std::mbsinit

#include <clocale>
#include <cwchar>
#include <iostream>
#include <string>

int main()
{
    //  mbrlen()     UTF-8
    std::setlocale(LC_ALL, "en_US.utf8");
    //    UTF-8
    std::string str = ""; //  u8"\u6c34"  "\xe6\xb0\xb4"
    std::mbstate_t mb = std::mbstate_t();
    (void)std::mbrlen(&str[0], 1, &mb);
    if (!std::mbsinit(&mb))
        std::cout << "    " << str
                  << "     \n";

    (void)std::mbrlen(&str[1], str.size() - 1, &mb);
    if (std::mbsinit(&mb))
        std::cout << "   2  " << str
                  << ",    \n"
                  << " \n";
}