Read binary file in C# from specific position

Question

Is it possible to read a large binary file from a particular position?

I don't want to read the file from the beginning because I can calculate the start position and the length of the stream I need.

All you have to do is change the Position property, or use the Seek method. Are you worried that the entire file is loaded into memory? — Marlon
– Marlon, Commented Jul 13, 2011 at 6:27
Yes, I dont want to load the entire file into memory. I use the BinaryReader and couldnt find the Seek method. --> BinaryReader.BaseStream.Seek(), thats the solution. ;-) — Skuami
– Skuami, Commented Jul 13, 2011 at 14:43
You won't have to worry about a huge file being loaded into memory. A stream only loads a portion of it at a time. Otherwise we would never be able to open huge files. — Marlon
– Marlon, Commented Jul 13, 2011 at 18:31

dodekja · Accepted Answer · 2022-11-21 21:53:47Z

15

using (FileStream sr = File.OpenRead("someFile.dat"))
{
    sr.Seek(100, SeekOrigin.Begin);
    int read = sr.ReadByte();
    //...
}

edited Nov 21, 2022 at 21:53

dodekja

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answered Jul 13, 2011 at 6:15

Petar Ivanov

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Comments

Yehuda G. · Accepted Answer · 2018-05-21 16:32:08Z

10

According to @shenhengbin answord.

Use BinaryReader.BaseStream.Seek.

using (BinaryReader b = new BinaryReader(File.Open("perls.bin", FileMode.Open)))                                                     
{
    int pos = 50000;
    int required = 2000;

    // Seek to our required position.
    b.BaseStream.Seek(pos, SeekOrigin.Begin);

    // Read the next 2000 bytes.
    byte[] by = b.ReadBytes(required);
}

answered May 21, 2018 at 16:32

Yehuda G.

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Comments

Boas Enkler · Accepted Answer · 2011-07-13 06:13:01Z

1

Well if you know streams, why not using (File)Stream.Seek(...) ?

answered Jul 13, 2011 at 6:13

Boas Enkler

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1 Comment

Skuami Over a year ago

I use the BinaryStream but I couldnt find the Seek() method. The link from Scott explains how to get the seek method on a binary reader. BinaryReader.BaseStream.Seek(pos, SeekOrigin.Begin);

Rasel · Accepted Answer · 2011-07-13 06:13:34Z

0

Of course it is possible.See this here.See the offset.you can read from the offset

answered Jul 13, 2011 at 6:13

Rasel

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1 Comment

Skuami Over a year ago

Not really, the offset defines the offset for the buffer not for the starting point of the file. I tried this way before I wrote this entry.

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