std::mbrtoc16

 

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Null-terminated multibyte strings

Functions Wide/multibyte examination mblen mbrlen mbsinit Multibyte/wide conversions mbtowc mbstowcs btowc mbrtowc mbsrtowcs    wctomb wcstombs wctob wcrtomb wcsrtombs mbrtoc8 (C++20) mbrtoc16 (C++11) mbrtoc32 (C++11) c8rtomb (C++20) c16rtomb (C++11) c32rtomb (C++11)

Types

mbstate_t

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MB_LEN_MAX MB_CUR_MAX __STDC_UTF_16__ __STDC_UTF_32__ (C++11)(C++11)

 

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)

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

c16rtomb (C++11)	converts a UTF-16 character to narrow multibyte encoding (function)
mbrtoc8 (C++20)	converts a narrow multibyte character to UTF-8 encoding (function)
do_in [virtual]	converts a string from ExternT to InternT, such as when reading from file (virtual protected member function of std::codecvt<InternT,ExternT,StateT>)
C documentation for mbrtoc16