I wish to develop a simple plugin for QGIS, which will open some data, and perform some specific processing.
I tried searching on the QGIS wiki, but only found this link :
http://www.qgis.org/wiki/Writing_C++_Plugins
which seems to be obsolete. There were also a few blog posts from 2006.
I also saw something about Python plugins, but I am not sure whether I need to work with the C++ plugin or a Python plugin.
Where can I find documentation, or tutorials, that would help me get started?
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C++ plugins are less and less common these days. Most likely because they are more difficult to develop. Most documentation effort has been put into Python plugins. C++ still has it's place for performance critical things and functionality that is supposed to be merged into QGIS core (like new renderers for example).
There is a Plugin builder plugin which helps to create the basic plugin structure for you.
The PyQGIS Cookbook offers a lot of code snippets for Python plugins
The book PyQGIS Programmer's Guide is another good resource.
If you get stuck, the QGIS developer mailing list is there to help you.
Basically you need to know 3 things:
They are all very well documented, to get started I recommend you to browse through the modules of the QGIS API and play with the python console doing basic things like accessing the features of a vector layer.
Later, after you get the feel of the api, you can ask more specific questions here on GIS SE e.g. Using QGIS API and Python, to return latitude and longitude of point?
