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<h4 class="subsection">12.22.3 How to use <code>fmtmsg</code> and <code>addseverity</code></h4>

<p>Here is a simple example program to illustrate the use of the both
functions described in this section.

<pre class="smallexample">     #include &lt;fmtmsg.h&gt;
     
     int
     main (void)
     {
       addseverity (5, "NOTE2");
       fmtmsg (MM_PRINT, "only1field", MM_INFO, "text2", "action2", "tag2");
       fmtmsg (MM_PRINT, "UX:cat", 5, "invalid syntax", "refer to manual",
               "UX:cat:001");
       fmtmsg (MM_PRINT, "label:foo", 6, "text", "action", "tag");
       return 0;
     }
</pre>
   <p>The second call to <code>fmtmsg</code> illustrates a use of this function as
it usually occurs on System V systems, which heavily use this function. 
It seems worthwhile to give a short explanation here of how this system
works on System V.  The value of the
<var>label</var> field (<code>UX:cat</code>) says that the error occurred in the
Unix program <code>cat</code>.  The explanation of the error follows and the
value for the <var>action</var> parameter is <code>"refer to manual"</code>.  One
could be more specific here, if necessary.  The <var>tag</var> field contains,
as proposed above, the value of the string given for the <var>label</var>
parameter, and additionally a unique ID (<code>001</code> in this case).  For
a GNU environment this string could contain a reference to the
corresponding node in the Info page for the program.

<p class="noindent">Running this program without specifying the <code>MSGVERB</code> and
<code>SEV_LEVEL</code> function produces the following output:

<pre class="smallexample">     UX:cat: NOTE2: invalid syntax
     TO FIX: refer to manual UX:cat:001
</pre>
   <p>We see the different fields of the message and how the extra glue (the
colons and the <code>TO FIX</code> string) are printed.  But only one of the
three calls to <code>fmtmsg</code> produced output.  The first call does not
print anything because the <var>label</var> parameter is not in the correct
form.  The string must contain two fields, separated by a colon
(see <a href="Printing-Formatted-Messages.html#Printing-Formatted-Messages">Printing Formatted Messages</a>).  The third <code>fmtmsg</code> call
produced no output since the class with the numeric value <code>6</code> is
not defined.  Although a class with numeric value <code>5</code> is also not
defined by default, the call to <code>addseverity</code> introduces it and
the second call to <code>fmtmsg</code> produces the above output.

   <p>When we change the environment of the program to contain
<code>SEV_LEVEL=XXX,6,NOTE</code> when running it we get a different result:

<pre class="smallexample">     UX:cat: NOTE2: invalid syntax
     TO FIX: refer to manual UX:cat:001
     label:foo: NOTE: text
     TO FIX: action tag
</pre>
   <p>Now the third call to <code>fmtmsg</code> produced some output and we see how
the string <code>NOTE</code> from the environment variable appears in the
message.

   <p>Now we can reduce the output by specifying which fields we are
interested in.  If we additionally set the environment variable
<code>MSGVERB</code> to the value <code>severity:label:action</code> we get the
following output:

<pre class="smallexample">     UX:cat: NOTE2
     TO FIX: refer to manual
     label:foo: NOTE
     TO FIX: action
</pre>
   <p class="noindent">I.e., the output produced by the <var>text</var> and the <var>tag</var> parameters
to <code>fmtmsg</code> vanished.  Please also note that now there is no colon
after the <code>NOTE</code> and <code>NOTE2</code> strings in the output.  This is
not necessary since there is no more output on this line because the text
is missing.

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