Question is about the difference between these two
reference to an object versus pointer to an object
What are advantages in either one and when would one use them. I see
lots of examples when an object is passed as a parameter to a function
it is passed as a reference. Though it would have been fine to pass it
as a pointer as well ? is that right ?
I had posted a similar question in the C lang newsgroup but did not
get much help as C does not do references to objects. 20 4331
On 30 Jun 2004 21:06:34 -0700, m sergei <se********@yahoo.com> wrote: Question is about the difference between these two
reference to an object versus pointer to an object
What are advantages in either one and when would one use them. I see lots of examples when an object is passed as a parameter to a function it is passed as a reference. Though it would have been fine to pass it as a pointer as well ? is that right ?
It would work if passed as a pointer. But
1) A pointer can be NULL, so the function must test for that.
2) A pointer cannot be initialised with a temporary, so you lose
flexibility
X f();
void g(const X&);
g(f()); // fine
X f();
void g(const X*);
g(&f()); // compile error
I had posted a similar question in the C lang newsgroup but did not get much help as C does not do references to objects.
Not surprising really.
john
> 1) A pointer can be NULL, so the function must test for that. 2) A pointer cannot be initialised with a temporary, so you lose flexibility
and
3) A pointer can be indexed while a reference can not. So by using a
reference you implicit state that this is not an array.
4) The syntax for using a reference is the same as for using an object on
the stack, so it is easier to rewrite code that previously worked on a stack
object to use a reference than to use a pointer.
Niels Dybdahl
On Thu, 1 Jul 2004 10:23:06 +0200, "Niels Dybdahl"
<nd*@fjern.detteesko-graphics.com> wrote: and
3) A pointer can be indexed while a reference can not. So by using a reference you implicit state that this is not an array.
Not necessarily.
For references to built-in types, this is true. However, user-defined
types can overload operator[], and you can of course index a reference
to a pointer of any type. The mere fact that you have a reference
doesn't automatically prohibit the use of operator[] from the
standpoint of the grammar.
--
Bob Hairgrove No**********@Home.com
"Bob Hairgrove" <wouldnt_you_like@to_know.com> wrote in message
news:jd********************************@4ax.com... On Thu, 1 Jul 2004 10:23:06 +0200, "Niels Dybdahl" <nd*@fjern.detteesko-graphics.com> wrote:
and
3) A pointer can be indexed while a reference can not. So by using a reference you implicit state that this is not an array.
Not necessarily.
For references to built-in types, this is true. However, user-defined types can overload operator[], and you can of course index a reference to a pointer of any type. The mere fact that you have a reference doesn't automatically prohibit the use of operator[] from the standpoint of the grammar.
No, but if you have a type that defines operator[], using [] on a pointer to
it would index the pointer, while using it on a reference indexes the
original type. Using a pointer in such a scenario can lead to subtle bugs,
and at the very least ugly syntax such as (*somevar)[2].
--
Unforgiven
On Thu, 1 Jul 2004 11:35:28 +0200, "Unforgiven"
<ja*******@hotmail.com> wrote: "Bob Hairgrove" <wouldnt_you_like@to_know.com> wrote in message news:jd********************************@4ax.com.. . On Thu, 1 Jul 2004 10:23:06 +0200, "Niels Dybdahl" <nd*@fjern.detteesko-graphics.com> wrote:
and
3) A pointer can be indexed while a reference can not. So by using a reference you implicit state that this is not an array.
Not necessarily.
For references to built-in types, this is true. However, user-defined types can overload operator[], and you can of course index a reference to a pointer of any type. The mere fact that you have a reference doesn't automatically prohibit the use of operator[] from the standpoint of the grammar.
No, but if you have a type that defines operator[], using [] on a pointer to it would index the pointer, while using it on a reference indexes the original type. Using a pointer in such a scenario can lead to subtle bugs, and at the very least ugly syntax such as (*somevar)[2].
That's true, but that certainly wasn't what I was referring to. The
issue was whether one could index a reference or not. I wasn't talking
about indexing into a pointer, except in the context of reference to
pointer.
Yet another reason to use STL container classes and avoid arrays and
pointers if possible.
--
Bob Hairgrove No**********@Home.com
void g(const X&) why is const required ? is that a requirement to inform the
compiler ?
also your second function void g(const X*).
is void g(const *X) same as above ? (or correct ?) It would work if passed as a pointer. But
1) A pointer can be NULL, so the function must test for that.
