private void Form1_Load(object sender, EventArgs e)
    {
        //Write a file
        string text = "The text inside the file.";
        System.IO.File.WriteAllText("file_name.txt", text);

        //Read a file
        string read = System.IO.File.ReadAllText("file_name.txt");
        MessageBox.Show(read); //Display text in the file
    }

除了文件。ReadAllText,文件。ReadAllLines和File。WriteAllText(和类似的帮助从文件类)显示在另一个答案，你可以使用StreamWriter/StreamReader类。

写入文本文件:

using(StreamWriter writetext = new StreamWriter("write.txt"))
{
    writetext.WriteLine("writing in text file");
}

读取文本文件:

using(StreamReader readtext = new StreamReader("readme.txt"))
{
   string readText = readtext.ReadLine();
}

注:

您可以使用readtext.Dispose()而不是using，但它不会在异常情况下关闭文件/读取器/写入器 请注意，相对路径是相对于当前工作目录。您可能希望使用/构造绝对路径。 缺少使用/Close是“为什么数据不写入文件”的常见原因。

     class Program
    { 
         public static void Main()
        { 
            //To write in a txt file
             File.WriteAllText("C:\\Users\\HP\\Desktop\\c#file.txt", "Hello and Welcome");

           //To Read from a txt file & print on console
             string  copyTxt = File.ReadAllText("C:\\Users\\HP\\Desktop\\c#file.txt");
             Console.Out.WriteLine("{0}",copyTxt);
        }      
    }

以下是最好的和最常用的文件读写方法:

using System.IO;

File.AppendAllText(sFilePathAndName, sTextToWrite);//add text to existing file
File.WriteAllText(sFilePathAndName, sTextToWrite);//will overwrite the text in the existing file. If the file doesn't exist, it will create it. 
File.ReadAllText(sFilePathAndName);

我在大学里学到的旧方法是使用流读取器/流写入器，但是文件I/O方法不那么笨重，需要的代码行也更少。您可以在IDE中键入“File.”(确保包含System. File.)。IO import语句)，并查看所有可用的方法。下面是使用Windows窗体应用程序从文本文件(.txt.)中读取/写入字符串的示例方法。

向现有文件追加文本:

private void AppendTextToExistingFile_Click(object sender, EventArgs e)
{
    string sTextToAppend = txtMainUserInput.Text;
    //first, check to make sure that the user entered something in the text box.
    if (sTextToAppend == "" || sTextToAppend == null)
    {MessageBox.Show("You did not enter any text. Please try again");}
    else
    {
        string sFilePathAndName = getFileNameFromUser();// opens the file dailog; user selects a file (.txt filter) and the method returns a path\filename.txt as string.
        if (sFilePathAndName == "" || sFilePathAndName == null)
        {
            //MessageBox.Show("You cancalled"); //DO NOTHING
        }
        else 
        {
            sTextToAppend = ("\r\n" + sTextToAppend);//create a new line for the new text
            File.AppendAllText(sFilePathAndName, sTextToAppend);
            string sFileNameOnly = sFilePathAndName.Substring(sFilePathAndName.LastIndexOf('\\') + 1);
            MessageBox.Show("Your new text has been appended to " + sFileNameOnly);
        }//end nested if/else
    }//end if/else

}//end method AppendTextToExistingFile_Click

通过文件资源管理器/打开文件对话框从用户获取文件名(您将需要这个来选择现有文件)。

private string getFileNameFromUser()//returns file path\name
{
    string sFileNameAndPath = "";
    OpenFileDialog fd = new OpenFileDialog();
    fd.Title = "Select file";
    fd.Filter = "TXT files|*.txt";
    fd.InitialDirectory = Environment.CurrentDirectory;
    if (fd.ShowDialog() == DialogResult.OK)
    {
        sFileNameAndPath = (fd.FileName.ToString());
    }
    return sFileNameAndPath;
}//end method getFileNameFromUser

从现有文件中获取文本:

private void btnGetTextFromExistingFile_Click(object sender, EventArgs e)
{
    string sFileNameAndPath = getFileNameFromUser();
    txtMainUserInput.Text = File.ReadAllText(sFileNameAndPath); //display the text
}

FileStream fs = new FileStream(txtSourcePath.Text,FileMode.Open, FileAccess.Read);
using(StreamReader sr = new StreamReader(fs))
{
   using (StreamWriter sw = new StreamWriter(Destination))
   {
            sw.Writeline("Your text");
    }
}

从文件中读取并写入文件的最简单方法:

//Read from a file
string something = File.ReadAllText("C:\\Rfile.txt");

//Write to a file
using (StreamWriter writer = new StreamWriter("Wfile.txt"))
{
    writer.WriteLine(something);
}