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Home Interviews How do you split a large file into multiple smaller files based on size? – MindStick
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1 Answers

ICSM Computer
ICSM Computer 16 May 2025
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To split a large file into multiple smaller files based on size in C#, you can:

  1. Read the large file in chunks.
  2. Write each chunk to a new file when the size limit is reached.

Example: Split File by Size in MB

using System;
using System.IO;

class FileSplitter
{
    public static void SplitFile(string inputFile, string outputDir, int maxSizeInMB)
    {
        const int bufferSize = 1024 * 1024; // 1 MB
        byte[] buffer = new byte[bufferSize];
        int partNumber = 1;
        long maxBytesPerFile = maxSizeInMB * 1024L * 1024L;

        using FileStream sourceStream = new FileStream(inputFile, FileMode.Open, FileAccess.Read);
        Directory.CreateDirectory(outputDir);

        while (sourceStream.Position < sourceStream.Length)
        {
            string partFileName = Path.Combine(outputDir, $"{Path.GetFileNameWithoutExtension(inputFile)}.part{partNumber}{Path.GetExtension(inputFile)}");
            using FileStream partStream = new FileStream(partFileName, FileMode.Create, FileAccess.Write);

            long bytesWritten = 0;
            while (bytesWritten < maxBytesPerFile && sourceStream.Position < sourceStream.Length)
            {
                int bytesToRead = (int)Math.Min(bufferSize, maxBytesPerFile - bytesWritten);
                int bytesRead = sourceStream.Read(buffer, 0, bytesToRead);
                partStream.Write(buffer, 0, bytesRead);
                bytesWritten += bytesRead;
            }

            Console.WriteLine($"Created: {partFileName}");
            partNumber++;
        }
    }
}

Usage

FileSplitter.SplitFile("largefile.zip", "output", 10); // Split into 10 MB parts

Notes

  1. This example uses binary splitting, suitable for any file type.
  2. Files are named like largefile.part1.zip, largefile.part2.zip, etc.
  3. To merge them later, you'd read them in order and write to a single file.

Read More

  1. How do you log all file system operations (create, read, write, delete) in an application?
  2. How do you serialize and save an object to a binary file?
  3. How can you throttle file read/write speed to simulate slow I/O conditions?
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