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<h4 class="subsection">6.3.5 A Complete Multibyte Conversion Example</h4>

<p>The example programs given in the last sections are only brief and do
not contain all the error checking, etc.  Presented here is a complete
and documented example.  It features the <code>mbrtowc</code> function but it
should be easy to derive versions using the other functions.

<pre class="smallexample">     int
     file_mbsrtowcs (int input, int output)
     {
       /* <span class="roman">Note the use of </span><code>MB_LEN_MAX</code><span class="roman">.</span>
          <code>MB_CUR_MAX</code><span class="roman"> cannot portably be used here.</span>  */
       char buffer[BUFSIZ + MB_LEN_MAX];
       mbstate_t state;
       int filled = 0;
       int eof = 0;
     
       /* <span class="roman">Initialize the state.</span>  */
       memset (&amp;state, '\0', sizeof (state));
     
       while (!eof)
         {
           ssize_t nread;
           ssize_t nwrite;
           char *inp = buffer;
           wchar_t outbuf[BUFSIZ];
           wchar_t *outp = outbuf;
     
           /* <span class="roman">Fill up the buffer from the input file.</span>  */
           nread = read (input, buffer + filled, BUFSIZ);
           if (nread &lt; 0)
             {
               perror ("read");
               return 0;
             }
           /* <span class="roman">If we reach end of file, make a note to read no more.</span> */
           if (nread == 0)
             eof = 1;
     
           /* <code>filled</code><span class="roman"> is now the number of bytes in </span><code>buffer</code><span class="roman">.</span> */
           filled += nread;
     
           /* <span class="roman">Convert those bytes to wide characters--as many as we can.</span> */
           while (1)
             {
               size_t thislen = mbrtowc (outp, inp, filled, &amp;state);
               /* <span class="roman">Stop converting at invalid character;</span>
                  <span class="roman">this can mean we have read just the first part</span>
                  <span class="roman">of a valid character.</span>  */
               if (thislen == (size_t) -1)
                 break;
               /* <span class="roman">We want to handle embedded NUL bytes</span>
                  <span class="roman">but the return value is 0.  Correct this.</span>  */
               if (thislen == 0)
                 thislen = 1;
               /* <span class="roman">Advance past this character.</span> */
               inp += thislen;
               filled -= thislen;
               ++outp;
             }
     
           /* <span class="roman">Write the wide characters we just made.</span>  */
           nwrite = write (output, outbuf,
                           (outp - outbuf) * sizeof (wchar_t));
           if (nwrite &lt; 0)
             {
               perror ("write");
               return 0;
             }
     
           /* <span class="roman">See if we have a </span><em>real</em><span class="roman"> invalid character.</span> */
           if ((eof &amp;&amp; filled &gt; 0) || filled &gt;= MB_CUR_MAX)
             {
               error (0, 0, "invalid multibyte character");
               return 0;
             }
     
           /* <span class="roman">If any characters must be carried forward,</span>
              <span class="roman">put them at the beginning of </span><code>buffer</code><span class="roman">.</span> */
           if (filled &gt; 0)
             memmove (buffer, inp, filled);
         }
     
       return 1;
     }
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