std::mbstowcs(3)

NAME
std::mbstowcs - std::mbstowcs

Synopsis
   Defined in header <cstdlib>
   std::size_t mbstowcs( wchar_t* dst, const char* src, std::size_t len );
   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
   dst - pointer to wide character array where the wide string will be stored
   src - pointer to the first element of a null-terminated multibyte string to convert
   len - number of wide characters available in the array pointed to by dst

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
// Run this code
 #include <clocale>
 #include <cstdlib>
 #include <iostream>
 int main()
 {
     std::setlocale(LC_ALL, "en_US.utf8");
     std::wcout.imbue(std::locale("en_US.utf8"));
     const char* mbstr = "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';
 }

Output:
 wide string: zß水🍌

See also
   mbsrtowcs converts a narrow multibyte character string to wide string, given state
             (function)
   wcstombs converts a wide string to narrow multibyte character string
             (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
   mbstowcs