//引入命名空间
using System;
using System.IO;

class Test 
{
    public static void Main() 
    {
        try 
        {
            // Create an instance of StreamReader to read from a file.
            // The using statement also closes the StreamReader.
            using (StreamReader sr = new StreamReader("TestFile.txt")) 
            {
                string line;
                // Read and display lines from the file until the end of 
                // the file is reached.
                while ((line = sr.ReadLine()) != null) 
                {
                    Console.WriteLine(line);
                }
            }
        }
        catch (Exception e) 
        {
            // Let the user know what went wrong.
            Console.WriteLine("The file could not be read:");
            Console.WriteLine(e.Message);
        }
    }
}

//引入命名空间
using System;
using System.IO;
using System.Threading.Tasks;

class Example
{
    static async Task Main()
    {
        await ReadAndDisplayFilesAsync();
    }

    static async Task ReadAndDisplayFilesAsync()
    {
        String filename = "TestFile1.txt";
        Char[] buffer;
        
        using (var sr = new StreamReader(filename)) {
            buffer = new Char[(int)sr.BaseStream.Length];
            await sr.ReadAsync(buffer, 0, (int)sr.BaseStream.Length);
        }

        Console.WriteLine(new String(buffer));
    }
}

//引入命名空间
using System;
using System.IO;

class MainClass {
    public static void Main(string[] args) {
        try {
            FileStream fs = new FileStream("c:\\a.txt", FileMode.Open);
            StreamReader sr = new StreamReader(fs);

            string line = "";

            int lineNo = 0;
            do {
                line = sr.ReadLine();
                if (line != null) {
                    Console.WriteLine("{0}: {1}", lineNo, line);
                    lineNo++;
                }
            } while (line != null);
        } catch (Exception e) {
            Console.WriteLine("Exception in ShowFile: {0}", e);
        }
    }
}