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Java - read bytes at a given offset

I am having a little trouble understanding how I can read and return the value of a specific offset position in a file.

For example, from my hex editor, I know the offset is D768 and the value is 32 bits. So how can this value be read and displayed in the label.

Any help would be generally appreciated.

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4 answers


I think java.io.RandomAccessFile is your new friend :-)

Beware of the following code, it hasn't been tested.



RandomAccessFile raf = new RandomAccessFile("foo.bin", "r");
raf.seek(0xd768);
int value = raf.read();
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Use the DataInputStream class. Open the file and place it with skipBytes(offset)

and then call readInt()

. This will give you 32 bits, starting at the offset you are using.



(Note that this assumes the integer is in the most significant byte file.)

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Use skipBytes

to jump to a preset position. To read a 32 bit number, you can use DataInputStream

if value is big-endian. If it's a bit, you need to manually convert four bytes to int

:

int value = (int)bytes[0]
        | ((int)bytes[1] << 8)
        | ((int)bytes[2] << 16)
        | ((int)bytes[3] << 24);
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Refuse to skip RandomAccessFile.skipBytes before offset, this class can help you.

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