| Author |
How to increment both the pointer and the content of the pointer
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| How do you increment a pointer to an integer
(increment both the pointer and the content of the pointer)?
| |
| Mark Randall 2006-05-21, 7:11 pm |
| int* blah = somearray;
blah++;
?
--
- Mark Randall
http://www.temporal-solutions.co.uk
"We're Systems and Networks..."
"It's our job to know..."
"Ben" <boningho@gmail.com> wrote in message
news:ey0RUhTfGHA.1264@TK2MSFTNGP05.phx.gbl...
> How do you increment a pointer to an integer
> (increment both the pointer and the content of the pointer)?
>
| |
| John Carson 2006-05-21, 7:11 pm |
| "Ben" <boningho@gmail.com> wrote in message
news:ey0RUhTfGHA.1264@TK2MSFTNGP05.phx.gbl
> How do you increment a pointer to an integer
> (increment both the pointer and the content of the pointer)?
How about :
#include <iostream>
using namespace std;
int main()
{
int array[] = {0,1,2,3,4,5,6,7,9};
size_t arraySize = sizeof(array)/sizeof(array[0]);
int *ptr = array;
// display initial array
for(size_t i=0; i<arraySize; ++i)
cout << array[i] << '\n';
cout << "\n\n";
// do the incrementing
while (ptr != array+arraySize )
{
++*ptr;
++ptr;
}
// display modified array
for(size_t i=0; i<arraySize; ++i)
cout << array[i] << '\n';
return 0;
}
--
John Carson
| |
| Jonathan Wood 2006-05-21, 10:09 pm |
| int *pInt;
// Initialize pInt to point to an integer
// Increment the content of the pointer
*pInt;
// Increment the pointer (will now point to something else)
pInt++;
--
Jonathan Wood
SoftCircuits Programming
http://www.softcircuits.com
"Ben" <boningho@gmail.com> wrote in message
news:ey0RUhTfGHA.1264@TK2MSFTNGP05.phx.gbl...
> How do you increment a pointer to an integer
> (increment both the pointer and the content of the pointer)?
>
| |
|
| Dear John,
This is GREAT, thanks you a lot.
Ben
"John Carson" <jcarson_n_o_sp_am_@netspace.net.au> wrote in message
news:eCqeJvTfGHA.1276@TK2MSFTNGP03.phx.gbl...
> "Ben" <boningho@gmail.com> wrote in message
> news:ey0RUhTfGHA.1264@TK2MSFTNGP05.phx.gbl
>
> How about :
>
> #include <iostream>
> using namespace std;
>
> int main()
> {
> int array[] = {0,1,2,3,4,5,6,7,9};
> size_t arraySize = sizeof(array)/sizeof(array[0]);
> int *ptr = array;
>
> // display initial array
> for(size_t i=0; i<arraySize; ++i)
> cout << array[i] << '\n';
>
> cout << "\n\n";
>
> // do the incrementing
> while (ptr != array+arraySize )
> {
> ++*ptr;
> ++ptr;
> }
>
> // display modified array
> for(size_t i=0; i<arraySize; ++i)
> cout << array[i] << '\n';
>
>
> return 0;
> }
>
>
> --
> John Carson
>
>
>
| |
|
| another question:
can I combine these two line:
++*ptr;
++ptr;
into a single statement?
"John Carson" <jcarson_n_o_sp_am_@netspace.net.au> wrote in message
news:eCqeJvTfGHA.1276@TK2MSFTNGP03.phx.gbl...
> "Ben" <boningho@gmail.com> wrote in message
> news:ey0RUhTfGHA.1264@TK2MSFTNGP05.phx.gbl
>
> How about :
>
> #include <iostream>
> using namespace std;
>
> int main()
> {
> int array[] = {0,1,2,3,4,5,6,7,9};
> size_t arraySize = sizeof(array)/sizeof(array[0]);
> int *ptr = array;
>
> // display initial array
> for(size_t i=0; i<arraySize; ++i)
> cout << array[i] << '\n';
>
> cout << "\n\n";
>
> // do the incrementing
> while (ptr != array+arraySize )
> {
> ++*ptr;
> ++ptr;
> }
>
> // display modified array
> for(size_t i=0; i<arraySize; ++i)
> cout << array[i] << '\n';
>
>
> return 0;
> }
>
>
> --
> John Carson
>
>
>
| |
| Carl Daniel [VC++ MVP] 2006-05-21, 10:09 pm |
| "John Carson" <jcarson_n_o_sp_am_@netspace.net.au> wrote in message
news:eCqeJvTfGHA.1276@TK2MSFTNGP03.phx.gbl...
> "Ben" <boningho@gmail.com> wrote in message
> news:ey0RUhTfGHA.1264@TK2MSFTNGP05.phx.gbl
>
> // do the incrementing
> while (ptr != array+arraySize )
> {
> ++*ptr;
> ++ptr;
or, for the really  istic, replace the two lines above with:
++*ptr++;
-cd
| |
|
| Is this two statements equal?
