Pretty printing XML in wxWidgets

Question

I'm writing a class derived from wxStyledTextCtrl and I want it to prettify given XML without adding anything other than whitespaces. I cannot find simple working solution. I can only use wxStyledTextCtrl, wxXmlDocument and libxml2.

The result I'm aiming for is that after calling SetText with wxString containing following text

<!-- comment1 --> <!-- comment2 --> <node><emptynode/> <othernode>value</othernode></node>

the control should show

<!-- comment1 -->
<!-- comment2 -->
<node>
    <emptynode/>
    <othernode>value</othernode>
</node>

using libxml2 I managed to almost achieve this, but it also prints XML declaration (eg. <?xml version="1.0" encoding="UTF-8"?>) and I don't want this.

inb4, I'm looking for simple and clean solution - i don't want to manually remove first line of formatted XML

Is there any simple solution to this using given tools? I feel like I'm missing something.

Answer 1

Is there a simple solution? No. But if you want to write you're own pretty print function, you basically need to make a depth first iteration over the xml document tree, printing it as you go. There's a slight complication in that you also need some way of knowing when to close a tag.

Here's an incomplete example of one way to do this using only wxWidgets xml classes. Currently, it doesn't handle attributes, self closing elements (such as '' in your sample text), or any other special element types. A complete pretty printer would need to add those things.

#include <stack>
#include <set>
#include <wx/xml/xml.h>
#include <wx/sstream.h>

wxString PrettyPrint(const wxString& in)
{
    wxStringInputStream string_stream(in);
    wxXmlDocument doc(string_stream);
    wxString pretty_print;

    if (doc.IsOk())
    {
        std::stack<wxXmlNode*> nodes_in_progress;
        std::set<wxXmlNode*> visited_nodes;

        nodes_in_progress.push(doc.GetDocumentNode());

        while (!nodes_in_progress.empty())
        {
            wxXmlNode* cur_node = nodes_in_progress.top();
            nodes_in_progress.pop();
            int depth = cur_node->GetDepth();

            for (int i=1;i<depth;++i)
            {
                pretty_print << "\t";
            }

            if (visited_nodes.find(cur_node)!=visited_nodes.end())
            {
                pretty_print << "</" << cur_node->GetName() << ">\n";
            }
            else if ( !cur_node->GetNodeContent().IsEmpty() )
            {
                //If the node has content, just print it now
                pretty_print << "<" << cur_node->GetName() << ">";
                pretty_print << cur_node->GetNodeContent() ;
                pretty_print << "</" << cur_node->GetName() << ">\n";
            }
            else if (cur_node==doc.GetDocumentNode())
            {
                std::stack<wxXmlNode *> nodes_to_add;
                wxXmlNode *child = cur_node->GetChildren();
                while (child)
                {
                    nodes_to_add.push(child);
                    child = child->GetNext();
                }

                while (!nodes_to_add.empty())
                {
                    nodes_in_progress.push(nodes_to_add.top());
                    nodes_to_add.pop();
                }
            }
            else if (cur_node->GetType()==wxXML_COMMENT_NODE)
            {
                pretty_print << "<!-- " << cur_node->GetContent() << " -->\n";
            }
            //insert checks for other types of nodes with special
            //printing requirements here
            else
            {
                //otherwise, mark the node as visited and then put it back
                visited_nodes.insert(cur_node);
                nodes_in_progress.push(cur_node);

                //If we push the children in order, they'll be popped
                //in reverse order.
                std::stack<wxXmlNode *> nodes_to_add;
                wxXmlNode *child = cur_node->GetChildren();
                while (child)
                {
                    nodes_to_add.push(child);
                    child = child->GetNext();
                }

                while (!nodes_to_add.empty())
                {
                    nodes_in_progress.push(nodes_to_add.top());
                    nodes_to_add.pop();
                }

                pretty_print <<"<" << cur_node->GetName() << ">\n";
            }
        }
    }

    return pretty_print;
}