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<h4 class="subsection">12.12.6 Other Output Conversions</h4>

<p>This section describes miscellaneous conversions for <code>printf</code>.

   <p>The &lsquo;<samp><span class="samp">%c</span></samp>&rsquo; conversion prints a single character.  In case there is no
&lsquo;<samp><span class="samp">l</span></samp>&rsquo; modifier the <code>int</code> argument is first converted to an
<code>unsigned char</code>.  Then, if used in a wide stream function, the
character is converted into the corresponding wide character.  The
&lsquo;<samp><span class="samp">-</span></samp>&rsquo; flag can be used to specify left-justification in the field,
but no other flags are defined, and no precision or type modifier can be
given.  For example:

<pre class="smallexample">     printf ("%c%c%c%c%c", 'h', 'e', 'l', 'l', 'o');
</pre>
   <p class="noindent">prints &lsquo;<samp><span class="samp">hello</span></samp>&rsquo;.

   <p>If there is a &lsquo;<samp><span class="samp">l</span></samp>&rsquo; modifier present the argument is expected to be
of type <code>wint_t</code>.  If used in a multibyte function the wide
character is converted into a multibyte character before being added to
the output.  In this case more than one output byte can be produced.

   <p>The &lsquo;<samp><span class="samp">%s</span></samp>&rsquo; conversion prints a string.  If no &lsquo;<samp><span class="samp">l</span></samp>&rsquo; modifier is
present the corresponding argument must be of type <code>char *</code> (or
<code>const char *</code>).  If used in a wide stream function the string is
first converted in a wide character string.  A precision can be
specified to indicate the maximum number of characters to write;
otherwise characters in the string up to but not including the
terminating null character are written to the output stream.  The
&lsquo;<samp><span class="samp">-</span></samp>&rsquo; flag can be used to specify left-justification in the field,
but no other flags or type modifiers are defined for this conversion. 
For example:

<pre class="smallexample">     printf ("%3s%-6s", "no", "where");
</pre>
   <p class="noindent">prints &lsquo;<samp><span class="samp"> nowhere </span></samp>&rsquo;.

   <p>If there is a &lsquo;<samp><span class="samp">l</span></samp>&rsquo; modifier present the argument is expected to be of type <code>wchar_t</code> (or <code>const wchar_t *</code>).

   <p>If you accidentally pass a null pointer as the argument for a &lsquo;<samp><span class="samp">%s</span></samp>&rsquo;
conversion, the GNU library prints it as &lsquo;<samp><span class="samp">(null)</span></samp>&rsquo;.  We think this
is more useful than crashing.  But it's not good practice to pass a null
argument intentionally.

   <p>The &lsquo;<samp><span class="samp">%m</span></samp>&rsquo; conversion prints the string corresponding to the error
code in <code>errno</code>.  See <a href="Error-Messages.html#Error-Messages">Error Messages</a>.  Thus:

<pre class="smallexample">     fprintf (stderr, "can't open `%s': %m\n", filename);
</pre>
   <p class="noindent">is equivalent to:

<pre class="smallexample">     fprintf (stderr, "can't open `%s': %s\n", filename, strerror (errno));
</pre>
   <p class="noindent">The &lsquo;<samp><span class="samp">%m</span></samp>&rsquo; conversion is a GNU C library extension.

   <p>The &lsquo;<samp><span class="samp">%p</span></samp>&rsquo; conversion prints a pointer value.  The corresponding
argument must be of type <code>void *</code>.  In practice, you can use any
type of pointer.

   <p>In the GNU system, non-null pointers are printed as unsigned integers,
as if a &lsquo;<samp><span class="samp">%#x</span></samp>&rsquo; conversion were used.  Null pointers print as
&lsquo;<samp><span class="samp">(nil)</span></samp>&rsquo;.  (Pointers might print differently in other systems.)

   <p>For example:

<pre class="smallexample">     printf ("%p", "testing");
</pre>
   <p class="noindent">prints &lsquo;<samp><span class="samp">0x</span></samp>&rsquo; followed by a hexadecimal number&mdash;the address of the
string constant <code>"testing"</code>.  It does not print the word
&lsquo;<samp><span class="samp">testing</span></samp>&rsquo;.

   <p>You can supply the &lsquo;<samp><span class="samp">-</span></samp>&rsquo; flag with the &lsquo;<samp><span class="samp">%p</span></samp>&rsquo; conversion to
specify left-justification, but no other flags, precision, or type
modifiers are defined.

   <p>The &lsquo;<samp><span class="samp">%n</span></samp>&rsquo; conversion is unlike any of the other output conversions. 
It uses an argument which must be a pointer to an <code>int</code>, but
instead of printing anything it stores the number of characters printed
so far by this call at that location.  The &lsquo;<samp><span class="samp">h</span></samp>&rsquo; and &lsquo;<samp><span class="samp">l</span></samp>&rsquo; type
modifiers are permitted to specify that the argument is of type
<code>short int *</code> or <code>long int *</code> instead of <code>int *</code>, but no
flags, field width, or precision are permitted.

   <p>For example,

<pre class="smallexample">     int nchar;
     printf ("%d %s%n\n", 3, "bears", &amp;nchar);
</pre>
   <p class="noindent">prints:

<pre class="smallexample">     3 bears
</pre>
   <p class="noindent">and sets <code>nchar</code> to <code>7</code>, because &lsquo;<samp><span class="samp">3 bears</span></samp>&rsquo; is seven
characters.

   <p>The &lsquo;<samp><span class="samp">%%</span></samp>&rsquo; conversion prints a literal &lsquo;<samp><span class="samp">%</span></samp>&rsquo; character.  This
conversion doesn't use an argument, and no flags, field width,
precision, or type modifiers are permitted.

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