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Reading bytes from a specific address in a file
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Author
Topic: Reading bytes from a specific address in a file (Read 1685 times)
DumDum
New Member
Posts: 32
Reading bytes from a specific address in a file
«
on:
July 23, 2018, 12:14:49 pm »
Hi,
Wondering if there is a way to display specific bytes on the screen from a predesignated address in a binary file.
C
Logged
taazz
Hero Member
Posts: 5368
Re: Reading bytes from a specific address in a file
«
Reply #1 on:
July 23, 2018, 12:38:55 pm »
In general, yes there are a couple of ways. Here is one example using streams.
Code: Pascal
[Select]
[+]
[-]
function
ReadBytes
(
const
aFilename
:
string
;
aOffset
,
aCount
:
Int64
)
:
TByteArray
;
var
vFile
:
TFileStream
;
begin
vfile
:
=
TFileStream
.
Create
(
aFilename
,
fmOpenReadWrite
or
fmShareExclusive
)
;
try
SetLength
(
Result
,
aCount
)
;
vFile
.
Seek
(
aOffset
,
soFromBeginning
)
;
vFile
.
Read
(
Result
[
0
]
,
aCount
)
;
finally
vFile
.
Free
;
end
;
end
;
here is the same procedure using binary files.
Code: Pascal
[Select]
[+]
[-]
function
ReadBytes
(
const
aFilename
:
string
;
aOffset
,
aCount
:
Int64
)
:
TByteArray
;
var
vFile
:
File
;
begin
AssignFile
(
vFile
,
aFilename
)
;
Reset
(
vFile
,
1
)
;
try
SetLength
(
Result
,
aCount
)
;
Seek
(
vFile
,
aOffset
)
;
BlockRead
(
vFile
,
Result
[
0
]
,
aCount
)
;
finally
CloseFile
(
vFile
)
;
end
;
end
;
Logged
Good judgement is the result of experience … Experience is the result of bad judgement.
OS : Windows 7 64 bit
Laz: Lazarus 1.4.4 FPC 2.6.4 i386-win32-win32/win64
Bart
Hero Member
Posts: 5275
Re: Reading bytes from a specific address in a file
«
Reply #2 on:
July 23, 2018, 01:26:50 pm »
IIRC then blockread can only read chunks of size word (max 65536 bytes)?
At least that was the case in the old days.
Bart
Logged
taazz
Hero Member
Posts: 5368
Re: Reading bytes from a specific address in a file
«
Reply #3 on:
July 23, 2018, 01:31:55 pm »
lazarus 1.4.4 has an overloaded version of blockread with int64 see attachement.
Logged
Good judgement is the result of experience … Experience is the result of bad judgement.
OS : Windows 7 64 bit
Laz: Lazarus 1.4.4 FPC 2.6.4 i386-win32-win32/win64
Thaddy
Hero Member
Posts: 14204
Probably until I exterminate Putin.
Re: Reading bytes from a specific address in a file
«
Reply #4 on:
July 23, 2018, 01:54:54 pm »
And when you declare a File of record, you can read any - packed - record by its index.
Logged
Specialize a type, not a var.
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Reading bytes from a specific address in a file
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