int* ptr=10;.......issue.

[al pacino]

hi ,

whats the issue with the following declaration, is it correct and what
exactly is happening here.

int main()
{
//.....
int* ptr=10; // i suppose ptr is pointing to the memory location which
stores the value 10.
//
.......
}


on gcc it gives no error...but when i compile it using g++ it gives
"invalid conversion of int * to int"

please advise on this.
regards.

[Lars Uffmann]

Re: int* ptr=10;.......i ssue.

"al pacino" <siddharthdave8 4@gmail.comwrot e:

whats the issue with the following declaration, is it correct and what
exactly is happening here.
[...]
int* ptr=10; // i suppose ptr is pointing to the memory location which
stores the value 10.

Nope, this would make the pointer point to the memory ADDRESS 10
(0xa).

on gcc it gives no error...but when i compile it using g++ it gives
"invalid conversion of int * to int"

You need to add a typecast:
int* ptr = (int *) 10;
or
int *ptr = new int[1];
*ptr = 10;
delete [] ptr;

Best Regards,

Lars

[al pacino]

Re: int* ptr=10;.......i ssue.


Lars Uffmann wrote:

"al pacino" <siddharthdave8 4@gmail.comwrot e:

whats the issue with the following declaration, is it correct and what
exactly is happening here.
[...]
int* ptr=10; // i suppose ptr is pointing to the memory location which
stores the value 10.

>
Nope, this would make the pointer point to the memory ADDRESS 10
(0xa).
>

maybe i was confused as,
char *s="hello";
implies 's' pointing to the string HELLO.

but in the original case..what was happning was
int *ptr; and
ptr=10; //ptr now points to address 10;

why is it so in the case of int as in char.

thanks and regards.

on gcc it gives no error...but when i compile it using g++ it gives
"invalid conversion of int * to int"

>
You need to add a typecast:
int* ptr = (int *) 10;
or
int *ptr = new int[1];
*ptr = 10;
delete [] ptr;
>
Best Regards,
>
Lars

or

[Salt_Peter]

Re: int* ptr=10;.......i ssue.


al pacino wrote:

hi ,
>
whats the issue with the following declaration, is it correct and what
exactly is happening here.
>
int main()
{
//.....
int* ptr=10; // i suppose ptr is pointing to the memory location which
stores the value 10.

no, thats wrong and a big no-no.
You don't understand pointers.

//
......
}
>
>
on gcc it gives no error...but when i compile it using g++ it gives
"invalid conversion of int * to int"
>
please advise on this.
regards.

That is expected. You are inducing undefined behaviour.
You are not trying to *set* what is *at* the pointer to the value of
10.
You are trying to set the memory address *in* ptr to 10.
A very big no-no (thankfully caught by most C++ compilers).

This too is illegal:

int *ptr; // ptr holds some residual value, its unitialized (bad,
no-no, danger)
*ptr = 10;

How do you know what is at that residual location?
Imagine what happens when the compiler lets you overwrite any memory
location.
Answer: UB (format the hard drive, crash the computer, etc)
You think thats a common joke - but its not a joke

Pointers are always set using the address_of (&) operator or new.

int n; // reserve integer n on the stack, although n is uninitialized
int *ptr = &n; // reserve pointer ptr on stack & its now valid: it
holds n's address
*ptr = 10; // same as n = 10

Again, ptr holds an address, *ptr is the variable at that address.
And the term in question is "dereferenc ing the pointer".
One way or another, its the program that sets the pointer.
Pointers are not a toy, when you see a pointer, except for
polymorphism, a buzzer should go off in your head. Pointers are nearly
always bad news.

pointers are hell
pointers create bugs
pointers generate headaches
a pointer is a disease
etc

Stay away from pointers, use a reference instead.
hmm, how the hell are we going to explain references to you?

[Gernot Frisch]

Re: int* ptr=10;.......i ssue.

pointers are hell
pointers create bugs
pointers generate headaches
a pointer is a disease
etc
>
Stay away from pointers, use a reference instead.

Do you come from Java? Don't make pointers that bad, because they do
have their right of existance.

hmm, how the hell are we going to explain references to you?

It's apointer - but not really a pointer.

[Robert J. Hansen]

Re: int* ptr=10;.......i ssue.

Do you come from Java? Don't make pointers that bad, because they do

have their right of existance.

Yes, when wrapped in a tr1::shared_ptr <>, or some other suitable
exceptionsafe, leak-free method of handling them.

[Rolf Magnus]

Re: int* ptr=10;.......i ssue.

al pacino wrote:

>
Lars Uffmann wrote:

>"al pacino" <siddharthdave8 4@gmail.comwrot e:

whats the issue with the following declaration, is it correct and what
exactly is happening here.
[...]
int* ptr=10; // i suppose ptr is pointing to the memory location which
stores the value 10.

>>
>Nope, this would make the pointer point to the memory ADDRESS 10
>(0xa).
>>

maybe i was confused as,
char *s="hello";
implies 's' pointing to the string HELLO.

