#include <stdbool.h>

#include <stdlib.h>

#include <string.h>

#include <wchar.h>

/* Do not include the above headers in the example.

*/

wchar_t *

mbstouwcs (const char *s)

{

  /* Include the null terminator in the conversion.  */

  size_t len = strlen (s) + 1;

  wchar_t *result = reallocarray (NULL, len, sizeof (wchar_t));

  if (result == NULL)

    return NULL;

  wchar_t *wcp = result;

  mbstate_t state;

  memset (&state, '\0', sizeof (state));

  while (true)

    {

      wchar_t wc;

      size_t nbytes = mbrtowc (&wc, s, len, &state);

      if (nbytes == 0)

        {

          /* Terminate the result string.  */

          *wcp = L'\0';

          break;

        }

      else if (nbytes == (size_t) -2)

        {

          /* Truncated input string.  */

          errno = EILSEQ;

          free (result);

          return NULL;

        }

      else if (nbytes == (size_t) -1)

        {

          /* Some other error (including EILSEQ).  */

          free (result);

          return NULL;

        }

      else

        {

          /* A character was converted.  */

          *wcp++ = towupper (wc);

          len -= nbytes;

          s += nbytes;

        }

    }

  return result;

}