Re: Why do I need to overload =

From:

John Doe <mosfet@anonymous.org>

Newsgroups:

comp.lang.c++

Date:

Tue, 07 Oct 2008 16:22:14 +0200

Message-ID:

<48eb7097$0$11233$426a34cc@news.free.fr>

Victor Bazarov wrote:

John Doe wrote:

I am trying to transform a class with some time consuming operation by
adding a thread. To be able to pass data to thread I have declared a
class ThreadParam as shown below :
[..]
    struct ThreadParam
    {
        ThreadParam(CProvisioning* a_pThis, const CString&
a_strConfig, CString& a_strXmlOut):
            pThis(a_pThis),
            strConfig( a_strConfig ),
            strOut( a_strXmlOut ) {}

        CProvisioning* pThis;
        const CString& strConfig;
        CString& strOut;
    };
[...]

The problem I get is with m_thrParam = ThreadParam(this, strConfig,
strXmlOut); because I get :

error C2582: 'operator =' function is unavailable in
'CProvisioning::ThreadParam'

1) First I don't understand why I need to overload =

The compiler cannot generate one because you have reference members.
Once initialised (during construction), a reference cannot be reseated.

2) How can I fix it ?

You need to overload the assignment operator and decide what to do with
the 'strConfig' member (e.g. leave it alone) and the 'strOut' member.
*An example* of your operator= might look like this:

    struct ThreadParam
    {
        ...
        ThreadParam& operator=(ThreadParam const& other)
        {
            pThis = other.pThis;
            return *this;
        }
    };

V

The problem is once I run :

m_thrParam = ThreadParam(this, strConfig, strXmlOut);
strConfig is a valid reference but strXmlOut is NULL ...