Working with CSV Files in C#

A Comma Separated Values (CSV) file is a common and simple format for storing tabular data, where each item is separated by a comma. Each line in a CSV file represents a record, and each comma-separated item is a field within that record. CSV files are widely used for storing structured data such as contact lists, to-do lists, and simple databases because they are easy to read and write.

Understanding CSV Structure

A CSV file has a straightforward structure where:

• Each line in the file corresponds to a single record.
• Each field within a record is separated by a comma.

For example, consider the following to-do list stored in a CSV file:

13/04/2021,Apply for job,In progress
13/04/2021,Clean out hamster cage,Not Started
14/04/2021,Take car in for service,Not Started
15/04/2021,Buy birthday card for brother,Not Started

Each line represents a task with three fields: the due date, the task description, and its status.

Writing to a CSV File

Let’s create a simple program to add new tasks to our to-do list and save them in a CSV file. Here's how you can do it:

using System;
using System.IO;

namespace csvfiles
{
    class Program
    {
        static void Main(string[] args)
        {
            DateTime taskDueDate;
            string task;
            string status;

            Console.Clear();
            Console.WriteLine("TODO Manager");

            // Getting input from the user
            Console.WriteLine("Enter the task: ");
            Console.Write("Due Date (e.g., 13/04/2021): > ");
            taskDueDate = Convert.ToDateTime(Console.ReadLine());
            Console.Write("Description: > ");
            task = Console.ReadLine();
            Console.Write("Status: > ");
            status = Console.ReadLine();

            // Writing to CSV file
            string filename = "todo.csv";
            using (StreamWriter sw = new StreamWriter(filename, true))
            {
                sw.WriteLine($"{taskDueDate.ToShortDateString()},{task},{status}");
            }

            Console.WriteLine("Task added successfully!");
        }
    }
}

• Getting User Input: We prompt the user to enter the due date, description, and status of the task.
• Writing to the File: The program writes the new task to the file todo.csv using StreamWriter. The true parameter in the StreamWriter constructor enables append mode, which prevents overwriting existing data.
• String Interpolation: We use string interpolation ($"{taskDueDate.ToShortDateString()},{task},{status}") to format the data into a single line, with each field separated by a comma.

Note

The DateTime field is converted using ToShortDateString() to only store the date, not the time.

Reading from a CSV File

To read and process the data stored in a CSV file, we need to read each line and split it into its individual fields using the Split() method.

Here’s how we can read the data from the todo.csv file and display it:

using System;
using System.IO;

namespace csvfiles
{
    class Program
    {
        struct Todo
        {
            public DateTime taskDueDate;
            public string task;
            public string status;

            public override string ToString()
            {
                return $"{taskDueDate.ToShortDateString()} : {task} ({status})";
            }
        }

        static void Main(string[] args)
        {
            string filename = "todo.csv";
            try
            {
                using (StreamReader sr = new StreamReader(filename))
                {
                    Todo taskItem;
                    string line;

                    Console.WriteLine("TODO List:");

                    while ((line = sr.ReadLine()) != null)
                    {
                        string[] items = line.Split(',');
                        taskItem.taskDueDate = Convert.ToDateTime(items[0]);
                        taskItem.task = items[1];
                        taskItem.status = items[2];
                        Console.WriteLine(taskItem.ToString());
                    }
                }
            }
            catch (FileNotFoundException)
            {
                Console.WriteLine($"File {filename} not found.");
            }
            catch (IOException ex)
            {
                Console.WriteLine($"An I/O error occurred: {ex.Message}");
            }
        }
    }
}

• Reading the CSV File: The program reads each line from the todo.csv file using StreamReader.
• Splitting the Line: Each line is split into an array of fields using Split(',').
• Mapping to struct: The values from the array are assigned to the taskItem struct fields: taskDueDate, task, and status.
• Displaying the Data: The ToString() method is overridden to display the data in a readable format.

Using struct for Data Management

Using a struct helps organize the data, making it easier to manage and process. The Todo struct represents each task, holding the due date, description, and status of the task.

Best Practices for Working with CSV Files

1. Error Handling: Always use try...catch blocks to handle potential exceptions, such as missing files or I/O errors.
2. Append Mode: Use the append mode (true parameter in StreamWriter) to add new data without overwriting existing content.
3. Data Validation: Validate user input to ensure it is in the correct format (e.g., date format) before writing to the file.
4. Use struct or class: For complex data structures, use a struct or class to represent each record, making the code more readable and maintainable.

Exercise

1. Extend the Program: Modify the program to allow users to update or delete tasks in the CSV file.
2. Search Functionality: Implement a search function to find tasks by their status or due date.
3. Data Validation: Add data validation to ensure the date and status are entered correctly by the user.

By understanding and implementing these concepts, you’ll be able to effectively manage CSV files in C# and use them for a variety of applications.