std::wctomb (3) - Linux Manuals

std::wctomb: std::wctomb


std::wctomb - std::wctomb


Defined in header <cstdlib>
int wctomb( char *s, wchar_t wc );

Converts a wide character wc to multibyte encoding and stores it (including any shift sequences) in the char array whose first element is pointed to by s. No more than MB_CUR_MAX characters are stored.
If wc is the null character, the null byte is written to s, preceded by any shift sequences necessary to restore the initial shift state.
If s is a null pointer, resets the global conversion state and determines whether shift sequences are used.


s - pointer to the character array for output
wc - wide character to convert

Return value

If s is not a null pointer, returns the number of bytes that are contained in the multibyte representation of wc or -1 if wc is not a valid character.
If s is a null pointer, resets its internal conversion state to represent the initial shift state and returns 0 if the current multibyte encoding is not state-dependent (does not use shift sequences) or a non-zero value if the current multibyte encoding is state-dependent (uses shift sequences).


Each call to wctomb updates the internal global conversion state (a static object of type std::mbstate_t, only known to this function). If the multibyte encoding uses shift states, this function is not reentrant. In any case, multiple threads should not call wctomb without synchronization: std::wcrtomb may be used instead.


// Run this code

  #include <iostream>
  #include <clocale>
  #include <string>
  #include <cstdlib>

  void print_wide(const std::wstring& wstr)
      bool shifts = std::wctomb(nullptr, 0); // reset the conversion state
      std::cout << "shift sequences " << (shifts ? "are" : "not" ) << " used\n";
      for (wchar_t wc : wstr) {
          std::string mb(MB_CUR_MAX, '\0');
          int ret = std::wctomb(&mb[0], wc);
          std::cout << "multibyte char " << mb << " is " << ret << " bytes\n";

  int main()
      std::setlocale(LC_ALL, "en_US.utf8");
      // UTF-8 narrow multibyte encoding
      std::wstring wstr = L"z\u00df\u6c34\U0001d10b"; // or L"zß水𝄋"


  shift sequences not used
  multibyte char z is 1 bytes
  multibyte char ß is 2 bytes
  multibyte char ć°´ is 3 bytes
  multibyte char 𝄋 is 4 bytes

See also

          converts the next multibyte character to wide character
mbtowc (function)
          converts a wide character to its multibyte representation, given state
wcrtomb (function)

do_out converts a string from internT to externT, such as when writing to file
          (virtual protected member function of std::codecvt<InternT,ExternT,State>)