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In the standard document of N4606 ISO/IEC JTC1 SC22 WG21, http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf p.34 there is an example.

long double operator "" _w(long double);
std::string operator "" _w(const char16_t*, std::size_t);
unsigned operator "" _w(const char*);
int main() {
  1.2_w; // calls operator "" _w(1.2L)
  u"one"_w; // calls operator "" _w(u"one", 3) 
  12_w; // calls operator "" _w("12")
  "two"_w; // error: no applicable literal operator
}

How can I make an example of std::string operator "" _w(const char16_t*, std::size_t);

How can I convert from const char16_t * to std::string.

Other 2 functions are like this.

long double operator "" _w(long double ld){return ld;}
unsigned operator "" _w(const char*cc){return (unsigned)*cc};
Bo Persson
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Kiyoshi Ogawa
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  • Take a look at: https://stackoverflow.com/questions/402283/stdwstring-vs-stdstring, particularly [this answer](https://stackoverflow.com/questions/402283/stdwstring-vs-stdstring#402918). – Jens Apr 14 '18 at 10:42
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    That's just an example of overload resolution, not intended to do anything practical. – Bo Persson Apr 14 '18 at 10:45
  • well it really depends on the encoded data you wanna support. utf16 -> utf8 conversion? – Thomas Apr 14 '18 at 13:49

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