Difference between revisions of "cpp/string/multibyte/mbstowcs"

Revision as of 02:30, 28 September 2017

Converts a multibyte character string from the array whose first element is pointed to by src to its wide character representation. Converted characters are stored in the successive elements of the array pointed to by dst. No more than len wide characters are written to the destination array.

Each character is converted as if by a call to std::mbtowc, except that the mbtowc conversion state is unaffected. The conversion stops if:

• The multibyte null character was converted and stored.
• An invalid (in the current C locale) multibyte character was encountered.
• The next wide character to be stored would exceed len.

Notes

In most implementations, this function updates a global static object of type std::mbstate_t as it processes through the string, and cannot be called simultaneously by two threads, std::mbsrtowcs should be used in such cases.

POSIX specifies a common extension: if dst is a null pointer, this function returns the number of wide characters that would be written to dst, if converted. Similar behavior is standard for std::mbsrtowcs.

Parameters

Return value

On success, returns the number of wide characters, excluding the terminating L'\0', written to the destination array.

On conversion error (if invalid multibyte character was encountered), returns static_cast<std::size_t> (-1).

Example

#include <iostream>
#include <clocale>
#include <cstdlib>
int main()
{
    std::setlocale(LC_ALL, "en_US.utf8");
    std::wcout.imbue(std::locale("en_US.utf8"));
    const char* mbstr = u8"z\u00df\u6c34\U0001f34c"; // or u8"zß水🍌"
                        // or "\x7a\xc3\x9f\xe6\xb0\xb4\xf0\x9f\x8d\x8c";
    wchar_t wstr[5];
    std::mbstowcs(wstr, mbstr, 5);
    std::wcout << "wide string: " << wstr << '\n';
}

wide string: zß水🍌

See also