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<h5 class="subsubsection">3.9.3.1 Inept excess verbiage</h5>

<p>Although the author of a library function may take pride in putting
its activities on display, it should be assumed that virtual code
applications running on <code>avram</code> have other agendas for the
console, so the library interface module should prevent direct output
from the external library.

   <p>More thoughtful API's may have a verbosity setting, which should be
<a name="index-verbosity-setting-677"></a>used in preference to this workaround, but failing that, it is easy to
dispense with console output generated by calls to external library
functions by using some combination of the following functions.

<div class="defun">
&mdash; Function: void <b>avm_turn_off_stdout</b> ()<var><a name="index-avm_005fturn_005foff_005fstdout-678"></a></var><br>
<blockquote><p>Calling this function will suppress all output to the standard output
stream until the next time <code>avm_turn_on_stdout</code> is called. 
Additional calls to this function without intervening calls to
<code>avm_turn_on_stdout</code> may be made safely with no effect.  The
standard output stream is flushed as a side effect of calling this
function. 
</p></blockquote></div>

<div class="defun">
&mdash; Function: void <b>avm_turn_on_stdout</b> ()<var><a name="index-avm_005fturn_005fon_005fstdout-679"></a></var><br>
<blockquote><p>Calling this function will allow output to the standard output
stream to resume if it has been suppressed previously by a call to
<code>avm_turn_off_stdout</code>. If <code>avm_turn_off_stdout</code> has not been
previously called, this function has no effect. Any output that would
have been sent to <code>stdout</code> during the time it was turned off will
be lost. 
</p></blockquote></div>

<div class="defun">
&mdash; Function: void <b>avm_turn_off_stderr</b> ()<var><a name="index-avm_005fturn_005foff_005fstderr-680"></a></var><br>
<blockquote><p>This function performs a similar service to that of
<code>avm_turn_off_stdout</code> but pertains to the standard error stream. 
The standard error and the standard output streams are controlled
independently even if both of them are piped to the same console. 
</p></blockquote></div>

<div class="defun">
&mdash; Function: void <b>avm_turn_on_stderr</b> ()<var><a name="index-avm_005fturn_005fon_005fstderr-681"></a></var><br>
<blockquote><p>This function performs a similar service to that of
<code>avm_turn_on_stdout</code> but pertains to the standard error stream. 
</p></blockquote></div>

   <p>As an example, the following code fragment will prevent any output to
standard output taking place as a side effect of <code>blather</code>, but
will allow error messages to standard error. Note that ouput should
not be left permanently turned off.

<pre class="example">     ...
     #include &lt;avm/mwrap.h&gt;
     ...
     
     x = y + z;
     avm_turn_off_stdout ();
     w = blather (foo, bar, baz);
     avm_turn_on_stdout ();
     return w;
     ...
</pre>
   <p>One possible issue with these functions is that they rely on a
feature of the GNU C library that might not be portable to non-GNU
<a name="index-portability-682"></a>systems and has not been widely tested on other platforms.

   <p>Another issue is that a library function could be both careless enough
to clutter the console unconditionally and meticulous enough to check
for I/O errors after each attempted write. Writing while the output
stream is disabled will return an I/O error to the caller (i.e., to
the verbose library function) for appropriate action, which could
include terminating the process.

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