File.ReadAllLines(String) Method in C# with Examples

File.ReadAllLines(String) is an inbuilt File class method that is used to open a text file then reads all lines of the file into a string array and then closes the file.

Syntax:

public static string[] ReadAllLines (string path);

Parameter: This function accepts a parameter which is illustrated below:

  • path: This is the specified file to open for reading.

Exceptions:

  • ArgumentException: The path is a zero-length string, contains only white space, or one or more invalid characters as defined by InvalidPathChars.
  • ArgumentNullException: The path is null.
  • PathTooLongException: The specified path, file name, or both exceed the system-defined maximum length.
  • DirectoryNotFoundException: The specified path is invalid.
  • IOException: An I/O error occurred while opening the file.
  • UnauthorizedAccessException: The path specified a file that is read-only. OR this operation is not supported on the current platform. OR the path specified a directory. OR the caller does not have the required permission.
  • FileNotFoundException: The file specified in the path was not found.
  • NotSupportedException: The path is in an invalid format.
  • SecurityException: The caller does not have the required permission.

Return Value: Returns a string array containing all lines of the file.



Below are the programs to illustrate the File.ReadAllLines(String) method.

Program 1: Initially, a file file.txt is created with some contents shown below-

file.txt

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// C# program to illustrate the usage
// of File.ReadAllLines(String) method
  
// Using System, System.IO and
// System.Text namespaces
using System;
using System.IO;
using System.Text;
  
class GFG {
    public static void Main()
    {
        // Specifing a file
        string path = @"file.txt";
  
        // Calling the ReadAllLines() function
        string[] readText = File.ReadAllLines(path);
        foreach(string s in readText)
        {
            // Printing the string array containing
            // all lines of the file.
            Console.WriteLine(s);
        }
    }
}

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Output:

GFG
Geeks
GeeksforGeeks

Program 2: Initially, no file was created. Below code itself create a file file.txt with some specified contents.

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// C# program to illustrate the usage
// of File.ReadAllLines(String) method
  
// Using System, System.IO and
// System.Text namespaces
using System;
using System.IO;
using System.Text;
  
class GFG {
    public static void Main()
    {
        // Specifing a file
        string path = @"file.txt";
  
        // Adding below contents to the file
        string[] createText = { "GFG is a CS portal." };
        File.WriteAllLines(path, createText);
  
        // Calling the ReadAllLines() function
        string[] readText = File.ReadAllLines(path);
        foreach(string s in readText)
        {
            // Printing the string array containing
            // all lines of the file.
            Console.WriteLine(s);
        }
    }
}

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Output:

GFG is a CS portal.



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