Re: How to get rid of VC warning C4239?

ZHENG Zhong <>
Fri, 6 Jul 2007 13:13:20 CST
On Jul 6, 3:32 pm, Ron Natalie <> wrote:

The warning is only benign in broken compilers like VC. Your program
is ill-formed (hence NOT C++). You can not bind rvalues to non-const

Further, all the things you are trying to do to stop the underlying
pimpl from being inappropriately modified is lost, so I'm not sure
what you think you are trying to accomplish.

Thank you for the reply. I think the first choice won't work for me,
since it breaks my xml API (i will explain it later). The second
choice... sorry but i did not understand what you wanted to tell me...
I think the current impl's copy semantics is already to copy the PIMPL
(what they do is to copy the boost::shared_ptr object, which is the

For the first choice... One of the goal of the basic_xml_node class
template is to make the interface pointer-free. For example, i have a
MsxmlNode class that uses msxml, and a LibxmlNode that uses libxml.
Both classes implement a member function called parent, like this:

class LibxmlNode {
    LibxmlNode* parent();

class MsxmlNode {
    MsxmlNode* parent();

Thus in my basic_xml_node class template, i implement the parent()
function to hide pointers (the memory management is implemented by the
library, and client don't need to worry about that).

template<class XmlNode>
class basic_xml_node {

    typedef basic_xml_node<XmlNode> node_type;

    explicit basic_xml_node(XmlNode* pimpl): pimpl_(pimpl) { }

    node_type parent() {
        XmlNode* px = pimpl_->parent();
        return node_type(px);

    XmlNode* pimpl_;

Thus, getting the parent node from one node is trivial:

typedef basic_xml_node<LibxmlNode> xml_node; // or, use MsxmlNode
xml_node child = ...;
xml_node parent = child.parent();

I want to keep the API trivial to use, and to disallow client code to
operate directly on pointers. But unfortunately, such implementation
requires that my basic_xml_node is "copyable" (in auto_ptr style).

Any help will be appreciated!


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