[gmpi] Re: Linux C++ question
- To: <gmpi@xxxxxxxxxxxxx>
- Date: Wed, 23 Feb 2005 16:24:06 -0500
A few more stylistic nits:
[1] For in arguments, I like to use const references. Pointers are
reserved for out. That gives a very handy way of knowing, at the call
site, what might change and what might not. So:
GMPI_Factory::CreateInstance( const GMPI_GUID& iid, ... )
Note that a reference is the same as a pointer in C, or at least that's
how they do it in COM. They declare the interface as const GUID*, but
the impl can be const GUID&.
Another nit: when comparing values in an 'if', put the constant value
on the left side, not the right. So not this:
if (foo == 0)
but this:
if (0 == foo)
Why? If you accidentally type '=' instead of '==' the former can get
you in trouble if your compiler isn't strict. The latter will always
complain.
Lastly, I still like to use NULL instead of 0 for pointers. I know in
C++ you can use 0, but it's an old habit that helps reinforce that you
are dealing with a pointer.
By the way, those coding style survey results... are pretty
inconclusive. There really isn't a clear majority of one style vs.
another. I'm not sure what there is to tablulate.
PPS: I'm leaving tomorrow for vacation, back in the office next
Wednesday.
-----Original Message-----
From: gmpi-bounce@xxxxxxxxxxxxx [mailto:gmpi-bounce@xxxxxxxxxxxxx] On
Behalf Of Ron Kuper
Sent: Wednesday, February 23, 2005 4:17 PM
To: gmpi@xxxxxxxxxxxxx
Subject: [gmpi] Re: Linux C++ question
At what point in the exit sequence does it crash? Where in the DLL
specifically?
Also, could plugin_list be a map instead? That would avoid having to
iterate to lookup.
Lastly, is plugin_list a member of class GMPI_Factory? Pretty please,
m_plugin_list? :-)
-----Original Message-----
From: gmpi-bounce@xxxxxxxxxxxxx [mailto:gmpi-bounce@xxxxxxxxxxxxx] On
Behalf Of Jeff McClintock
Sent: Wednesday, February 23, 2005 4:14 PM
To: gmpi@xxxxxxxxxxxxx
Subject: [gmpi] Linux C++ question
A question for someone familier (very familier) with C++ on Linux.
A GMPI dll may contain several plugins. In the GMPI prototype. An
object called the factory maintains a list. There is only ever one
factory. I used a singleton to implement such. However Tim reports
that it crashes while unloading the dll. Any help appreciated.
details:
The technique comes from "Modern C++ Design - Andrei Alexandrescu",
author of the Loki library.
This is the essential code. Ignore the GMPIness of this...If you want
to see the entire file, let me know.
/* factory is a singleton, this retrieves a pointer to it */
GMPI_Factory *Factory(void)
{
static GMPI_Factory the_factory;
return &the_factory;
}
/* register a plugin with this factory */
GMPI_RESULT GMPI_Factory::RegisterPlugin( const GMPI_GUID *iid,
PLUGIN_CREATE_FUNCTION create_function )
{
plugin_list.push_back( pair<const GMPI_GUID
*,PLUGIN_CREATE_FUNCTION>(iid, create_function) );
return GMPI_SUCCESS;
}
/* Instantiate a GMPI_Plugin */
GMPI_RESULT GMPI_Factory::CreateInstance( GMPI_GUID *plugin_id, void
**object )
{
/* search plugin list for requested type */
for( list< pair<const GMPI_GUID *,PLUGIN_CREATE_FUNCTION>
>::iterator
it = plugin_list.begin() ; it != plugin_list.end() ; it++ )
{
if( GIMPI_IsEqualIID( plugin_id, (*it).first ) )
{
/* call plugin create function */
GMPI_Plugin *plugin = ((*it).second)();
if (plugin == 0)
{
*object = 0;
return GMPI_FAIL;// E_OUTOFMEMORY;
}
return plugin->QueryInterface( (GMPI_GUID *)
&IID_GMPI_IUnknown ,
object );
}
}
/* couln't find requested type, return error */
*object = 0;
return GMPI_FAIL;
}
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