Re: the meaning of lvalue in C++

From:

"jam" <farid.mehrabi@gmail.com>

Newsgroups:

comp.std.c++

Date:

Fri, 9 Mar 2007 17:26:48 CST

Message-ID:

<1173474280.681252.159180@v33g2000cwv.googlegroups.com>

On Mar 10, 12:25 am, "restor" <akrze...@interia.pl> wrote:

Does lvalue have any useful meaning in C++? The original (i.e.: as
used in C) was that it is whatever that can be assigned a value. But
in C++ the code:

std::complex<double> Complex() { return std::complex<double>(); }
Complex() = Complex();

Is valid. Also the code:

int Integer() { return 1; }
const int& cref = Integer();
int& ref = const_cast<int&>( cref ); // is it a cast from rvalue to
lvalue???
ref = 3;

Is valid, but it is unclear (at least for me) what is 'ref'. Is it an
lvalue pointing to a temporary?
We also have non-modifiable lvalues (consts) and modifiable rvalues
like here:

ReturnObj().ModifyMe();

So what is useful in having a concept of lvalue in C++?

What is the use of an lvalue by the way?
I should say that even const objects can be lvalue:

struct Lvalue{
     Lvalue operator=(const Lvalue &)const{};//look at this!!
};

{
  const Lvalue L1,L2;
  L1=L2;//huh huh look at me
};

generally the only real Rvalue in C++ are literal numbers and
enumerations.

Have fun
FM

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