Re: [xml] Problems when using several free functions

[cbozeman hiwaay net]

Quoting Pinho external infineon com:

> Hi There,
>
>       First of all I'm new to the world of C and libxml, and due to my OO
> background (mainly JAVA) I don't master the ways of pointers, and I'm
> having
> a hard time to get some things right using libxml.
>
>       The program that I'm developing is using xPath in a massive way,
> it's a kind of XML document comparer, but, it doesn't care about the
> order
> of it's elements, so with xPath it's very easy to compare two elements
> even
> if thay have a different order in the XMLDocument.
>
>       To get this done I'm using xPath API and some structs from tree API
> like xmlDocPtr or xmlNode, etc...
>
>       The program reads a XML document string and then parse it's
> (xmlParseDoc(stringWithXmlDoc)), then, depending on the kind of
> structure
> that I find (simple, complex, array, etc) I do diferent things. 
>       I always use xmlXPathEvalExpression to get the node that I want and
> then use the returned node to compare the values and the inner structure
> of
> some xml elements to see if they are equal. To travel trough all the
> Xml
> document I use a recursive function. 
>
>       
>       I have 2 problems:
>
>       I wanted to initialize the context only once, outside that recursive
> function, and then call the recursive function, when I do this, at the
> 2nd
> or 3th level of recursion the xmlXPathEvalExpression returns null, just
> like
> the context changed, this is strange because I've done nothing to the
> context !?!? If I do the parsing of the string (call the xmlParseDoc
> function again) and then create the context at each recursive call
> it's
> works fine, if I try to initiate the context only once, I get the
> problem
> described. 
When an XPath expression is evaluated, the current node (ctxt->node) in the 
context is set to the result of the evaluation. Depending upon where you want 
your search to start from, you may need to reset the current node. In any case 
you should not have to reparse the document or create a new context.

>       Another problem that I'm having is when I use the functions to free
> the libxml objects, sometimes I get a invalid access error (before the
> call
> to the xmlFreeXXXX I test the variable to see if it's null). Is there
> another test I must do before calling the xmlFreeXXX functions? When
> must I
> call the function xmlFreeXXX, only when the API tells me to?
>
>
>
>
>
> Any help is very welcome,
>
>
> Thank You
>
> Luís Pinho
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