View source for XPCOM

Paul St-Denis & Michael Lau

= Short Description =
XPCOM stands for Cross Platform Component Object Model. XPCOM is a framework for developing cross platform software.

= Detailed Discussion =
XPCOM is a framework for developing cross platform software that can be written in C, C++, JavaScript with extensions for Perl and Python.  It supports any platform with a C++ compiler.  


You can access the XPCOM component through the web or any Mozilla application (similar to the idea of accessing web services).


Some of the tools needed for development are:
* a C++ compiler
* a Perl interpreter
* some GNU tools


XPCOM provides the following features for cross platform development:
* Component management
* File abstraction
* Object message passing
* Memory management


Application that want to access Mozilla XPCOM libraries can use an XPCOM layer called XPConnect.

= External Links =
*[http://developer.mozilla.org/en/docs/XPCOM_API_Reference#Overview API Reference]
*[http://developer.mozilla.org/en/docs/XPCOM MDC - XPCOM]
*[http://www-128.ibm.com/developerworks/webservices/library/co-xpcom.html IBM - An introduction to XPCOM]
*[http://en.wikipedia.org/wiki/XPCOM Wikipedia - XPCOM]
*[http://kb.mozillazine.org/File_IO MozillaZine - File IO Sample]
*[http://lxr.mozilla.org/seamonkey/source/netwerk/base/src/nsFileStreams.h#77 LXR - nsFileInputStream.h]

= Examples =
[http://lxr.mozilla.org/seamonkey/source/netwerk/base/src/nsFileStreams.h#77 nsFileInputStream on LXR] Sample code for XPCOM component
<pre>
 77 class nsFileInputStream : public nsFileStream,
 78                           public nsIFileInputStream,
 79                           public nsILineInputStream
 80 {
 81 public:
 82     NS_DECL_ISUPPORTS_INHERITED
 83     NS_DECL_NSIINPUTSTREAM
 84     NS_DECL_NSIFILEINPUTSTREAM
 85     NS_DECL_NSILINEINPUTSTREAM
 86     
 87     // Overrided from nsFileStream
 88     NS_IMETHOD Seek(PRInt32 aWhence, PRInt64 aOffset);
 89 
 90     nsFileInputStream() : nsFileStream() 
 91     {
 92         mLineBuffer = nsnull;
 93         mBehaviorFlags = 0;
 94     }
 95     virtual ~nsFileInputStream() 
 96     {
 97         Close();
 98     }
...
135     nsresult Reopen() { return Open(mFile, mIOFlags, mPerm); }
136 };
</pre>

[http://kb.mozillazine.org/File_IO Sample use of XPCOM component]
<pre>
var fstream = Components.classes["@mozilla.org/network/file-input-stream;1"]
                        .createInstance(Components.interfaces.nsIFileInputStream);
</pre>