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Writing rules: Minor updates. Trying to make it easier.

This commit is contained in:
Daniel Marjamäki 2010-12-05 13:19:30 +01:00
parent eaea572683
commit 68f2c47c5c
1 changed files with 36 additions and 24 deletions
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60
man/writing-rules.docbook
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@ -118,7 +118,8 @@
<section>
<title>Regular expressions</title>
<para>Simple rules can be defined through regular expressions.</para>
<para>Simple rules can be defined through regular expressions. Cppcheck
uses PCRE to handle regular expressions.</para>
<section>
<title>Creating regular expression</title>
@ -128,35 +129,42 @@
<programlisting>if (p)
free(p);</programlisting>
<para>The condition is often redundant, it is valid to free a NULL
pointer.</para>
<para>The condition is often redundant, on most implementations it is
valid to free a NULL pointer.</para>
<para>It is important to write the regular expression so it matches the
simplified code. Create a source file that has the bad code:</para>
<para>The regular expression must match the simplified code. Create a
source file that has the bad code:</para>
<programlisting>void f() {
if (p) free(p);
if (p)
free(p);
}</programlisting>
<para>I intentionally put the whole pattern on a single line. The
simplified code is written on a single line of code.</para>
<para>To see the simplified code I use <literal>cppcheck --debug
file.cpp</literal>.</para>
<para>To see the simplified code use <literal>cppcheck --debug
dealloc.cpp</literal>.</para>
<programlisting>##file dealloc.cpp
1: void f ( ) {
2: if ( p ) { free ( p ) ; }
3: }</programlisting>
2: if ( p ) {
3: free ( p ) ; }
4: }</programlisting>
<para>I save that in a file <literal>test.txt</literal>.</para>
<para>In the <literal>--debug</literal> output there are line feeds and
line numbers. But the newlines and line numbers are only there to make
the output easier to read. The real simplified code is written on a
single line:</para>
<para>Now we can use <literal>grep</literal> to develop a regular
expression.</para>
<programlisting>void f ( ) { if ( p ) { free ( p ) ; } }</programlisting>
<programlisting>grep "if [(] p [)] { free [(] p [)] ; }" test.txt</programlisting>
<para>Now we can use <literal>cppcheck --rule</literal> to develop a
regular expression.</para>
<para>Feel free to improve the pattern.</para>
<programlisting>$ cppcheck --rule="if \( p \) { free \( p \) ; }" dealloc.cpp
Checking dealloc.cpp...
[dealloc.cpp:2]: (style) found 'if ( p ) { free ( p ) ; }'</programlisting>
<para>Feel free to improve the pattern. Above, the pointer name must be
"p" to get a match.</para>
</section>
<section>
@ -170,8 +178,8 @@
</listitem>
<listitem>
<para>an optional error message that is reported when pattern is
found</para>
<para>an error message that is reported when pattern is found - this
is optional, if none is given a default message is written.</para>
</listitem>
</itemizedlist>
@ -179,7 +187,7 @@
<programlisting>&lt;?xml version="1.0"?&gt;
&lt;rule version="1"&gt;
&lt;pattern&gt;if [(] p [)] { free [(] p [)] ; }&lt;/pattern&gt;
&lt;pattern&gt;if \( p \) { free \( p \) ; }&lt;/pattern&gt;
&lt;message&gt;
&lt;id&gt;redundantCondition&lt;/id&gt;
&lt;severity&gt;style&lt;/severity&gt;
@ -189,10 +197,14 @@
<para>The <literal>message</literal>, <literal>id</literal>,
<literal>severity</literal> and <literal>summary</literal> elements are
optional. If they are not written default values are used.</para>
optional. But highly recommended.</para>
<para>Now you can test this rule. Use the <literal>cppcheck
--rule-file=dealloc.rule test.cpp</literal> command.</para>
<para>If you save that xml data in <literal>dealloc.rule</literal> you
can test this rule:</para>
<programlisting>$ cppcheck --rule-file=dealloc.rule dealloc.cpp
Checking dealloc.cpp...
[dealloc.cpp:2]: (style) Redundant condition. It is valid to free a NULL pointer.</programlisting>
</section>
</section>
</article>