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Memory I/O Question

Posted on 1998-05-29
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Last Modified: 2010-04-06
Hi,

I've got a very BIG problem with delphi 3.0.
I've got a record:

    TheRecord = record
            nr        : integer;
            name : string;            { In real it's a bit bigger, but it's just as example }
    end;

Now I'm writing a procedure that does this:
    procedure do_stuff;
    var f  : TFileStream;
          tr : ^TheRecord;
    begin
        .
        . opens file etc...
        .

        new (tr);        // reserve memory for the TheRecord
         
        { location 1}
        tr^.nr := 5;                        // This goes correctly without Exception

        f.read(tr^, sizeof(TheRecord));

        { location 2}
        tr^.nr := 5;                        // This causes an exception ???

    end;

At location 1, tr  is the address 0AB1026
                        I am able to access it's members
After reading the data, tr STILL POINTS to 0AB1026
                    But now the instruction generates an exception ??

How is this possible ?? Is it a bug in Delphi ??
btw. I've got Delphi 3.0 (build 5.53)

Can somebody help me please,
Thank you  very much in advance,

Rick Blommers
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Question by:nibbler
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8 Comments
 
LVL 5

Expert Comment

by:JimBob091197
ID: 1349158
Hi

Try f.Read(tr, SizeOf(TheRecord)).
(I.e. leave out the ^.

JB
0
 
LVL 3

Expert Comment

by:rickpet
ID: 1349159
I think you need to limit the size of your string...note long strings are now just pointers...

TheRecord = record
            nr        : integer;
            name : string[60];
    end;

Rick Peterson

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LVL 5

Expert Comment

by:JimBob091197
ID: 1349160
Hi Rickpet

I think that a string declared in a record is automatically treated as a ShortString (length 220, if I remember correctly).

Cheers,
JB
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LVL 1

Expert Comment

by:ssite
ID: 1349161
Hi everyone.

JB : I think you're wrong. Delphi 3 - Longstring unless stated othewise

I would blame this on the borland compiler. I'd bet if you do the classic of :

type
PTheRecord = ^theRecord;

and then declare the other var as PTheRecord, it should work. Let me know
0
 

Author Comment

by:nibbler
ID: 1349162
I've limited the strings, sorry for the 'incorrectness' in the example...
I used a string[50]; or something like that.

I'm also thinking it's the borland compiler, ssite I will let you know when I tried it...
0
 

Author Comment

by:nibbler
ID: 1349163
Hello Rickpet,

I've found the answer, thanks to you. I had one string item
in the record. I limited it size and gone was the exception..

Please send me an answer so I can give you the points !!

Thanks !!!

Rick
0
 
LVL 5

Expert Comment

by:JimBob091197
ID: 1349164
ssite:  You're right.  I was using different compiler settings for a project.  If Huge Strings is on in Project Options, then uses Long Strings.

Sorry for any confusion,
JB
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Accepted Solution

by:
rickpet earned 200 total points
ID: 1349165
Your welcome...

Rick
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