Does not compile

[parag_paul]

#include <iostream>
using namespace std;

void ha(int& j);

void ha(int& j) {
cout <<j<<endl;
}
main()
{
int j = 0;
ha(NULL);
}
Why so ,
gcc version 3.3.6
p236.cc: In function `int main()':
p236.cc:14: error: invalid initialization of non-const reference of
type 'int&'
from a temporary of type 'long int'
p236.cc:6: error: in passing argument 1 of `void ha(int

[red floyd]

pa********@hotmail.com wrote:

#include <iostream>
using namespace std;

void ha(int& j);

void ha(int& j) {
cout <<j<<endl;
}
main()
{
int j = 0;
ha(NULL);
}
Why so ,
gcc version 3.3.6
p236.cc: In function `int main()':
p236.cc:14: error: invalid initialization of non-const reference of
type 'int&'
from a temporary of type 'long int'
p236.cc:6: error: in passing argument 1 of `void ha(int

Because NULL aka 0 is not an lvalue, it's an rvalue. There is no
variable to "refer" to. If ha() too a const int& as a param, then you
could bind it to the temporary (created by the call).

Or are you working on the assumption that a reference is a pointer, and
you're trying to create a NULL reference?

In that case, please repeat after me: A REFERENCE IS NOT A POINTER.
It may be (and probably *is*) implemented as such, but an implementation
is not required to do so.

[Ian Collins]

pa********@hotmail.com wrote:

On Nov 2, 12:32 pm, Andrey Tarasevich <[e-mail]>
wrote:

>It is worth noting though, that NULL macro should normally be used in
pointer context and using it in place of an 'int' value is not a good
practice.

*Please* don't quote signatures.

>
That helps thanks a lot.
I did not get the NULL macro.
Where is it defined?

It can be defined in a number of places (probably for historical
reasons), the standard lists them in C 2.2.3. For your implementation,
you'll have to do a search.

--
Ian Collins.

[Victor Bazarov]

pa********@hotmail.com wrote:

[..]
I did not get the NULL macro.
Where is it defined?

<cstdlib>

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

[Shadowman]

Victor Bazarov wrote:

Shadowman wrote:

>pa********@hotmail.com wrote:

>>That helps thanks a lot.
I did not get the NULL macro.
Where is it defined?

I've found it in several header files as:

#define NULL 0

or

#define NULL ((void*)0)

The latter is not legal in C++ because it is not an "integral constant
expression of value 0".

OK, sorry, I must have been looking in C library headers...

--
SM
rot13 for email

[James Kanze]

On Nov 2, 9:39 pm, Ian Collins <[e-mail]:

[e-mail] wrote:

On Nov 2, 12:32 pm, Andrey Tarasevich <[e-mail]>
wrote:

It is worth noting though, that NULL macro should normally be used in
pointer context and using it in place of an 'int' value is not a good
practice.

That helps thanks a lot.
I did not get the NULL macro.
Where is it defined?

It can be defined in a number of places (probably for
historical reasons), the standard lists them in C 2.2.3. For
your implementation, you'll have to do a search.

It must be defined in all of those places, according to the
standard. Or more correctly, it must be defined after you have
included any of those headers.

The usual header, if you just want NULL, is <cstddef>.

--
James Kanze (GABI Software) email:ja*********@gmail.com
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