), s.begin(),
                // static_cast<int(*)(int)>(std::tolower)         // wrong
                // [](int c){ return std::tolower(c); }           // wrong
                // [](char c){ return std::tolower(c); }          // wrong
                   [](unsigned char c){ return std::tolower(c); } // correct
                  );
    return s;
}

Example

#include <cctype>
#include <clocale>
#include <iostream>
 
int main()
{
    unsigned char c = '\xb4'; // the character Ž in ISO-8859-15
                              // but ´ (acute accent) in ISO-8859-1
 
    std::setlocale(LC_ALL, "en_US.iso88591");
    std::cout << std::hex << std::showbase;
    std::cout << "in iso8859-1, tolower('0xb4') gives " << std::tolower(c) << '\n';
    std::setlocale(LC_ALL, "en_US.iso885915");
    std::cout << "in iso8859-15, tolower('0xb4') gives " << std::tolower(c) << '\n';
}

in iso8859-1, tolower('0xb4') gives 0xb4
in iso8859-15, tolower('0xb4') gives 0xb8

See also

External links