1  #include <stdbool.h>
       2  #include <stdlib.h>
       3  #include <string.h>
       4  #include <wchar.h>
       5  
       6  /* Do not include the above headers in the example.
       7  */
       8  wchar_t *
       9  mbstouwcs (const char *s)
      10  {
      11    /* Include the null terminator in the conversion.  */
      12    size_t len = strlen (s) + 1;
      13    wchar_t *result = reallocarray (NULL, len, sizeof (wchar_t));
      14    if (result == NULL)
      15      return NULL;
      16  
      17    wchar_t *wcp = result;
      18    mbstate_t state;
      19    memset (&state, '\0', sizeof (state));
      20  
      21    while (true)
      22      {
      23        wchar_t wc;
      24        size_t nbytes = mbrtowc (&wc, s, len, &state);
      25        if (nbytes == 0)
      26          {
      27            /* Terminate the result string.  */
      28            *wcp = L'\0';
      29            break;
      30          }
      31        else if (nbytes == (size_t) -2)
      32          {
      33            /* Truncated input string.  */
      34            errno = EILSEQ;
      35            free (result);
      36            return NULL;
      37          }
      38        else if (nbytes == (size_t) -1)
      39          {
      40            /* Some other error (including EILSEQ).  */
      41            free (result);
      42            return NULL;
      43          }
      44        else
      45          {
      46            /* A character was converted.  */
      47            *wcp++ = towupper (wc);
      48            len -= nbytes;
      49            s += nbytes;
      50          }
      51      }
      52    return result;
      53  }