2) A pointer cannot be initialised with a temporary, so you lose flexibility
X f(); void g(const X&); g(f()); // fine
X f(); void g(const X*); g(&f()); // compile error
"m sergei" <se********@yahoo.com> wrote in message
news:86**************************@posting.google.c om... void g(const X&) why is const required ? is that a requirement to inform
the compiler ?
also your second function void g(const X*). is void g(const *X) same as above ? (or correct ?)
Only const references can be bound to temporaries
X f();
void g(const X&);
void h(X&);
g(f()); // legal
h(f()); // illegal
Not all compilers enforce this rule however.
The pointer case is illegal with or without const however.
john
m sergei wrote: void g(const X&) why is const required ? is that a requirement to inform the compiler ?
It tells the compiler (as well as the programmer) that your function
doesn't modify the object it gets passed. Without it, you can't pass
constant objects to the function, and you can't pass temporary objects.
also your second function void g(const X*). is void g(const *X) same as above ? (or correct ?)
No, it's not correct. * has to follow the name of a type to show that
you want a pointer to that type. 'const' is not a type.
int& k = ... ;
(&k)[5] = 34;
-JKop
JKop wrote: int& k = ... ;
(&k)[5] = 34;
You don't actually use the reference for indexing, but rather take the
pointer to the int it refers to (&k) and use that. Sure, you could also
do:
int& k = *new int[100];
(&k)[5] = 34;
delete &k;
but it's not very useful or intuitive.
On Thu, 01 Jul 2004 13:39:55 GMT, JKop <NU**@NULL.NULL> wrote: int& k = ... ;
(&k)[5] = 34;
-JKop
What is that supposed to illustrate?
--
Bob Hairgrove No**********@Home.com
Bob Hairgrove posted: On Thu, 01 Jul 2004 13:39:55 GMT, JKop <NU**@NULL.NULL> wrote:
int& k = ... ;
(&k)[5] = 34;
-JKop
What is that supposed to illustrate?
-- Bob Hairgrove No**********@Home.com
Well it's more entertaining than the "variable" conversation that's going
on.
-JKop
JKop wrote: Well it's more entertaining than the "variable" conversation that's going on.
So you're here for entertainment? If you want that, you should try any
newsgroup that contains "advocacy" in its name.
On Thu, 01 Jul 2004 16:31:40 GMT, JKop <NU**@NULL.NULL> wrote: Bob Hairgrove posted:
On Thu, 01 Jul 2004 13:39:55 GMT, JKop <NU**@NULL.NULL> wrote:
int& k = ... ;
(&k)[5] = 34;
-JKop
What is that supposed to illustrate?
-- Bob Hairgrove No**********@Home.com
Well it's more entertaining than the "variable" conversation that's going on.
-JKop
If this isn't trolling, tell me, what is??
*plonk*
--
Bob Hairgrove No**********@Home.com
m. sergei : Question is about the difference between these two
reference to an object versus pointer to an object
What are advantages in either one and when would one use them. I see lots of examples when an object is passed as a parameter to a function it is passed as a reference. Though it would have been fine to pass it as a pointer as well ? is that right ?
I found two pages on this topic: http://www.seasite.niu.edu/cs240/CPP_Notes/Notes9.htm http://www.phptr.com/articles/articl...31783&seqNum=3
According to the latter, the use of references is handier because the
program is easier to read and write, but this is only a cosmetic
difference.
--
`cat ~/.signature`
Bob Hairgrove posted: If this isn't trolling, tell me, what is??
*plonk*
-- Bob Hairgrove No**********@Home.com
This.
-JKop
"m sergei" <se********@yahoo.com> wrote in message
news:86**************************@posting.google.c om... Question is about the difference between these two
reference to an object versus pointer to an object
What are advantages in either one and when would one use them. I see lots of examples when an object is passed as a parameter to a function it is passed as a reference. Though it would have been fine to pass it as a pointer as well ? is that right ?
Basically, a pointer is more complicated than you need. Use a reference
when you can, and a pointer only when a reference won't work.
say class is Test
then
Test *t=new Test();
t->a=9; //to access a member of class Test
how would the & reference work here (instead of *t that was used above)
like Test &t = new Test() //gives compile error
please give the correct usage with & (reference of object)
m sergei wrote: say class is Test then Test *t=new Test(); t->a=9; //to access a member of class Test
how would the & reference work here (instead of *t that was used above)
like Test &t = new Test() //gives compile error
please give the correct usage with & (reference of object)
Test & t = * new Test ();
t.a = 9;
delete & t;
--
Regards,
Buster.
Rolf Magnus wrote: [...] Sure, you could also do:
int& k = *new int[100]; (&k)[5] = 34; delete &k;
delete [] & k;
but it's not very useful or intuitive.
Agreed.
--
Regards,
Buster. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics
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