Re: [xml] question about getting numbers out of an xml file

[Daniel Veillard <veillard redhat com>]

On Sun, Mar 18, 2007 at 12:55:14AM -0400, Stefan Jeglinski wrote:
> I've been looking through the archives, and reading the API, and I'm 
> curious about something that must be a simple thing.
>
> I am using a small xml file to store some numbers (ints and floats). 
> I am trying to use an xpath to extract them.
>
> So, I started this way (sort of pseudo C code):
>
> doc      = xmlParseFile(filename);
> xpathCtx = xmlXPathNewContext(doc);
> xpath    = "/path/to/element";
> xpathObj = xmlXPathEvalExpression(xpathExpr, xpathCtx);
> content  = xmlNodeGetContent(xpathObj->nodesetval->nodeTab[0]);
>
> This gives me the content of the element as an xmlChar* (it works - 
> if it shouldn't then I made a typo). Of course since the element 
> content is to be used as a number (int, float) then I have to further 
> convert it from a string to a number.
>
> So, looking for something more elegant, I came across the function:
>
>       xmlXPathCastToNumber(xpathObj)
>
> This works fine returning a double. But I also came across the function:
>
>       xmlXPathStringEvalNumber(xpathObj->stringval);
>               or
>       xmlXPathStringEvalNumber(xpathObj->floatval);

  Wrong approach ... using the semi-internals functions of XPath module
to do the work instead of using XPath to do the extraction in a portable
way is really not 'elegant' from my point of view
  see 
    http://www.w3.org/TR/xpath#numbers
  and
    http://www.w3.org/TR/xpath#function-number

  something like xpath="number(/path/to/element)"
The evaluation will bring back a number , i.e. the xpathObj will be 
different but you will get the float directly.

Daniel

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