C String to lowercase with custom locale-CodePudding

I've been trying to call std::tolower() with a different locale but it seems that something is going wrong. My code is as follows:

int main() {
    std::locale::global(std::locale("es_ES.UTF-8"));
    std::thread(&function, this); // Repeated some times
    // wait for threads
}

void function() {
    std::string word = "HeÉllO";
    std::transform(word.begin(), word.end(), word.begin(), cToLower);
}

int cToLower(int c) {
    return std::tolower(c, std::locale());
}

So when I try to execute this program I get:

terminate called after throwing an instance of 'std::bad_cast'
terminate called recursively
  what():  std::bad_cast
Aborted (core dumped)

Although executing return std::tolower(c); works fine, but it just converts the 'standard' characters to lower, and not É.

I have some threads which are executing the same function simultaneously, using C 11 and compiling with g (in case it has something to do with it).

I was wondering if this is the correct way to implement what I want to do, or there's some other way of doing it.

Thanks!

CodePudding user response：

Unlike the version of tolower that came from C (which takes characters converted to unsigned char and then to int), the <locale> version of tolower is meant to be called with characters directly. It is defined to use the std::ctype<charT> facet of the locale, and the only two std::ctype specializations guaranteed to be available are std::ctype<char> and std::ctype<wchar_t>. Thus:

char cToLower(char c) {
    return std::tolower(c, std::locale());
}

Note that this is still a char-by-char transform; if the character occupies more than one byte, it is unlikely to handle it properly.

CodePudding user response：

Check if locale you are trying to use installed on your system. For example I have to install Spanish locale before code below stop crashing. Additionally you could work with wstring instead. Update: after some digging here is good explanation of using wstring - all cons and procs (cons mostly).

#include <thread>
#include <locale>
#include <algorithm> 
#include <iostream>

//forward declaration
void function();

int main() {
    std::locale::global(std::locale("es_ES.utf8"));
    std::thread test(&function);
    test.join();
}

wchar_t cToLower(wchar_t c) {        
    return std::tolower(c, std::locale());    
}

void function() {
    std::wstring word = L"HeÉllO";
    std::transform(word.begin(), word.end(), word.begin(), cToLower);
    std::wcout << word;
}

Output:

heéllo