Working with Files in C#

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C # contains the static file class for performing I/O operations on the physical file system. The static file class contains several functions for interacting with, for example, a physical file of any type. binary, text, etc.

The File class comes under the System.IO namespace. Let's discuss some examples of File Class.

Append Text Lines

In C# for append multiple text lines in a file, there's a method File.AppendLine().

string sampleText = "This is first line. \n This is second line. \nThis is third line.";
// If the file does not exist then create and open the file and append lines.
// If the file exists then Open the file and append lines.
File.AppendAllLines(@"E:\Example.txt", sampleText.Split(Environment.NewLine.ToCharArray()).ToList<string>());

Output:

Append String

In C# for append a line of string in the file there's a method File.AppendAllText();

// If the file does not exist then create and open the file and append text.
// If the file exists then Open the file and append text.
File.AppendAllText(@"E:\Example.txt", "New Text");

Output:

Overwrite Text

To remove the existing text and overwrite new text in the file there's a method File.WriteAllText();

// If the file does not exist then create and open the file and  write text.
// If the file exists then Open the file and write text.
File.WriteAllText(@"E:\Example.txt", "Remove All the previous Text");

Output:

Other Methods with Example

//Copy an existing file to a new file.
File.Copy(@"C:\Example.txt", @"D:\Newfile.txt");

//Get the file last accessed last time 
DateTime lastAccessTime = File.GetLastAccessTime(@"C:\Example.txt");

//Get when the file was written last time
DateTime lastWriteTime = File.GetLastWriteTime(@"C:\Example.txt");

// Move a specified file to new location
File.Move(@"C:\Example.txt", @"D:\Example.txt");

//Opens a File and returns FileStream
FileStream fs = File.Open(@"D:\Example.txt", FileMode.OpenOrCreate);

//Opens a file and return StreamReader
StreamReader sr = File.OpenText(@"D:\Example.txt");

//To check whether file is exists or not
bool isFileExists = File.Exists(@"C:\ Example.txt"); // returns false

//Delete a file
File.Delete(@"C:\Example.txt");

Some Important Methods in C# File Class

Method Usage
AppendLine Appends lines to a file, and then closes the file. If the specified file does not exist, this method creates a file, writes the specified lines to the file, and then closes the file.
AppendAllLines Appends lines to a file by using a specified encoding, and then closes the file. If the specified file does not exist, this method creates a file, writes the specified lines to the file, and then closes the file.
AppendAllLinesAsync Asynchronously appends lines to a file, and then closes the file. If the specified file does not exist, this method creates a file, writes the specified lines to the file, and then closes the file.
AppendAllText Opens a file, appends the specified string to the file, and then closes the file. If the file does not exist, this method creates a file, writes the specified string to the file, then closes the file.
AppendAllTextAsync Asynchronously opens a file or creates a file if it does not already exist, appends the specified string to the file, and then closes the file.
AppendText Creates a StreamWriter that appends UTF-8 encoded text to an existing file, or to a new file if the specified file does not exist.
Copy Copies an existing file to a new file. Overwriting a file of the same name is not allowed.
Create Creates or overwrites a file in the specified path.
Move Moves a specified file to a new location, providing the option to specify a new file name.
Open Opens a FileStream on the specified path with read/write access with no sharing.
OpenText Opens an existing UTF-8 encoded text file for reading.
OpenWrite Opens an existing file or creates a new file for writing.
ReadAllLines Opens a text file, reads all lines of the file, and then closes the file.
Replace Replaces the contents of a specified file with the contents of another file, deleting the original file, and creating a backup of the replaced file.
WriteAllText Creates a new file, writes the specified string to the file, and then closes the file. If the target file already exists, it is overwritten.
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