Re: [xml] How to select a node based on attribute values?

[John Dennis <jdennis redhat com>]

On Tue, 2006-11-28 at 16:57 -0800, Yan Seiner wrote:
> Fist off, I'm a total newbie when it comes to libxml.  I've been able to 
> work my way through some examples, and produce working code, but I'm not 
> entirely happy with the result, and I would like some advice.
>
> I have an XML tree that looks like this:
>
> <root>
>     <plc id="1">
>        <some stuff/>
>     </plc>
>     <plc id="2">
>        <some other stuff/>
>     </plc>
> </root>
>
> I have a relatively small number (< 50) of the plc nodes, but the whole 
> tree is pretty big.
>
> What is the best (or simplest way) to retrieve the information for plc 2?

xpath is the simplest and most powerful

> Should I pull all of the plc elements using xmlXPathEvalExpression, and 
> then iterate over them with xmlGetProp looking for an id attribute with 
> a value of "2"?

no need to iterate, just create an xpath _expression_ which specifies id=2

off the top of my head the _expression_ would be "/plc[ id="2"]"

just google xpath syntax or xpath examples, you'll turn up a ton

libxml2 xpath example C code here: http://xmlsoft.org/examples/index.html#XPath

The xpath spec has examples too: http://www.w3.org/TR/xpath

If you're comfortable with python or another scripting language you can construct a simple test program to exercise your xpath syntax in about 5 minutes.

-- 
John Dennis <jdennis redhat com>