Re: std::vector and object errors

From:

"Benry" <henrybg@gmail.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

30 May 2006 08:35:00 -0700

Message-ID:

<1149003300.073647.294270@u72g2000cwu.googlegroups.com>

David Wilkinson wrote:

Benry wrote:

David Webber wrote:

"Benry" <henrybg@gmail.com> wrote in message
news:1148998543.357718.323440@y43g2000cwc.googlegroups.com...

I'm using a vector object in my code.

(from MyType.h)
std::vector<CMyType> m_vMyType;

c:\program files\microsoft visual studio\vc98\include\xutility(19) :
error C2679: binary '=' : no operator defined which takes a right-hand
operand of type 'const class CMyType' (or there is no acceptable
conversion)

You need to supply an assignment operator - typically of the form

CMyType & CMyType::operator = ( const CMyType &x )
{
............
}

I do.
CMyType CMyType::operator=( CMyType &other ) {
    //vector <int> v4( v2 );
    std::vector <CString>::iterator v_Iter;
    for ( v_Iter = other.vFields.begin( ) ; v_Iter != other.vFields.end( )
; v_Iter++ ){
        this->vFields.push_back( *v_Iter );
    }
    this->sTableName = other.sTableName;
    return *this;
}

c:\program files\microsoft visual studio\vc98\include\xmemory(34) :
error C2558: class 'CMyType' : no copy constructor available

and a copy constructor

CMyType::CMyType( const CMyType &x )
{
.........
}

I do that too.

CMyType:: CMyType( CMyType &rhs)
{
    std::vector <CString>::iterator v_Iter;
    for ( v_Iter = rhs.vFields.begin( ) ; v_Iter != rhs.vFields.end( ) ;
v_Iter++ ){
        vFields.push_back( *v_Iter );
    }
    sTableName = rhs.sTableName;
}

Perhaps it's because I'm not using const? (five minute pause)...ok I
changed it to const, and now am having a problem with the vector
assignment loop. Perhaps if this is fixed? Could you recommend
something to fix the vector copying?

Forget it, I took out the loop, and just used the std::vector equals
operator, and it works now. Thanks for the hint!!

-Benry

Benry:

1. Assignment operator and copy constructor should always take a const
reference argument; otherwise you cannot copy a constant object. The
correct syntax is as given by David Webber.

Fixed, and will note for the future.

2. In your posted code, why are you creating tjtemp on the heap? You are
storing objects in your vector, not pointers. Surely your code is
leaking memory?

I am deleting the pointer after it's being used, so there are no leaks.
I'm using new because of the constructor, and it's been that way since
I started? I don't know I guess.

3. It is not clear why you need to specify your own assignment operator
and copy constructor here. Doesn't the default one (member-wise copy) do
what you want?

There are two error messages, and using my own assignment operator and
copy constructor are what was needed to fix the issue. My program
works now. Thank you.

-Benr

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