How to make string16 from INT in C++?

Question

C++ / C#

I have an int variable that contains a number equal to the utf8 character code (for m it will be 1084). Here's how I can make it so that the character that means this number is written to the string16 variable?

Answer 1

From documentation:

String class for 16-bit characters.
This is an instantiation of the basic_string class template that uses char16_t as the character type

Then something like this

int code = ...;
std::u16string str("");

str += (char16_t)code;

Answer 2

UTF-8 is a multibyte character set and has no codes. So we consider that we are dealing with Unicode codes.
This is just a piece of my mini-library, so...
The template was used to automatically specialize wchar_t to the correct length, there are actually versions for 1 and 2.

namespace str{

enum {
    SURROGATE_MIN = 0xD800,
    SURROGATE_MAX = 0xDFFF,
    SURROGATE_LO_MIN = SURROGATE_MIN,
    SURROGATE_HI_MIN = 0xDC00,
    SURROGATE_LO_MAX = SURROGATE_HI_MIN - 1,
    SURROGATE_HI_MAX = SURROGATE_MAX,
    UNICODE_MAX = 0x10FFFF,
    U8_1BYTE_MAX = 0x7F,
    U8_2BYTE_MIN = 0x80,
    U8_2BYTE_MAX = 0x7FF,
    U8_3BYTE_MIN = 0x800,
    U8_3BYTE_MAX = 0xFFFF,
    U8_4BYTE_MIN = 0x10000,
    U8_4BYTE_MAX = UNICODE_MAX,
    U16_1WORD_MAX = 0xFFFF,
    U16_2WORD_MIN = 0x10000,
    U16_2WORD_MAX = UNICODE_MAX,
};

template <int Len>
void putCpNeT (wchar_t*& p, unsigned long aCp);

///  Puts a code-point in wchar_t encoding, w/o error-checking
///  @param [in,out]  p     position to put to
///  @param [in]      aCp   code-point, surely valid
inline void putCpNe (wchar_t*& p, unsigned long aCp)
    { putCpNeT<sizeof(wchar_t)>(p, aCp); }

} // namespace str

template <>
void str::putCpNeT<2> (wchar_t*& p, unsigned long aCp)
{
    if (aCp < U16_2WORD_MIN) {  // 1 word
        *(p++) = static_cast<wchar_t>(aCp);
    } else if (aCp <= U16_2WORD_MAX) {    // 2 words
        aCp -= U16_2WORD_MIN;
        // Hi word
        const wchar_t lo10 = aCp & 0x3FF;
        const wchar_t hi10 = aCp >> 10;
        *(p++) = static_cast<wchar_t>(0xD800 | hi10);
        *(p++) = static_cast<wchar_t>(0xDC00 | lo10);
    }
}

void str::appendCp(std::wstring& s, unsigned long aCp)
{
    wchar_t c[5];
    wchar_t* end = c;
    putCpNe(end, aCp);
    s.append(c, end);
}