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Home Forums How do you read binary data from a file in C#? – MindStick
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1 Answers

Anubhav Sharma
Anubhav Sharma 19 May 2025
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To read binary data from a file in C#, you typically use one of the following:

1. File.ReadAllBytes()

Reads the entire file into a byte array.

byte[] data = File.ReadAllBytes(@"C:\path\to\file.bin");
  1. Simple and useful when the entire file can fit in memory.
  2. Returns a byte[].

2. FileStream (for reading in chunks or large files)

Gives more control for reading part of the file or working with large files.

using (FileStream fs = new FileStream(@"C:\path\to\file.bin", FileMode.Open, FileAccess.Read))
{
    byte[] buffer = new byte[fs.Length];
    int bytesRead = fs.Read(buffer, 0, buffer.Length);
}

You can also read in smaller chunks if fs.Length is too large.

3. BinaryReader (for structured binary data)

Useful if you're reading primitives like integers, floats, strings, etc., from a binary format.

using (FileStream fs = new FileStream(@"C:\path\to\file.bin", FileMode.Open, FileAccess.Read))
using (BinaryReader reader = new BinaryReader(fs))
{
    int value = reader.ReadInt32();     // Reads a 4-byte int
    double d = reader.ReadDouble();     // Reads an 8-byte double
    byte[] bytes = reader.ReadBytes(10); // Reads 10 bytes
}

Summary

Method Use Case
File.ReadAllBytes Simple, small to medium files
FileStream Large files, fine-grained control
BinaryReader Structured binary formats (e.g., headers, fixed fields)
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