CODEWITHSUNDEEP
c++vector
Vinícius
Vinícius

Reputation: 15718

Why inserting an object into vector causes C2679

I'm sorry but there can't be an example so we'll have to take a look into the real code here. What happens is, I have class CItemElem (note this is an old source, please disconsider hungarian notations, class names etc..). As in the example below I'm trying to do the same with CItemElem

class A
{
public:
    int value;
};

int _tmain( int argc, _TCHAR* argv[] )
{
    std::vector<A> hold;
    A a;
    hold.push_back(a);
}

Althought with class CItemElem the compiler gives me C2679 when trying to

vector<CItemElem>hold; CItemElem item; hold.push_back(item);

Error C2679: '=' binary :no operator found which takes a right-hand operand of type 'const CItemElem' (or there is no acceptable conversion)

by clicking at the error it leads me to this line *_First = _Val; at this function on xutility

template<class _FwdIt,
    class _Ty> inline
    void fill(_FwdIt _First, _FwdIt _Last, const _Ty& _Val)
    {   // copy _Val through [_First, _Last)
    for (; _First != _Last; ++_First)
        *_First = _Val;
    }

The CItemElem class is too long and derived so I decided to upload it to pastebin, instead of pasting the huge code in here. Pastebin: Class CItemElem Header (item.h)

Note that CItemElem is derived from CItemBase and has = operator overloaded, which also passes throught CItemBase = operator. This is from item.cpp:

CItemElem& CItemElem::operator =( CItemElem & ie )
{
    CItemBase::operator =( ie );

Upvotes: 0

Views: 223

Answers (2)

Beta
Beta

Reputation: 99094

It looks as if there is no defined assignment operator (=) for CItemElem. The STL containers (e.g.vector) expect the things they contain to have certain properties, including an assignment operator. If you can modify the class, you can add one:

class CItemElem
{
...
public:

  CItemElem & operator=(const CItemElem &other)
  {
    // copy whatever must be copied
    x = other.x;

    return *this;
  }
}

EDIT:
I see now that the header includes a declaration of an assignment operator:

virtual CItemElem&      operator = ( CItemElem & ie );

but the signature is wrong-- it's missing const. If you can change this (in the declaration and the definition) it should work.

EDIT:
If you can't edit the base class, you have a couple of options. Probably the safest is to copy the code from CItemBase::operator= into CItemElem::operator=. It's not pretty, but that's the original author's fault; the argument should have been const & all along.

Upvotes: 3

Puppy
Puppy

Reputation: 146910

CItemElem has operator=(CItemElem&). This function cannot accept a const argument (as the compiler accurately told you) and does not meet the requirements of std::vector as an element type. It is impossible to use this class in a std::vector.

Upvotes: 2

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