std::tolower example from website not giving expected result

July 14, 2022

I found an example of std::tolower, here: https://en.cppreference.com/w/cpp/string/byte/islower

There’s an example which, according to the website, should return false and true for this bit of 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';
 
}

But copy-pasting this bit in my own IDE gives me false and false, and so does the run this code button on the website itself.

EDIT:
So the locale is not being set properly. Using windows 10 with latest Jetbrains Rider.

This works:

    assert(std::setlocale(LC_ALL, "en_US.UTF-8"));
    //assert(std::setlocale(LC_ALL, "en_GB.iso88591"));

    printf ("Locale is: %s\n", setlocale(LC_ALL,NULL) );

But uncommenting the other locale will throw error.

>Solution :

Ok so problem is that on Windows locale names are not same as on Linux.

On Windows iso88591 is represented by codepage 1252 so one of possible locale name is:.1252:

std::setlocale(LC_ALL, ".1252");

Not sure, but it is possible also .Windows-1252 will do the job too.

You can also try boost.locale to try unify locale names (so it could work same on all platforms). Since this is C++ you need to use std::tolower(std::locale).