i want to access to a specific memory unit

[Vincent SHAO]

Well, i have a question here. i want to write 50000 into a specific
memory unit (like # 4321). So i wrote these:

int number=5000;
memcpy((char *)50000,(char *)&number,sizeo f(char));
char * p=(char *)50000;
cout<<"This is p"<<endl;
cout<<p<<endl;

But it doesn't work, how can i access to a specific memory unit.
Thank you.

[Ian Collins]

Re: i want to access to a specific memory unit

Vincent SHAO wrote:

Well, i have a question here. i want to write 50000 into a specific
memory unit (like # 4321). So i wrote these:
>
int number=5000;
memcpy((char *)50000,(char *)&number,sizeo f(char));
char * p=(char *)50000;
cout<<"This is p"<<endl;
cout<<p<<endl;
>
But it doesn't work, how can i access to a specific memory unit.

The answer lies in the implementation specific realm, you had better ask
on a group dedicated to your tools and or platform.

--
Ian Collins.

[Juha Nieminen]

Re: i want to access to a specific memory unit

Vincent SHAO wrote:

Well, i have a question here. i want to write 50000 into a specific
memory unit (like # 4321). So i wrote these:
>
int number=5000;
memcpy((char *)50000,(char *)&number,sizeo f(char));
char * p=(char *)50000;
cout<<"This is p"<<endl;
cout<<p<<endl;
>
But it doesn't work, how can i access to a specific memory unit.
Thank you.

"It doesn't work" tells nothing to us. What are the *symptoms* you are
seeing? Is it crashing? Is it returning the wrong value? What?

Besides, the above code is horribly non-portable, and thus not really
on-topic in this group.

[keith@bytebrothers.co.uk]

Re: i want to access to a specific memory unit

On 4 Mar, 08:41, Vincent SHAO <vincent.shao.b ...@gmail.comwr ote:

Well, i have a question here. i want to write 50000 into a specific
memory unit (like # 4321). So i wrote these:
>
memcpy((char *)50000,(char *)&number,sizeo f(char));

First, you should ask someone about the difference between 'source'
and 'destination'.

Then, ask them to explain why it is unlikely that the value 50000
would fit into something that was 'sizeof(char)' bytes long.

Then after all that, perhaps you yourself could explain why you think
that '(char*)&number ' might have anything to do with 'a specific
memory unit (like # 4321)'.

HTH.

[James Kanze]

Re: i want to access to a specific memory unit

On Mar 4, 9:57 am, Ian Collins <ian-n...@hotmail.co mwrote:

Vincent SHAO wrote:

Well, i have a question here. i want to write 50000 into a specific
memory unit (like # 4321). So i wrote these:

int number=5000;
memcpy((char *)50000,(char *)&number,sizeo f(char));
char * p=(char *)50000;
cout<<"This is p"<<endl;
cout<<p<<endl;

But it doesn't work, how can i access to a specific memory unit.

The answer lies in the implementation specific realm, you had
better ask on a group dedicated to your tools and or platform.

Mostly. The C++ part of the answer is reinterpret_cas t.

As it is, his comments don't seem to correspond to his code, and
his code seems to be trying to write 5000 into a char, which
isn't going to work on a lot of systems, for obvious reasons.
If I understand what he's trying to do, however, something like:
*reinterpret_ca st< int* >( 50000 ) = 5000 ;
should do the trick, although what that will actually do is, of
course, very, very implementation dependent. (It will generate
a core dump on the implementations I use, unless the executable
is very, very small.)

--
James Kanze (GABI Software) email:james.kan ze@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34

[Vincent SHAO]

Re: i want to access to a specific memory unit

On Mar 4, 5:07 pm, Juha Nieminen <nos...@thanks. invalidwrote:

Vincent SHAO wrote:

Well, i have a question here. i want to write 50000 into a specific
memory unit (like # 4321). So i wrote these:

>

int number=5000;
memcpy((char *)50000,(char *)&number,sizeo f(char));
char * p=(char *)50000;
cout<<"This is p"<<endl;
cout<<p<<endl;

>

But it doesn't work, how can i access to a specific memory unit.
Thank you.

>
"It doesn't work" tells nothing to us. What are the *symptoms* you are
seeing? Is it crashing? Is it returning the wrong value? What?
>
Besides, the above code is horribly non-portable, and thus not really
on-topic in this group.

Thanks for comments. The original problem is "put a byte(like 34) into
a specific memory unit (like #4321)". Here is my code
//define a byte
char number=34;
//copy the number to the memory unit #4321
memcpy((char *)4321,(char *)&number,sizeo f(char));
char * p=(char *)4321;
cout<<(int)*p<< endl;

i run the program and there is nothing out put.

And why the former code is non-portable, how judge?
Thank you

[Jeff Schwab]

Re: i want to access to a specific memory unit

Vincent SHAO wrote:

Well, i have a question here. i want to write 50000 into a specific
memory unit (like # 4321). So i wrote these:
>
int number=5000;
memcpy((char *)50000,(char *)&number,sizeo f(char));
char * p=(char *)50000;
cout<<"This is p"<<endl;
cout<<p<<endl;

You're outputting the pointer value, not the memory content.
Dereference the pointer (cout << *p).

But it doesn't work, how can i access to a specific memory unit.

[Victor Bazarov]

Re: i want to access to a specific memory unit

Jeff Schwab wrote:

Vincent SHAO wrote:

> Well, i have a question here. i want to write 50000 into a specific
>memory unit (like # 4321). So i wrote these:
>>
>int number=5000;
>memcpy((char *)50000,(char *)&number,sizeo f(char));
>char * p=(char *)50000;
>cout<<"This is p"<<endl;
>cout<<p<<end l;

>
You're outputting the pointer value, not the memory content.
Dereference the pointer (cout << *p).

I also failed to see '4321' in the code in any way. The usual
(implementation-defined) method is to use the integral value and
reinterpret_cas t it to the pointer. Perhaps this is what the
intention of declaring 'p' was...

char *p = reinterpret_cas t<char*>(4321) ;

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

[Ian Collins]

Re: i want to access to a specific memory unit

Vincent SHAO wrote:

On Mar 4, 5:07 pm, Juha Nieminen <nos...@thanks. invalidwrote:

>Vincent SHAO wrote:

>> Well, i have a question here. i want to write 50000 into a specific
>>memory unit (like # 4321). So i wrote these:
>> int number=5000;
>> memcpy((char *)50000,(char *)&number,sizeo f(char));
>> char * p=(char *)50000;
>> cout<<"This is p"<<endl;
>> cout<<p<<endl;
>>But it doesn't work, how can i access to a specific memory unit.
>>Thank you.

> "It doesn't work" tells nothing to us. What are the *symptoms* you are
>seeing? Is it crashing? Is it returning the wrong value? What?
>>
> Besides, the above code is horribly non-portable, and thus not really
>on-topic in this group.

>
Thanks for comments. The original problem is "put a byte(like 34) into
a specific memory unit (like #4321)". Here is my code
//define a byte
char number=34;
//copy the number to the memory unit #4321
memcpy((char *)4321,(char *)&number,sizeo f(char));
char * p=(char *)4321;
cout<<(int)*p<< endl;
>

Why make things so complex? sizeof(char) is 1 by definition, so you
could simply write

char* p = reinterpret_cas t<char*>(4321) ;
*p = number;

i run the program and there is nothing out put.
>
And why the former code is non-portable, how judge?

What are you running on and how do you know 4321 is a valid, writable
address?

--
Ian Collins.