Hi everyone,
I get the following error when compiling my code:
error: invalid initialization of non-const reference of type 'Vertex&'
from a temporary of type 'int'
The implementation of the function is as follows:
Vertex& IGEdge::Mate (Vertex const& vertex) {
if (v0 == vertex) {
return v1;
} else {
return 0;
}
}
What do you suggest to do? And why can't I return a simple
NULL-Pointer? All I want to do is to return a NULL in case my vertex v0
does not match the vertex being passed as a parameter.
Thanks a lot in advance,
CQ. 9 24169
CQ wrote: I get the following error when compiling my code:
error: invalid initialization of non-const reference of type 'Vertex&' from a temporary of type 'int'
The implementation of the function is as follows:
Let's simplify:
Vertex& IGEdge::Mate (Vertex const& vertex) { return 0;
What would that accomplish? There are no "null references" in C++.
}
What do you suggest to do? And why can't I return a simple NULL-Pointer?
Who says you can't? Please, by all means, do return a null *pointer*.
What you're trying to return is a "null reference" which doesn't exist.
All I want to do is to return a NULL in case my vertex v0 does not match the vertex being passed as a parameter.
Fine. But in that case your return type has to be a _pointer_, not
a _reference_.
V
> Who says you can't? Please, by all means, do return a null *pointer*. What you're trying to return is a "null reference" which doesn't exist.
But how do I create a null *pointer* that I can return? Is there a
construct in C++ that I can use?
Thanx,
CQ.
CQ wrote: Who says you can't? Please, by all means, do return a null *pointer*. What you're trying to return is a "null reference" which doesn't exist.
But how do I create a null *pointer* that I can return? Is there a construct in C++ that I can use? ...
You have to decide what is it you want to return. Your code is written
as if you want to return a _reference_. Now you are talking about
returning a _pointer_. So, what is it? Make up your mind. Pointers and
references are different things.
--
Best regards,
Andrey Tarasevich
Either change the call to actually reaturn a *POINTER*, which you
currently aren't doing, you are returning a *REFERENCE*. The other
error being, you are trying to uprade ( or downgrade, I forget what
they call it ) your type to be non-const. If you pass in a const
reference, you can't return a pointer to it that is not const. ( Well
you can, with a little extra magic, but you shouldn't )
Ex. 1
// This will do what you want, if you wat a pointer
const Vertex* IGEdge::Mate (Vertex const& vertex) {
if (v0 == vertex) {
return & v1;
} else {
return 0;
}
}
Ex. 2
// This is what returning a null reference looks like, see if you can
find whats wrong
Vertex& IGEdge::Mate (Vertex const& vertex) {
if (v0 == vertex) {
return v1;
} else {
return * (Vertex * ) 0; // I hope you see whats wrong
with this!!
}
}
CQ wrote: Who says you can't? Please, by all means, do return a null *pointer*. What you're trying to return is a "null reference" which doesn't exist.
But how do I create a null *pointer* that I can return? Is there a construct in C++ that I can use?
In the future versions there will be a separate keyword, but for now 0
should suffice. Make sure that the return value type is a pointer.
V
CQ wrote: Who says you can't? Please, by all means, do return a null *pointer*. What you're trying to return is a "null reference" which doesn't exist.
But how do I create a null *pointer* that I can return? Is there a construct in C++ that I can use?
Yes. Make the return type a Vertex* instead of a Vertex&, i.e. a *pointer*
instead of a *reference*.
Victor Bazarov wrote: But how do I create a null *pointer* that I can return? Is there a construct in C++ that I can use?
In the future versions there will be a separate keyword, but for now 0 should suffice. Make sure that the return value type is a pointer.
that's interesting. any references on this?
Aleksey Loginov wrote: Victor Bazarov wrote: But how do I create a null *pointer* that I can return? Is there a construct in C++ that I can use?
In the future versions there will be a separate keyword, but for now 0 should suffice. Make sure that the return value type is a pointer.
that's interesting. any references on this?
what a nice day :) found by myself http://open-std.org/jtc1/sc22/wg21/d...2003/n1488.pdf
"CQ" <su*******@gmx. net> wrote in message
news:11******** **************@ g44g2000cwa.goo glegroups.com.. . Hi everyone,
I get the following error when compiling my code:
error: invalid initialization of non-const reference of type 'Vertex&' from a temporary of type 'int'
The implementation of the function is as follows:
Vertex& IGEdge::Mate (Vertex const& vertex) { if (v0 == vertex) { return v1; } else { return 0; } }
What do you suggest to do? And why can't I return a simple NULL-Pointer? All I want to do is to return a NULL in case my vertex v0 does not match the vertex being passed as a parameter.
First suggestion, change it to return a pointer instead of a reference.
If you absolutely must return a reference (don't know why) perhaps return a
structure.
struct IGEdgeReturn
{
bool Good;
Vertex& Value;
}
and return that, seting Value to whatever, just ignore it in code if it's
not .good
I'm not saying you should do this, just saying you can. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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