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

• API Reference
• MDC - XPCOM
• IBM - An introduction to XPCOM
• Wikipedia - XPCOM
• MozillaZine - File IO Sample
• LXR - nsFileInputStream.h

Examples

nsFileInputStream on LXR Sample code for XPCOM component

 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 };

Sample use of XPCOM component

var fstream = Components.classes["@mozilla.org/network/file-input-stream;1"]
                        .createInstance(Components.interfaces.nsIFileInputStream);