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digitalmars.D.learn - Working with pointers/adresses

reply Quantium <qchessv2 gmail.com> writes:
I'm learning now memory usage in D, and I have the problem that I 
can't solve.
The problem is (The third step):
1) Programm gets number (In int format) as input data.
2) Integer is converted to HEX
3) Programm gets the data in 0x<Integer converted to HEX> memory 
slot and writes it in the console.
Jul 08 2020
parent reply Paul Backus <snarwin gmail.com> writes:
On Wednesday, 8 July 2020 at 19:48:07 UTC, Quantium wrote:

 I'm learning now memory usage in D, and I have the problem that 
 I can't solve.
 The problem is (The third step):
 1) Programm gets number (In int format) as input data.
 2) Integer is converted to HEX
 3) Programm gets the data in 0x<Integer converted to HEX> 
 memory slot and writes it in the console.


import std.stdio;

void main()
{
     int i;
     readf("%d\n", i); // read a number
     ubyte* p = cast(ubyte*) i; // convert it to a pointer
     writeln(*p); // write the data at that address to the console
}

Note that this program will almost certainly crash if you try to 
run it, since modern computers do not allow programs to read and 
write arbitrary memory locations.
Jul 08 2020
next sibling parent reply Quantium <qchessv2 gmail.com> writes:
I have one more question. I tested the programm, as you said, it 
worked rarely because of OS restrictions. If I compile that code 
to dll, and run it through dll launcher, should it work?
Jul 09 2020
next sibling parent "H. S. Teoh" <hsteoh quickfur.ath.cx> writes:
On Thu, Jul 09, 2020 at 04:16:53PM +0000, Quantium via Digitalmars-d-learn
wrote:

 I have one more question. I tested the programm, as you said, it
 worked rarely because of OS restrictions. If I compile that code to
 dll, and run it through dll launcher, should it work?


No, it's subject to the same restrictions.  Why should it be otherwise?


T

-- 
Let's call it an accidental feature. -- Larry Wall
Jul 09 2020
prev sibling parent Paul Backus <snarwin gmail.com> writes:
On Thursday, 9 July 2020 at 16:16:53 UTC, Quantium wrote:

 I have one more question. I tested the programm, as you said, 
 it worked rarely because of OS restrictions. If I compile that 
 code to dll, and run it through dll launcher, should it work?


The OS restrictions don't care whether your program is in a dll 
or not, so you will get more or less the same results (though the 
specific addresses that do and don't work might change).
Jul 09 2020
prev sibling parent reply matheus <matheus gmail.com> writes:
On Wednesday, 8 July 2020 at 20:33:39 UTC, Paul Backus wrote:

 import std.stdio;

 void main()
 {
     int i;
     readf("%d\n", i); // read a number
     ubyte* p = cast(ubyte*) i; // convert it to a pointer
     writeln(*p); // write the data at that address to the 
 console
 }

 Note that this program will almost certainly crash if you try 
 to run it, since modern computers do not allow programs to read 
 and write arbitrary memory locations.


I wonder if the question was more like intended to display the 
value using pointers, ie:

import std.stdio;

void main(){
     int i;
     readf("%d\n", i);
     int *p = &i;
     writeln(*p);
}

Because accessing arbitrary memory location seems very weird.

Matheus.
Jul 09 2020
next sibling parent matheus <matheus gmail.com> writes:
On Thursday, 9 July 2020 at 17:24:33 UTC, matheus wrote:

 On Wednesday, 8 July 2020 at 20:33:39 UTC, Paul Backus wrote:

 import std.stdio;

 void main()
 {
     int i;
     readf("%d\n", i); // read a number
     ubyte* p = cast(ubyte*) i; // convert it to a pointer
     writeln(*p); // write the data at that address to the 
 console
 }

 Note that this program will almost certainly crash if you try 
 to run it, since modern computers do not allow programs to 
 read and write arbitrary memory locations.


 I wonder if the question was more like intended to display the 
 value using pointers, ie:

 import std.stdio;

 void main(){
     int i;
     readf("%d\n", i);
     int *p = &i;
     writeln(*p);
 }

 Because accessing arbitrary memory location seems very weird.

 Matheus.


Or maybe he wanted to do this:

import std.stdio;

void main(){
     int i;
     readf("%d\n", i);
     ulong address = cast(ulong)&i;
     ubyte* p = cast(ubyte*)address;
     writeln(*p);
}

Matheus.
Jul 09 2020
prev sibling parent "H. S. Teoh" <hsteoh quickfur.ath.cx> writes:
On Thu, Jul 09, 2020 at 05:24:33PM +0000, matheus via Digitalmars-d-learn wrote:
[...]

 I wonder if the question was more like intended to display the value
 using pointers, ie:
 
 import std.stdio;
 
 void main(){
     int i;
     readf("%d\n", i);
     int *p = &i;
     writeln(*p);
 }
 
 Because accessing arbitrary memory location seems very weird.


[...]

Unless the goal was to write an OS? ;-)


T

-- 
It only takes one twig to burn down a forest.
Jul 09 2020