Well, there is a difference here. That string literal is of array type. An
array gets in most cases converted to a pointer to its first element.

but in the original case..what was happning was
int *ptr; and
ptr=10; //ptr now points to address 10;
>
why is it so in the case of int as in char.

It's not char, it's char[6].

[Rolf Magnus]

Re: int* ptr=10;.......i ssue.

Gernot Frisch wrote:

>

>pointers are hell
>pointers create bugs
>pointers generate headaches
>a pointer is a disease
>etc
>>
>Stay away from pointers, use a reference instead.

>
Do you come from Java? Don't make pointers that bad, because they do
have their right of existance.

I'd say that Java references are closer to C++ pointers than to C++
references.

[peter koch]

Re: int* ptr=10;.......i ssue.


Gernot Frisch wrote:
Saltiers(?) wrote:

pointers are hell
pointers create bugs
pointers generate headaches
a pointer is a disease
etc

Stay away from pointers, use a reference instead.

>
Do you come from Java? Don't make pointers that bad, because they do
have their right of existance.
>

Is it not rather the other way around - that Java people abuse pointers
because that is the only thing they have? We "real" C++ people normally
do know that Saltiers advice (avoid pointers whenever possible) is
sound and correct.

>
>

hmm, how the hell are we going to explain references to you?

>
It's apointer - but not really a pointer.

2% truth 98% false!

/Peter

[Marcus Kwok]

Re: int* ptr=10;.......i ssue.

Salt_Peter <pj_hern@yahoo. comwrote:

Pointers are always set using the address_of (&) operator or new.

Or the null pointer value (integral constant 0).

--
Marcus Kwok
Replace 'invalid' with 'net' to reply

[Salt_Peter]

Re: int* ptr=10;.......i ssue.


Gernot Frisch wrote:

pointers are hell
pointers create bugs
pointers generate headaches
a pointer is a disease
etc

Stay away from pointers, use a reference instead.

>
Do you come from Java? Don't make pointers that bad, because they do
have their right of existance.
>

I do enjoy Java. Did you know that a Java reference is the equivalent
of a C++ pointer? Java would love to have the equivalent of a C++
reference.

>

hmm, how the hell are we going to explain references to you?

>
It's apointer - but not really a pointer.

No, a reference is an object (even when it is implemented as a pointer
down under -which is often not the case). A plain pointer is nothing
more than an adrress to something or nothing that may or may not be
valid.

[Salt_Peter]

Re: int* ptr=10;.......i ssue.


Marcus Kwok wrote:

Salt_Peter <pj_hern@yahoo. comwrote:

Pointers are always set using the address_of (&) operator or new.

>
Or the null pointer value (integral constant 0).

Indeed.

>
--
Marcus Kwok
Replace 'invalid' with 'net' to reply

[Lars Uffmann]

Re: int* ptr=10;.......i ssue.

"Salt_Peter " <pj_hern@yahoo. comwrote:

pointers are hell
pointers create bugs
pointers generate headaches
a pointer is a disease
etc
Stay away from pointers, use a reference instead.

Lol - now come on - pointers are pretty useful and impossible
to work without in many cases.

Best Regards,

Lars

[Rolf Magnus]

Re: int* ptr=10;.......i ssue.

Salt_Peter wrote:

>
Gernot Frisch wrote:

pointers are hell
pointers create bugs
pointers generate headaches
a pointer is a disease
etc
>
Stay away from pointers, use a reference instead.

>>
>Do you come from Java? Don't make pointers that bad, because they do
>have their right of existance.
>>

>
I do enjoy Java. Did you know that a Java reference is the equivalent
of a C++ pointer? Java would love to have the equivalent of a C++
reference.
>

>>

hmm, how the hell are we going to explain references to you?

>>
>It's apointer - but not really a pointer.

>
No, a reference is an object

No. That's exactly what a reference is not.

(even when it is implemented as a pointer down under -which is often not
the case).

Really? Could you elaborate? Which compilers implement them differently? I'm
seriously interested in that.

[Bo Persson]

Re: int* ptr=10;.......i ssue.


"al pacino" <siddharthdave8 4@gmail.comskre v i meddelandet
news:1156745966 .364732.210010@ i42g2000cwa.goo glegroups.com.. .

>
Lars Uffmann wrote:

>"al pacino" <siddharthdave8 4@gmail.comwrot e:

whats the issue with the following declaration, is it correct and
what
exactly is happening here.
[...]
int* ptr=10; // i suppose ptr is pointing to the memory location
which
stores the value 10.

>>
>Nope, this would make the pointer point to the memory ADDRESS 10
>(0xa).
>>

maybe i was confused as,
char *s="hello";
implies 's' pointing to the string HELLO.
>
but in the original case..what was happning was
int *ptr; and
ptr=10; //ptr now points to address 10;
>
why is it so in the case of int as in char.
>
thanks and regards.

Sorry, but you try to draw the conclusions the wrong way.

Here int follows the general rules, and char* is very special. It has
a whole set of extra rules, to be able to cope with the strange string
literal "hello" (which isn't a char!).


Bo Persson