std::c16rtomb

std::size_t c16rtomb( char* s, char16_t c16, std::mbstate_t* ps );

Converts a UCS-2 code point to narrow multibyte character.

If s is not a null pointer, the function determines the number of bytes necessary to store the multibyte character representation of c16 (including any shift sequences), and stores the multibyte character representation in the character array whose first element is pointed to by s. At most MB_CUR_MAX bytes can be written by this function.

If s is a null pointer, the call is equivalent to std::c16rtomb(buf, u'\0', ps) for some internal buffer buf.

If c16 is the null wide character u'\0', a null byte is stored, preceded by any shift sequence necessary to restore the initial shift state and the conversion state parameter *ps is updated to represent the initial shift state.

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

Parameters

Return value

On success, returns the number of bytes (including any shift sequences) written to the character array whose first element is pointed to by s. This value may be ​0​, e.g. when processing the first char16_t in a surrogate pair.

On failure (if c16 is not a valid 16-bit character), returns -1, stores EILSEQ in errno, and leaves *ps in unspecified state.

Notes

Unlike std::mbrtoc16, which converts variable-width multibyte (such as UTF-8) to variable-width 16-bit (such as UTF-16) encoding, this function can only convert single-unit 16-bit encoding, meaning it cannot convert UTF-16 to UTF-8.

Example

#include <iostream>
#include <iomanip>
#include <clocale>
#include <cuchar>
#include <cstdlib>
 
int main()
{
    std::setlocale(LC_ALL, "en_US.utf8");
    std::u16string str = u"zß水";
    std::cout << "Processing " << str.size() << " UTF-16 code units: [ ";
    for(char16_t c : str) std::cout << std::showbase << std::hex << c << ' ';
    std::cout << "]\n";
 
    std::mbstate_t state{};
    std::string out(MB_CUR_MAX, '\0');
    for(size_t n = 0; n < str.size(); ++n)
    {   
        int rc = std::c16rtomb(&out[0], str[n], &state);
        std::cout << str[n] << " converted to [ ";
        for(int x = 0; x < rc; ++x) std::cout << +(unsigned char)out[x] << ' ';
        std::cout << "]\n";
    }
}

Processing 3 UTF-16 code units: [ 0x7a 0xdf 0x6c34 ]
0x7a converted to [ 0x7a ]
0xdf converted to [ 0xc3 0x9f ]
0x6c34 converted to [ 0xe6 0xb0 0xb4 ]

See also