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FAQ: How to use a pointer
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Slugsnack
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PostPosted: Sat Sep 05, 2009 11:31 am    Post subject: Reply with quote

pointers on all 32 bit systems are 4 byte
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Dark Byte
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PostPosted: Sat Sep 05, 2009 12:31 pm    Post subject: Reply with quote

to explain further since people still think there's a difference:
A pointer to a 1 byte value is 4 bytes
A pointer to a 2 byte value is 4 bytes
A pointer to a 4 byte value is 4 bytes
A pointer to a 8 byte value is 4 bytes
a pointer to a float is 4 bytes
a pointer to a double is 4 bytes
a pointer to a string is 4 bytes

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Slugsnack
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PostPosted: Sat Sep 05, 2009 4:34 pm    Post subject: Reply with quote

a pointer is saying the address of an object. so we say the address POINTS TO something. so say we had an object of 1 byte, then to locate WHERE it is in memory, there is an address for that object. the address IS THE POINTER

a pointer is simply a 4 byte value containing the address of an object. a pointer to a pointer would be a 4 byte value that holds the address of the pointer to the object

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tomcat
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PostPosted: Sun Nov 15, 2009 1:41 pm    Post subject: Reply with quote

Hi i tried this but now i have one problem. How can i prevent a crash when I try to read an adress that does not exists?
I have 3th level Pointer and the last adress does only exist sometimes ^^
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Jani
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PostPosted: Sun Nov 15, 2009 2:54 pm    Post subject: Reply with quote

tomcat wrote:
Hi i tried this but now i have one problem. How can i prevent a crash when I try to read an adress that does not exists?
I have 3th level Pointer and the last adress does only exist sometimes ^^
Windows specific: IsBadReadPtr, IsBadWritePtr.
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Slugsnack
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PostPosted: Sun Nov 15, 2009 3:12 pm    Post subject: Reply with quote

alternatively __try/__except()
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Flyte
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PostPosted: Sun Nov 15, 2009 3:17 pm    Post subject: Reply with quote

Jani wrote:
Windows specific: IsBadReadPtr, IsBadWritePtr.


They actually aren't all that good for crash protection: http://blogs.msdn.com/oldnewthing/archive/2006/09/27/773741.aspx
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Slugsnack
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PostPosted: Sun Nov 15, 2009 4:27 pm    Post subject: Reply with quote

Athaem wrote:
Jani wrote:
Windows specific: IsBadReadPtr, IsBadWritePtr.


They actually aren't all that good for crash protection: http://blogs.msdn.com/oldnewthing/archive/2006/09/27/773741.aspx

In the case that tomcat is interested in, those functions are acceptable.

You may wish to read this : http://www.cc.gatech.edu/fce/ctk/pubs/PeTe5-1.pdf

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tomcat
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PostPosted: Sun Nov 15, 2009 6:42 pm    Post subject: Reply with quote

can someone show me how to use one of this solutions?
I'm pretty new in c++ and dont get it Sad
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elshabory
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PostPosted: Sat Mar 12, 2011 11:16 am    Post subject: Reply with quote

can you kindly rewrite this code in delphi
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dpdsbd
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PostPosted: Wed Feb 12, 2014 2:12 pm    Post subject: Reply with quote

Thank you for the FAQ - however I'm not sure I understood it correctly. I have following values in CE:

(see attachment)

So if I unerstood correctly:

First step (mdnsNSP.dll+0001ED30) gives me 01132380
Second step - 01132380 + 540 should give me 00D4E1A4
When i add them as HEX - [0113280] + 540 = 11328C0, not the value above - what am I doing wrong?



snipp.PNG
 Description:
 Filesize:  12.8 KB
 Viewed:  24273 Time(s)

snipp.PNG


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Dark Byte
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PostPosted: Wed Feb 12, 2014 2:40 pm    Post subject: Reply with quote

it's [01132380 + 540] not [01132380] + 540
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dpdsbd
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PostPosted: Wed Feb 12, 2014 2:51 pm    Post subject: Reply with quote

Ok but what is the real difference - sorry but I'm spend whole day trying to figure it out and going through tons of stuff & tutorials - it being in the brackets means I should add it in a special way?
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Dark Byte
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PostPosted: Wed Feb 12, 2014 3:02 pm    Post subject: Reply with quote

Read the 4 byte value stored at 01132380 + 540 (So read the 4 bytes at 11328C0 and use that result for the next step)
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dpdsbd
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PostPosted: Wed Feb 12, 2014 3:13 pm    Post subject: Reply with quote

Right, I got it now - the problem was that I was using returned value as Hex not as Decimal.

Thank you very much! Karma+1 for you Smile
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