++*ptr++;
(++(*(ptr++)));
"Carl Daniel [VC++ MVP]" <cpdaniel_remove_this_and_nospam@mvps.org.nospam>
wrote in message news:OAo5jBUfGHA.764@TK2MSFTNGP03.phx.gbl...
> "John Carson" <jcarson_n_o_sp_am_@netspace.net.au> wrote in message
> news:eCqeJvTfGHA.1276@TK2MSFTNGP03.phx.gbl...
>
>
> or, for the really istic, replace the two lines above with:
>
> ++*ptr++;
>
> -cd
>
>
| |
| Igor Tandetnik 2006-05-21, 10:09 pm |
| "Ben" <boningho@gmail.com> wrote in message
news:OlPFI$TfGHA.5088@TK2MSFTNGP02.phx.gbl
> another question:
>
> can I combine these two line:
> ++*ptr;
> ++ptr;
> into a single statement?
++(*ptr++);
but just because you can doesn't mean it's actually a good idea to use
something cute like this in your production code.
--
With best wishes,
Igor Tandetnik
With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925
| |
| Carl Daniel [VC++ MVP] 2006-05-22, 4:19 am |
| Ben wrote:
> Is this two statements equal?
>
> ++*ptr++;
> (++(*(ptr++)));
Yes. From the inside out:
1. take the value of ptr
2. increment ptr
3. dereference the value obtained in step 1
4. increment the value at that address
-cd
| |
|
| Thank you, now I make more clear on pointer behavior.
Ben
"Carl Daniel [VC++ MVP]" <cpdaniel_remove_this_and_nospam@mvps.org.nospam>
wrote in message news:O7uUe4VfGHA.4304@TK2MSFTNGP05.phx.gbl...
> Ben wrote:
>
> Yes. From the inside out:
>
> 1. take the value of ptr
> 2. increment ptr
> 3. dereference the value obtained in step 1
> 4. increment the value at that address
>
> -cd
>
>
| |
| David Webber 2006-05-22, 7:15 pm |
|
"Ben" <boningho@gmail.com> wrote in message
news:Oyp0mWWfGHA.1792@TK2MSFTNGP03.phx.gbl...
> Thank you, now I make more clear on pointer behavior.
I'd advise getting a table of C++ operator precedence rules if you're even
*thinking* of doing anything like this!
And irrespective of how confident you are, still use brackets or multiple
statements.
Even in simple case like
y = a*x+b;
I often prefer
y = (a*x) + b;
though in that case I usually don't go quite as far as
y = a*x;
y += b;
The brackets, when they are not needed, cost nothing in your code. Missing
them out where they are needed can cost hours of debugging time, or worse.
Dave
--
David Webber
Author MOZART the music processor for Windows -
http://www.mozart.co.uk
For discussion/support see
http://www.mozart.co.uk/mzusers/mailinglist.htm
| |
| Carl Daniel [VC++ MVP] 2006-05-22, 7:15 pm |
| "David Webber" <dave@musical.demon.co.uk> wrote in message
news:%23%23$nQ4bfGHA.4496@TK2MSFTNGP03.phx.gbl...
>
> "Ben" <boningho@gmail.com> wrote in message
> news:Oyp0mWWfGHA.1792@TK2MSFTNGP03.phx.gbl...
>
>
> I'd advise getting a table of C++ operator precedence rules if you're even
> *thinking* of doing anything like this!
Absolutely! While I did offer the example, if I saw code like that during a
code review, I'd be having a talk with the author!
>
> And irrespective of how confident you are, still use brackets or multiple
> statements.
>
> Even in simple case like
>
> y = a*x+b;
>
> I often prefer
>
> y = (a*x) + b;
>
> though in that case I usually don't go quite as far as
>
> y = a*x;
> y += b;
>
> The brackets, when they are not needed, cost nothing in your code.
> Missing them out where they are needed can cost hours of debugging time,
> or worse.
Agreed 100%!
-cd
| |
| Tim Roberts 2006-05-24, 4:16 am |
| "Jonathan Wood" <jwood@softcircuits.com> wrote:
>int *pInt;
>
>// Initialize pInt to point to an integer
>
>// Increment the content of the pointer
>*pInt;
Why do you think that increments the content of the pointer?
--
- Tim Roberts, timr@probo.com
Providenza & Boekelheide, Inc.
| |
| Jonathan Wood 2006-05-24, 7:10 pm |
| Because I did not realize I had a syntax error when I wrote it.
--
Jonathan Wood
SoftCircuits Programming
http://www.softcircuits.com
"Tim Roberts" <timr@probo.com> wrote in message
news:ots7721mfgt9o6fc64bieviqk5qfg8k2ns@
4ax.com...
> "Jonathan Wood" <jwood@softcircuits.com> wrote:
>
>
> Why do you think that increments the content of the pointer?
> --
> - Tim Roberts, timr@probo.com
> Providenza & Boekelheide, Inc.
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