Strange interaction between setlocale and mbstowcs

Question

I have a strange behaviour between setlocale and mbstowcs.

Here is a sample code :

#include <cstdlib>
#include <iostream>
#include <clocale>

int main()
{
    std::setlocale(LC_CTYPE, "");
    char * cur_ctype_locale = std::setlocale(LC_CTYPE, NULL); // line 1
    std::cout << cur_ctype_locale << std::endl; // line 2
    std::string src = "éèùç";
    size_t result_size = std::mbstowcs(NULL, &src[0], 0);
    if (result_size == (size_t)-1)
    {
        std::cout << "failed" << std::endl;
        return 1;
    }
    std::wstring result;
    result.resize(result_size + 1);
    result_size = std::mbstowcs(&result[0], &src[0], result_size + 1);
    std::wcout << result << std::endl;
    return 0;
}

When executed (on linux), the output is garbage.

When I remove the lines commented as "line 1" and "line 2" the output is correct (I see the string as defined in the sources).

As far as I read on the documentation of setlocale:

If locale is NULL, the current locale is only queried, not modified.

The lines commented as "line 1" and "line 2" should only return the current locale for LC_CTYPE and not modify the locale.

Am I missing something here ?

Thank you for your attention.

Does https://stackoverflow.com/questions/8947949/mixing-cout-and-wcout-in-same-program answer your question? Practice making an [mcve] - you could notice, that if you comment only line 2, the output is correct. Your issue is unrelated to mbstowcs. — KamilCuk, Oct 31 '22 at 03:14

score 0 · Answer 1 · answered Oct 30 '22 at 23:58

I'm running Archlinux and my the output of my locale:

LANG=en_US.UTF-8
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_PAPER="en_US.UTF-8"
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT="en_US.UTF-8"
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=

And running this code:

#include <string.h>
#include <errno.h>
#include <cstdlib>
#include <iostream>
#include <clocale>

int main()
{
    std::setlocale(LC_CTYPE, "");
    char * cur_ctype_locale = std::setlocale(LC_CTYPE, NULL); // line 1
    std::cout << cur_ctype_locale << std::endl; // line 2
    std::string src = "éèùç";
    size_t result_size = std::mbstowcs(NULL, &src[0], 0);
    if (result_size == (size_t)-1)
    {
        std::cout << "failed" << std::endl;
        return 1;
    }
    std::wstring result;
    result.resize(result_size + 1);
    result_size = std::mbstowcs(&result[0], &src[0], result_size + 1);
    if (result_size < 0) {
        std::cout << strerror(errno) << std::endl;
        printf("You error'd\n");
    } else {
        printf("You were fine...\n");
    }

    std::wcout << result << std::endl;
    return 0;
}

And the output:

en_US.UTF-8
You were fine...

If you can provide some information say your output from running locale?

Other than that as you say by calling setlocale with NULL you're strictly querying at this point.

score 0 · Answer 2 · answered Oct 31 '22 at 03:12

0

std::cout <<
std::wcout <<

It's either one or the other, you can't use both.

answered Oct 31 '22 at 03:12

KamilCuk

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Strange interaction between setlocale and mbstowcs

2 Answers2