c#读取写入文本文件

读取文本文件：

class ReadFromFile
{
    static void Main()
    {
        // The files used here were created in the code example
        // in How to: Write to a Text File. You can of course substitute
        // other files of your own.

        // Example #1
        // Read the file as one string.
        string text = System.IO.File.ReadAllText(@"filename");

        // Display the file contents to the console.
        System.Console.WriteLine("Contents of writeText.txt = {0}", text);

        // Example #2
        // Read the file lines into a string array.
        string[] lines = System.IO.File.ReadAllLines(@"filename");            

        System.Console.WriteLine("Contents of writeLines2.txt =:");
        foreach (string line in lines)
        {
            Console.WriteLine("\t" + line);
        }

        // Keep the console window open in debug mode.
        Console.WriteLine("Press any key to exit.");
        System.Console.ReadKey();
    }
} 

一次读取一行文本文件

int counter = 0;
string line;

// Read the file and display it line by line.
System.IO.StreamReader file =
    new System.IO.StreamReader(@"c:\test.txt");
while((line = file.ReadLine()) != null)
{
    System.Console.WriteLine (line);
    counter++;
}

file.Close();
System.Console.WriteLine("There were {0} lines.", counter);
// Suspend the screen.
System.Console.ReadLine();

写入文本文件：

        以下示例给出了将文本写入文件的各种方法。前两个示例使用 System.IO..::.File 类中的静态方法将完整的字符串数组或完整字符串写入文本文件。示例 #3 说明如果在将文本写入文件之前必须分别处理文本的每一行，应该如何将这些文本添加到文件中。示例 1-3 均覆盖文件中的所有现有内容。示例 #4 说明如何将文本追加到现有文件的末尾。

class WriteTextFile
{
    static void Main()
    {

 // These examples assume a "C:\Users\Public\TestFolder" folder on your

 machine.
        // You can modify the path if necessary.

        // Example #1: Write an array of strings to a file.
        // Create a string array that consists of three lines.
        string[] lines = {"First line", "Second line", "Third line"};
        System.IO.File.WriteAllLines(@"filename", lines);

        // Example #2: Write one string to a text file.
        string text = "A class is the most powerful data type in C#. 

 Like structures, " +
                "a class defines the data and behavior of the data type. ";
        System.IO.File.WriteAllText(@"filename", text);

        // Example #3: Write only some strings in an array to a file.
        using (System.IO.StreamWriter file = 

new System.IO.StreamWriter(@"filename"))
        {
            foreach (string line in lines)
            {
                if (line.Contains("Second") == false)
                {
                    file.WriteLine(line);
                }
            }
        }

        // Example #4: Append new text to an existing fileusing 

(System.IO.StreamWriter file = new System.IO.StreamWriter(@"filename", true))
        {
            file.WriteLine("Fourth line");
        }
    }
}
/* Output (to WriteLines.txt):
    First line
    Second line
    Third line

 Output (to WriteText.txt):
    A class is the most powerful data type in C#. Like structures, a class

 defines the data and behavior of the data type.

 Output to WriteLines2.txt after Example #3:
    First line
    Third line

 Output to WriteLines2.txt after Example #4:
    First line
    Third line
    Fourth line
 */