NAME¶

std::mbrtoc16 - std::mbrtoc16

Synopsis¶

Defined in header <cuchar>
std::size_t mbrtoc16( char16_t* pc16,

const char* s, (since C++11)
std::size_t n,

std::mbstate_t* ps );

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::showbase;
for (unsigned char c: str)
std::cout << std::hex << +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::hex
<< static_cast<int>(c16) << " obtained from ";
if (rc == (std::size_t)-3)
std::cout << "earlier surrogate pair\n";
else if (rc == (std::size_t) - 2)
break;
else if (rc == (std::size_t) - 1)
break;
else
{
std::cout << std::dec << rc << " bytes [ ";
for (std::size_t n = 0; n < rc; ++n)
std::cout << std::hex << +static_cast<unsigned char>(ptr[n]) << ' ';
std::cout << "]\n";
ptr += rc;
}
}
}

Output:¶

Processing 10 bytes: [ 0x7a 0xc3 0x9f 0xe6 0xb0 0xb4 0xf0 0x9f 0x8d 0x8c ]
Next UTF-16 char: 0x7a obtained from 1 bytes [ 0x7a ]
Next UTF-16 char: 0xdf obtained from 2 bytes [ 0xc3 0x9f ]
Next UTF-16 char: 0x6c34 obtained from 3 bytes [ 0xe6 0xb0 0xb4 ]
Next UTF-16 char: 0xd83c obtained from 4 bytes [ 0xf0 0x9f 0x8d 0x8c ]
Next UTF-16 char: 0xdf4c obtained from earlier surrogate pair

See also¶

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