mbrtoc16 - cppreference.com (original) (raw)

Converts a single code point from its narrow multibyte character representation to its variable-length 16-bit wide character representation (typically, UTF-16).

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, and taking into account the current multibyte conversion state *ps). If the function determines that the next multibyte character in s is complete and valid, converts it to the corresponding 16-bit wide 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 mbrtoc16(NULL, "", 1, ps).

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

If the macro __STDC_UTF_16__ is defined, the 16-bit encoding used by this function is UTF-16; otherwise, it is implementation-defined. The macro is always defined and the encoding is always UTF-16.(since C23) In any case, the multibyte character encoding used by this function is specified by the currently active C locale.

[edit] Parameters

[edit] 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.
• (size_t)-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.
• (size_t)-2 if the next n bytes constitute an incomplete, but so far valid, multibyte character. Nothing is written to *pc16.
• (size_t)-1 if encoding error occurs. Nothing is written to *pc16, the value EILSEQ is stored in errno and the value of *ps is unspecified.

[edit] Example

On MSVC you may need the /utf-8 compiler flag for UTF_8 to work properly.

#include <locale.h> #include <stdio.h> #include <uchar.h>   int main(void) { setlocale(LC_ALL, "en_US.utf8"); const char in[] = u8"zß水🍌"; // or "z\u00df\u6c34\U0001F34C" enum { in_sz = sizeof in / sizeof in };   printf("Processing %d UTF-8 code units: [", in_sz); for (int n = 0; n < in_sz; ++n) printf("%s%02X", n ? " " : "", (unsigned char)in[n]); puts("]");   char16_t out[in_sz]; const char p_in = in; const char* end = in + in_sz; char16_t* p_out = out; mbstate_t state = {0};   for (size_t rc; (rc = mbrtoc16(p_out, p_in, end - p_in, &state));) { if (rc == (size_t)-1) // invalid input break; else if(rc == (size_t)-2) // truncated input break; else if(rc == (size_t)-3) // UTF-16 high surrogate p_out += 1; else { p_in += rc; p_out += 1; }; }   const size_t out_sz = p_out - out + 1; printf("into %zu UTF-16 code units: [", out_sz); for (size_t x = 0; x < out_sz; ++x) printf("%s%04X", x ? " " : "", out[x]); puts("]"); }

Output:

Processing 11 UTF-8 code units: [7A C3 9F E6 B0 B4 F0 9F 8D 8C 00] into 6 UTF-16 code units: [007A 00DF 6C34 D83C DF4C 0000]

[edit] References

• C23 standard (ISO/IEC 9899:2024):

• 7.30.1.3 The mbrtoc16 function (p: 408-409)

• C11 standard (ISO/IEC 9899:2011):

• 7.28.1.1 The mbrtoc16 function (p: 398-399)

[edit] See also