แก้ไข

แชร์ผ่าน


File.ReadAllText Method

Definition

Opens a text file, reads all the text in the file into a string, and then closes the file.

Overloads

ReadAllText(String)

Opens a text file, reads all the text in the file, and then closes the file.

ReadAllText(String, Encoding)

Opens a file, reads all text in the file with the specified encoding, and then closes the file.

ReadAllText(String)

Source:
File.cs
Source:
File.cs
Source:
File.cs

Opens a text file, reads all the text in the file, and then closes the file.

public:
 static System::String ^ ReadAllText(System::String ^ path);
public static string ReadAllText (string path);
static member ReadAllText : string -> string
Public Shared Function ReadAllText (path As String) As String

Parameters

path
String

The file to open for reading.

Returns

A string containing all the text in the file.

Exceptions

.NET Framework and .NET Core versions older than 2.1: path is a zero-length string, contains only white space, or contains one or more invalid characters. You can query for invalid characters by using the GetInvalidPathChars() method.

path is null.

The specified path, file name, or both exceed the system-defined maximum length.

The specified path is invalid (for example, it is on an unmapped drive).

An I/O error occurred while opening the file.

path specified a file that is read-only.

-or-

This operation is not supported on the current platform.

-or-

path specified a directory.

-or-

The caller does not have the required permission.

The file specified in path was not found.

path is in an invalid format.

The caller does not have the required permission.

Examples

The following code example demonstrates the use of the ReadAllText method to display the contents of a file. In this example a file is created, if it doesn't already exist, and text is added to it.

using System;
using System.IO;
using System.Text;

class Test
{
    public static void Main()
    {
        string path = @"c:\temp\MyTest.txt";

        // This text is added only once to the file.
        if (!File.Exists(path))
        {
            // Create a file to write to.
            string createText = "Hello and Welcome" + Environment.NewLine;
            File.WriteAllText(path, createText);
        }

        // This text is always added, making the file longer over time
        // if it is not deleted.
        string appendText = "This is extra text" + Environment.NewLine;
        File.AppendAllText(path, appendText);

        // Open the file to read from.
        string readText = File.ReadAllText(path);
        Console.WriteLine(readText);
    }
}
open System
open System.IO

let path = @"c:\temp\MyTest.txt"

// This text is added only once to the file.
if File.Exists path |> not then
    // Create a file to write to.
    let createText =
        "Hello and Welcome" + Environment.NewLine

    File.WriteAllText(path, createText)

// This text is always added, making the file longer over time
// if it is not deleted.
let appendText =
    "This is extra text" + Environment.NewLine

File.AppendAllText(path, appendText)

// Open the file to read from.
let readText = File.ReadAllText path
printfn $"{readText}"
Imports System.IO
Imports System.Text

Public Class Test
    Public Shared Sub Main()
        Dim path As String = "c:\temp\MyTest.txt"

        ' This text is added only once to the file.
        If File.Exists(path) = False Then

            ' Create a file to write to.
            Dim createText As String = "Hello and Welcome" + Environment.NewLine
            File.WriteAllText(path, createText)
        End If

        ' This text is always added, making the file longer over time
        ' if it is not deleted.
        Dim appendText As String = "This is extra text" + Environment.NewLine
        File.AppendAllText(path, appendText)

        ' Open the file to read from.
        Dim readText As String = File.ReadAllText(path)
        Console.WriteLine(readText)
    End Sub
End Class

Remarks

This method opens a file, reads all the text in the file, and returns it as a string. It then closes the file.

This method attempts to automatically detect the encoding of a file based on the presence of byte order marks. It automatically recognizes UTF-8, little-endian UTF-16, big-endian UTF-16, little-endian UTF-32, and big-endian UTF-32 text if the file starts with the appropriate byte order marks.

Use the ReadAllText(String, Encoding) method overload when reading files that might contain imported text, because unrecognized characters may not be read correctly.

The file handle is guaranteed to be closed by this method, even if exceptions are raised.

