function return pointer of int?

[Davy]

Hi all,

I am writing a function, which return the pointer of the int. But it
seems to be wrong. Any suggestion?

int * get_p_t(int t) {
return &t;
}

int main()
{
printf("v1\n");
int t = 5;
int * p_t[2];

p_t[0] = &t; // right
p_t[1] = get_p_t(t); //wrong

return 0;
}

Best regards,
Davy

[Ian Collins]

Davy wrote:

Hi all,

I am writing a function, which return the pointer of the int. But it
seems to be wrong. Any suggestion?

int * get_p_t(int t) {
return &t;
}

t is effectively a local variable in get_p_t. So the address you return
will be invalid after the function returns.

--
Ian Collins

[Davy]

On Nov 5, 2:49*pm, Ian Collins <[e-mail] mwrote:

Davy wrote:

Hi all,

I am writing a function, which return the pointer of the int. But it
seems to be wrong. Any suggestion?

int * get_p_t(int t) {
* * return &t;
}

t is effectively a local variable in get_p_t. *So the address you return
will be invalid after the function returns.

Hi Ian, thank you,

But how can I get the address of t in the main() scope, if I want to
use function?

>
--
Ian Collins

[Ian Collins]

Davy wrote:

On Nov 5, 2:49 pm, Ian Collins <[e-mail] mwrote:

>Davy wrote:

>>Hi all,
I am writing a function, which return the pointer of the int. But it
seems to be wrong. Any suggestion?
int * get_p_t(int t) {
return &t;
}

t is effectively a local variable in get_p_t. So the address you return
will be invalid after the function returns.

Hi Ian, thank you,

But how can I get the address of t in the main() scope, if I want to
use function?

You can't. You get the address of where t was.

--
Ian Collins

[DJ Dharme]

On Nov 5, 12:12*pm, Ian Collins <[e-mail] mwrote:

Davy wrote:

On Nov 5, 2:49 pm, Ian Collins <[e-mail] mwrote:

Davy wrote:
Hi all,
I am writing a function, which return the pointer of the int. But it
seems to be wrong. Any suggestion?
int * get_p_t(int t) {
* * return &t;
}
t is effectively a local variable in get_p_t. *So the address you return
will be invalid after the function returns.

Hi Ian, thank you,

But how can I get the address of t in the main() scope, if I want to
use function?

You can't. *You get the address of where t was.

--
Ian Collins

Still he can get a reference or a pointer to t as the input parameter
and return a valid pointer.

[=?ISO-8859-1?Q?Marcel_M=FCller?=]

Hi

Davy schrieb:

>>int * get_p_t(int t) {
return &t;
}

t is effectively a local variable in get_p_t. So the address you return
will be invalid after the function returns.

But how can I get the address of t in the main() scope, if I want to
use function?

int * get_p_t(int & t) {
return &t;
}

will do the job, but it still makes little sense since you stil may
receive a local address from the caller. At least it should be well
documented the the argument to get_p_t has to be valid at least as long
as the return value is used.
[Only posted to the c++ group]
Marcel

[Ian Collins]

DJ Dharme wrote:

On Nov 5, 12:12 pm, Ian Collins <[e-mail] mwrote:

>Davy wrote:

>>On Nov 5, 2:49 pm, Ian Collins <[e-mail] mwrote:
Davy wrote:
Hi all,
I am writing a function, which return the pointer of the int. But it
seems to be wrong. Any suggestion?
int * get_p_t(int t) {
return &t;
}
t is effectively a local variable in get_p_t. So the address you return
will be invalid after the function returns.
Hi Ian, thank you,
But how can I get the address of t in the main() scope, if I want to
use function?

You can't. You get the address of where t was.

Still he can get a reference or a pointer to t as the input parameter
and return a valid pointer.

Do what?

--
Ian Collins

[Nick Keighley]

On 5 Nov, 07:06, Davy <zhushe...@gmai l.comwrote:

On Nov 5, 2:49*pm, Ian Collins <[e-mail] mwrote:

Davy wrote:

Hi all,

I am writing a function, which return the pointer of the int. But it
seems to be wrong. Any suggestion?

int * get_p_t(int t) {
* * return &t;
}

t is effectively a local variable in get_p_t. *So the address you return
will be invalid after the function returns.

Hi Ian, thank you,

But how can I get the address of t in the main() scope, if I want to
use function?

as Ian Collins said "you can't".

Why do you want to do this? I'm not being awkward if you explain
your larger problem, the context in which you want the address of t
we might be able to suggest a workaround.

int main (void)
{
printf("v1\n");
int t = 5;
int * p_t[2];

p_t[0] = &t;
p_t[1] = get_p_t(t);

/*** you have the address of t by using &t.
why do you want a function to do this? */

return 0;
}

--
Nick Keighley

[vippstar]

On Nov 5, 9:31 am, DJ Dharme <donjuandharmap [e-mail] ote:

On Nov 5, 12:12 pm, Ian Collins <[e-mail] mwrote:

Davy wrote:

On Nov 5, 2:49 pm, Ian Collins <[e-mail] mwrote:
>Davy wrote:
>>Hi all,
>>I am writing a function, which return the pointer of the int. But it
>>seems to be wrong. Any suggestion?
>>int * get_p_t(int t) {
>> return &t;
>>}
>t is effectively a local variable in get_p_t. So the address you return
>will be invalid after the function returns.

Hi Ian, thank you,

But how can I get the address of t in the main() scope, if I want to
use function?

You can't. You get the address of where t was.

--
Ian Collins

Still he can get a reference or a pointer to t as the input parameter
and return a valid pointer.

Please don't quote signatures. (the text after --)
Also, no, he can't. I think his function is valid, ie this code is
valid:

int *foo(int i) { return &i; }

However even evaluating foo(anything) invokes undefined behavior,
since the object pointed to by the pointer is over its lifetime, and
the pointer becomes indeterminate. (either unspecified value or trap
representation)

[James Kuyper]

Davy wrote:

On Nov 5, 2:49 pm, Ian Collins <[e-mail] mwrote:

>Davy wrote:

>>Hi all,
I am writing a function, which return the pointer of the int. But it
seems to be wrong. Any suggestion?
int * get_p_t(int t) {
return &t;
}

t is effectively a local variable in get_p_t. So the address you return
will be invalid after the function returns.

Hi Ian, thank you,

But how can I get the address of t in the main() scope, if I want to
use function?

int * get_p_int(int *pt) { return pt;}

int main(void)
{
int t;
int *p = get_p_int(&t);
Of course, this is pretty pointless; get_p_int(&t) doesn't get you
anything that &t doesn't already get you. So you might as well writer

int *p = &t;

So, what is the real problem you're trying to solve?