std::basic_filebuf::seekoff

#include <iostream>
#include <fstream>
#include <locale>
int main()
{
    // prepare a 10-byte file holding 4 characters in UTF8
    std::ofstream("text.txt") << u8"z\u00df\u6c34\U0001d10b"; // or u8"zß水𝄋"
                                           // or "\x7a\xc3\x9f\xe6\xb0\xb4\xf0\x9d\x84\x8b";
 
    // open using a non-converting encoding
    std::ifstream f1("text.txt");
    std::cout << "f1's locale's encoding() returns "
              << std::use_facet<std::codecvt<char, char, std::mbstate_t>>(f1.getloc()).encoding() << '\n'
              << "pubseekoff(3, beg) returns " << f1.rdbuf()->pubseekoff(3, std::ios_base::beg) << '\n'
              << "pubseekoff(0, end) returns " << f1.rdbuf()->pubseekoff(0, std::ios_base::end) << '\n';;
 
    // open using UTF-8
    std::wifstream f2("text.txt");
    f2.imbue(std::locale("en_US.UTF-8"));
    std::cout << "f2's locale's encoding() returns "
              << std::use_facet<std::codecvt<wchar_t, char, std::mbstate_t>>(f2.getloc()).encoding() << '\n'
              << "pubseekoff(3, beg) returns " << f2.rdbuf()->pubseekoff(3, std::ios_base::beg) << '\n'
              << "pubseekoff(0, end) returns " << f2.rdbuf()->pubseekoff(0, std::ios_base::end) << '\n';
 
}