VB - APP - Extracting Certain Block From Hex File

[sillybob123]

Hello,

Im new to the site and was hoping some of you could help me,

I would like to be able to open a file locate a certain offset in that file and extract up to a certain part

the item type i would want to extract is PNG from offsets

171A


to


(This number is varied depending on what size the PNG is :S*)

so put simply

Open File > Read data > Extract (171A - (See Above*) > Save it as a PNG

Oh and if needed the image will always be 64x64

Thank you very much for any help!

[Plater]

The FileStream object should accomplish what you need.

If "171A" is the value you are looking for, you can cycle through it until you find 171A and then start keeping track of what you read

if "171A" is the offset address then you can probably use the Seek() function to seek to 0x171A and then start reading/keeping track of what you read

[sillybob123]

Hey thanks for replying but im sorta new to these kinds of funtions maybe and exmaple? please,


Thanks

[Plater]

Plenty of examples as MSDN

[sillybob123]

:( This is where im at

Dim asci As System.Text.Encoding

TOP:

        Dim buffera(3) As Byte
        asci = System.Text.Encoding.ASCII
        Dim FSA As System.IO.FileStream
        FSA = System.IO.File.OpenRead(OFD.FileName)
        FSA.Seek(CONType, 0)
        FSA.Read(buffera, 0, 3)
        cnType = asci.GetString(buffera)
 
        AuthOffset = &H171A
 
 
        Dim author As String
        Dim buffer2(2678) As Byte
        asci = System.Text.Encoding.ASCII
        Dim filestream2 As System.IO.FileStream
        filestream2 = System.IO.File.OpenRead(OFD.FileName)
        filestream2.Seek(AuthOffset, 0)
        filestream2.Read(buffer2, 0, 2678)
        author = asci.GetString(buffer2)
        filestream2.Write()
        filestream2.Close()
 

Anywhere close?

[Plater]

Is 171A the value you are looking for in the file, or an offset length?

[sillybob123]

Is 171A the value you are looking for in the file, or an offset length?

171A is the start of the "block" i want and the end of the block varies like i said im not sure how to specify what to look for to complete the block,

e.g.

1 file
(Offsets)
Start = 171A

End = 2190

2nd file
(Offsets)
Start = 171A

End = 20E1

[Plater]

Well then, once you open the file you would want to call:
myFileStream.Seek(0x171A, SeekOrigin.Begin);

That will put you at the correct offset to begin reading from. Now you can start reading the data and saving it somewhere
Know you said you don't know how much to read? Well I don't know what to tell you on that.

What type of file is it that you are opening? Maybe there is headered data somewhere?

[sillybob123]

Hey thanks for the reply so do i need any of that extra stuff do i simply add what you said to the OFD_FileOk ? well the reason i dont know where it ends is because it is an image and the image will sometimes vary in size as you will know

The file = CON File

[Plater]

Are you just wanting to read to the end of the file then?
If you don't know how much you need to read, i'm not sure how you are going to do this.
I've never heard of a CON file?

CON, Configuration file, Simdir
CON, MSTS Consist file, MSTS

[sillybob123]

Hmm its ok then i will have to postpone i guess thanks for the help!

Regards,

Silly

[sillybob123]

Hmm its ok then i will have to postpone i guess thanks for the help!

Regards,

Silly

On seconds thoughts if you could maybe show me how if the end offset was


2190

Thanks

[Plater]

Ok, I'll show a quick example of how things COULD be done.
Given:
Start = 0x171A
End = 0x2190

int Start = 0x171A;
int End = 0x2190;
int lengthtoRead= End - Start;
FileStream fs =new FileStream("SomeFile.Com");//you made need to use an overload to support seek
fs.Seek(0x171A, SeekOrigin.Begin);
byte[] buff = new byte[lengthtoRead];
int ActualAmountRead = fs.Read(buff,0,buff.Length);
//now if ActualAmountRead is = lengthtoRead, then you have all your bytes in a nice byte[]
 

[sillybob123]

Thank you very much you have been so much help and i greatly appreciate it!