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Home Interviews How do you read a large file efficiently without loading the entire content into memory? – MindStick
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1 Answers

ICSM Computer
ICSM Computer 06 May 2025
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To read a large file efficiently in C# without loading the entire content into memory, you should read it line-by-line or in chunks using streams like StreamReader or FileStream.

Option 1: Line-by-line with StreamReader (best for text files)

using System;
using System.IO;

class Program
{
    static void Main()
    {
        using (StreamReader reader = new StreamReader("largefile.txt"))
        {
            string line;
            while ((line = reader.ReadLine()) != null)
            {
                // Process each line
                Console.WriteLine(line);
            }
        }
    }
}

This method uses minimal memory, making it ideal for log files, CSVs, etc.

Option 2: Read in byte chunks using FileStream (best for binary or structured data)

using System;
using System.IO;

class Program
{
    static void Main()
    {
        byte[] buffer = new byte[4096]; // 4KB buffer

        using (FileStream fs = new FileStream("largefile.dat", FileMode.Open, FileAccess.Read))
        {
            int bytesRead;
            while ((bytesRead = fs.Read(buffer, 0, buffer.Length)) > 0)
            {
                // Process the bytes
                Console.WriteLine($"Read {bytesRead} bytes");
            }
        }
    }
}

This approach is efficient for reading raw or binary data in segments.

Key Benefits

  1. Avoids high memory usage.
  2. Scales well with very large files (GBs or more).
  3. Works well for streaming scenarios.
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