Re: [Boost-users] [bind] Unable to pass method to simple function pointer

28 Oct 2009

      AMDG

Carlos wrote:
...
I am trying to make a wrapper for libxml's SAX api, for learning purpose, I
am trying to use bind to wrap sax events in a class like this :
namespace sax {
    class document {
public:
            document();
            ~document();
protected:
virtual void start_node( void *user_data, const xmlChar *name,
const xmlChar **attrs );
xmlSAXHandler m_evhdl;
            xmlParserCtxtPtr m_ctxt;
    };
}
The start_node() function is intended to be pointed by the startElement
member from xmlSAXHandler ( it has same definition than start_node ).
I tried to use bind to copy function pointer in the constructor like this :
document::document() {
// binding here
    m_evhdl.startElement = boost::bind( &document::start_node, this, _1, _2,
_3 );
// xml init
    m_ctxt = xmlCreateFileParserCtxt( "catalogue.xml" );
m_ctxt->sax = &m_evhdl;
    xmlParseDocument( m_ctxt );
}
The issue is that I can't submit the binded function to startElement because
bind submits "this" as a parameter to startElement, which is incompatible
definition, so is there a solution to my binding ?
I don't know much about libxml, but it looks like you should
pass the this pointer in the user_data argument of start_node.

Something like this:

class document {
    // ...
    static void start_node_func(void* user_data, const xmlChar* name, 
const xmlChar** attrs) {
        static_cast<document*>(user_data)->start_node(name, attrs);
    }
};

In Christ,
Steven Watanabe