See also

Applies to

ReadAllText(String, Encoding)

Source:
File.cs
Source:
File.cs
Source:
File.cs

Opens a file, reads all text in the file with the specified encoding, and then closes the file.

public:
 static System::String ^ ReadAllText(System::String ^ path, System::Text::Encoding ^ encoding);
public static string ReadAllText (string path, System.Text.Encoding encoding);
static member ReadAllText : string * System.Text.Encoding -> string
Public Shared Function ReadAllText (path As String, encoding As Encoding) As String

Parameters

path
String

The file to open for reading.

encoding
Encoding

The encoding applied to the contents of the file.

Returns

A string containing all text in the file.

Exceptions

.NET Framework and .NET Core versions older than 2.1: path is a zero-length string, contains only white space, or contains one or more invalid characters. You can query for invalid characters by using the GetInvalidPathChars() method.

path is null.

The specified path, file name, or both exceed the system-defined maximum length.

The specified path is invalid (for example, it is on an unmapped drive).

An I/O error occurred while opening the file.

path specified a file that is read-only.

-or-

This operation is not supported on the current platform.

-or-

path specified a directory.

-or-

The caller does not have the required permission.

The file specified in path was not found.

path is in an invalid format.

The caller does not have the required permission.

Examples

The following code example demonstrates the use of the ReadAllText method to display the contents of a file. In this example a file is created, if it doesn't already exist, and text is added to it.

using System;
using System.IO;
using System.Text;

class Test
{
    public static void Main()
    {
        string path = @"c:\temp\MyTest.txt";

        // This text is added only once to the file.
        if (!File.Exists(path))
        {
            // Create a file to write to.
            string createText = "Hello and Welcome" + Environment.NewLine;
            File.WriteAllText(path, createText, Encoding.UTF8);
        }

        // This text is always added, making the file longer over time
        // if it is not deleted.
        string appendText = "This is extra text" + Environment.NewLine;
        File.AppendAllText(path, appendText, Encoding.UTF8);

        // Open the file to read from.
        string readText = File.ReadAllText(path);
        Console.WriteLine(readText);
    }
}
open System
open System.IO
open System.Text

let path = @"c:\temp\MyTest.txt"

// This text is added only once to the file.
if File.Exists path |> not then
    // Create a file to write to.
    let createText =
        "Hello and Welcome" + Environment.NewLine

    File.WriteAllText(path, createText, Encoding.UTF8)

// This text is always added, making the file longer over time
// if it is not deleted.
let appendText =
    "This is extra text" + Environment.NewLine

File.AppendAllText(path, appendText, Encoding.UTF8)

// Open the file to read from.
let readText = File.ReadAllText path
printfn $"{readText}"
Imports System.IO
Imports System.Text

Public Class Test
    Public Shared Sub Main()
        Dim path As String = "c:\temp\MyTest.txt"
        Dim sw As StreamWriter

        ' This text is added only once to the file.
        If File.Exists(path) = False Then

            ' Create a file to write to.
            Dim createText As String = "Hello and Welcome" + Environment.NewLine
            File.WriteAllText(path, createText, Encoding.UTF8)
        End If

        ' This text is always added, making the file longer over time
        ' if it is not deleted.
        Dim appendText As String = "This is extra text" + Environment.NewLine
        File.AppendAllText(path, appendText, Encoding.UTF8)

        ' Open the file to read from.
        Dim readText As String = File.ReadAllText(path)
        Console.WriteLine(readText)
    End Sub
End Class

Remarks

This method opens a file, reads all the text in the file, and returns it as a string. It then closes the file.

This method attempts to automatically detect the encoding of a file based on the presence of byte order marks. It automatically recognizes UTF-8, little-endian UTF-16, big-endian UTF-16, little-endian UTF-32, and big-endian UTF-32 text if the file starts with the appropriate byte order marks.

The file handle is guaranteed to be closed by this method, even if exceptions are raised.

To use the encoding settings as configured for your operating system, specify the Encoding.Default property for the encoding parameter.

See also

Applies to