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<h1> pcb-rnd - plugin development - plugin cookie </h1>
<p>
Many of the pcb-rnd infrastructure API requires a <i>cookie</i> for
registering new objects. This cookie is typically a const char *, which
is used only in pointer comparison. It is also useful for debugging:
when objects are not unregistered properly, the code can print the value
(string) of the cookie in the error message, which can be a hint on the
source of the registration.
<p>
The cookie should be a <i>static const char</i> string, normally on top
of the main c file of the plugin:
<pre>
static const char *<i>pluginname</i>_cookie = "<i>pluginname</i> + a 2..3 word description";
</pre>
<h2> multiple cookies </h2>
<p>
The plugin may use multiple cookies, e.g. different cookie for registering
different set of objects, if that potentially helps debugging. This is especially
useful if the plugin is consists of largely independent subsystems - each
subsystem can have its own cookie.
<h2> multiple source files vs. cookies </h2>
<p>
If the plugin contains multiple compilation units (object files), these files
may need to use the same cookie. In that case <i>pluginname</i>_cookie
should not be static and shall be exposed in a plugin header file using
<i>extern</i>.
<p>
Since cookies are used by pointer, it is important <b>not to copy</b> the
string into multiple objects - those copies will not match. This can happen
accidentally on some systems if the header is missing <i>extern</i>.
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