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Home Interviews How do you write structured data (like CSV) to a file in C#? – MindStick
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1 Answers

ICSM Computer
ICSM Computer 07 May 2025
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In C#, you can write structured data like CSV using simple StreamWriter or File.WriteAllText/File.AppendAllText. CSV (Comma-Separated Values) format is just plain text with values separated by commas, and optionally enclosed in quotes if they contain commas or special characters.

Basic CSV Writing Example with StreamWriter

using System;
using System.IO;

class Program
{
    static void Main()
    {
        string csvPath = @"C:\output.csv";

        using (StreamWriter writer = new StreamWriter(csvPath))
        {
            // Write header
            writer.WriteLine("Id,Name,Email");

            // Write data rows
            writer.WriteLine("1,John Doe,john@example.com");
            writer.WriteLine("2,Jane Smith,jane@example.com");
            writer.WriteLine("3,\"O'Brien, Sam\",sam@example.com"); // Quotes needed for comma in name
        }

        Console.WriteLine("CSV written to: " + csvPath);
    }
}

Handling Special Characters

Enclose fields in double quotes if they contain commas, quotes, or newlines.

Escape quotes inside a field by doubling them:
"He said ""Hello""" → becomes He said "Hello"

Optional: Generate CSV from a List of Objects

class Person
{
    public int Id;
    public string Name;
    public string Email;
}

var people = new List<Person>
{
    new Person { Id = 1, Name = "John Doe", Email = "john@example.com" },
    new Person { Id = 2, Name = "Jane Smith", Email = "jane@example.com" }
};

using (StreamWriter writer = new StreamWriter(@"C:\people.csv"))
{
    writer.WriteLine("Id,Name,Email");
    foreach (var person in people)
    {
        string name = person.Name.Contains(",") ? $"\"{person.Name}\"" : person.Name;
        writer.WriteLine($"{person.Id},{name},{person.Email}");
    }
}

Tip: Use a CSV library like CsvHelper for large or complex data sets.

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