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Home Forums How can you compare two files byte by byte to check if they are identical? – MindStick
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1 Answers

Utpal Vishwas
Utpal Vishwas 28 May 2025
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To compare two files byte by byte in C#, you can use FileStream or File.ReadAllBytes for a full comparison. A more memory-efficient way is to stream the files and compare them block by block.

Example: Efficient Byte-by-Byte Comparison Using Streams

public static bool AreFilesIdentical(string filePath1, string filePath2)
{
    const int bufferSize = 1024 * 1024; // 1 MB buffer

    var fileInfo1 = new FileInfo(filePath1);
    var fileInfo2 = new FileInfo(filePath2);

    if (fileInfo1.Length != fileInfo2.Length)
        return false;

    using (var fs1 = new FileStream(filePath1, FileMode.Open, FileAccess.Read))
    using (var fs2 = new FileStream(filePath2, FileMode.Open, FileAccess.Read))
    {
        var buffer1 = new byte[bufferSize];
        var buffer2 = new byte[bufferSize];

        int bytesRead1, bytesRead2;
        do
        {
            bytesRead1 = fs1.Read(buffer1, 0, bufferSize);
            bytesRead2 = fs2.Read(buffer2, 0, bufferSize);

            if (bytesRead1 != bytesRead2)
                return false;

            for (int i = 0; i < bytesRead1; i++)
            {
                if (buffer1[i] != buffer2[i])
                    return false;
            }

        } while (bytesRead1 > 0);
    }

    return true;
}

Notes

  1. This approach avoids loading entire files into memory, making it suitable for large files.
  2. Comparing length first is a quick way to eliminate obviously unequal files.
  3. A File.ReadAllBytes approach is simpler but less efficient for large files.
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