std::cout.imbue() 多次调用

Question

Compiler : Visual Studio 2019(C++20, latest)
I have a question about std::locale
Is it impossible to call std::cout.imbue multiple?
Why is it impossible?

When I ran below code.. I can see two of question mark(??) after second imbue function call..

#include <iomanip>
#include <iostream>
#include <locale>

int main()
{
    auto loc = std::locale("de_DE.utf8");
    std::cout.imbue(loc);
    std::cout << "locale_name = " << std::cout.getloc().name() << std::endl;
    std::cout << 100.50 << std::endl;
    std::cout << std::showbase << std::put_money(1050) << std::endl;

    std::cout.imbue(loc);   // no output below
    std::cout << "locale_name = " << std::cout.getloc().name() << std::endl;
    std::cout << 100.50 << std::endl;
    std::cout << std::showbase << std::put_money(1050) << std::endl;
}

Here is output
locale_name = de_DE.utf8
100,5
10,50 ??

Answer 1

There is no such restriction, and the output for me is:

locale_name = de_DE.utf8
100,5
10,50 €
locale_name = de_DE.utf8
100,5
10,50 €

Note that the Euro symbol may be replaced by weird stuff like ?? if your output terminal is not properly configured to show UTF-8 characters, or if that glyph is missing in your terminal's font.

For example, from memory, Visual Studio's output console either does not support Unicode or always decodes as UTF-16. One of the two. Probably the latter.

Besides that, if you get output different from the above, that would be an interesting standard library bug in your implementation.