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    std::mbrtoc16

    From cppreference.com
     
    C++
     
    Text processing library
     
    Null-terminated multibyte strings
     
    Defined in header <cuchar>
    std::size_t mbrtoc16( char16_t* pc16, const char* s, std::size_t n, std::mbstate_t* ps );
    		 (since C++11)
    See More

    Converts a narrow multibyte character to UTF-16 character representation.

    If s is not a null pointer, inspects at most n bytes of the multibyte character string, beginning with the byte pointed to by s to determine the number of bytes necessary to complete the next multibyte character (including any shift sequences). If the function determines that the next multibyte character in s is complete and valid, converts it to the corresponding 16-bit character and stores it in *pc16 (if pc16 is not null).

    If the multibyte character in *s corresponds to a multi-char16_t sequence (e.g., a surrogate pair in UTF-16), then after the first call to this function, *ps is updated in such a way that the next call to mbrtoc16 will write out the additional char16_t, without considering *s.

    If s is a null pointer, the values of n and pc16 are ignored and the call is equivalent to std::mbrtoc16(nullptr, "", 1, ps).

    If the wide character produced is the null character, the conversion state *ps represents the initial shift state.

    The multibyte encoding used by this function is specified by the currently active C locale.

    Parameters

    pc16 - pointer to the location where the resulting 16-bit character will be written
    s - pointer to the multibyte character string used as input
    n - limit on the number of bytes in s that can be examined
    ps - pointer to the conversion state object used when interpreting the multibyte string

    Return value

    The first of the following that applies:

    • 0 if the character converted from s (and stored in *pc16 if non-null) was the null character.
    • the number of bytes [1, n] of the multibyte character successfully converted from s.
    • -3 if the next char16_t from a multi-char16_t character (e.g., a surrogate pair) has now been written to *pc16. No bytes are processed from the input in this case.
    • -2 if the next n bytes constitute an incomplete, but so far valid, multibyte character. Nothing is written to *pc16.
    • -1 if encoding error occurs. Nothing is written to *pc16, the value EILSEQ is stored in errno and the value of *ps is unspecified.

    Example

    Run this code
    #include <clocale>
#include <cstring>
#include <cuchar>
#include <cwchar>
#include <iomanip>
#include <iostream>

int main()
{
    std::setlocale(LC_ALL, "en_US.utf8");

    std::string str{"z\u00df\u6c34\U0001F34C"}; // or u8"zß水🍌"

    std::cout << "Processing " << str.size() << " bytes: [" << std::uppercase
              << std::setfill('0') << std::hex;
    for (int n{}; unsigned char c : str)
        std::cout << (n++ ? " " : "") << +c;
    std::cout << "]\n";

    std::mbstate_t state{}; // zero-initialized to initial state
    char16_t c16{};
    const char* ptr{&str[0]}, *end{&str[0] + str.size()};

    while (std::size_t rc{std::mbrtoc16(&c16, ptr, end - ptr + 1, &state)})
    {
        std::cout << "Next UTF-16 char: " << std::setw(4)
                  << static_cast<unsigned short>(c16) << " obtained from ";
        if (rc == std::size_t(-3))
            std::cout << "earlier surrogate pair\n";
        else if (rc == std::size_t(-2))
            continue;
        else if (rc == std::size_t(-1))
            break;
        else
        {
            std::cout << std::dec << rc << " bytes [";
            for (std::size_t n{}; n != rc; ++n)
                std::cout << (n ? " " : "") << std::hex
                          << +static_cast<unsigned char>(ptr[n]);
            std::cout << "]\n";
            ptr += rc;
        }
    }
}

    Output: 

    Processing 10 bytes: [7A C3 9F E6 B0 B4 F0 9F 8D 8C]
Next UTF-16 char: 007A obtained from 1 bytes [7A]
Next UTF-16 char: 00DF obtained from 2 bytes [C3 9F]
Next UTF-16 char: 6C34 obtained from 3 bytes [E6 B0 B4]
Next UTF-16 char: D83C obtained from 4 bytes [F0 9F 8D 8C]
Next UTF-16 char: DF4C obtained from earlier surrogate pair

    See also

    (C++11)
    		 converts a UTF-16 character to narrow multibyte encoding
    (function) [edit]
    (C++20)
    		 converts a narrow multibyte character to UTF-8 encoding
    (function) [edit]
    [virtual]
    		 converts a string from ExternT to InternT, such as when reading from file
    (virtual protected member function of std::codecvt<InternT,ExternT,StateT>) [edit]
    C documentation for mbrtoc16