Console.ReadLine 方法
定义
重要
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从标准输入流中读取下一行字符。
public:
static System::String ^ ReadLine();[System.Runtime.Versioning.UnsupportedOSPlatform("android")]
[System.Runtime.Versioning.UnsupportedOSPlatform("browser")]
public static string? ReadLine();[System.Runtime.Versioning.UnsupportedOSPlatform("browser")]
public static string? ReadLine();public static string ReadLine();[<System.Runtime.Versioning.UnsupportedOSPlatform("android")>]
[<System.Runtime.Versioning.UnsupportedOSPlatform("browser")>]
static member ReadLine : unit -> string[<System.Runtime.Versioning.UnsupportedOSPlatform("browser")>]
static member ReadLine : unit -> stringstatic member ReadLine : unit -> stringPublic Shared Function ReadLine () As String返回
输入流中的下一行字符，或者 null 如果没有更多行可用。
- 属性
例外
出现 I/O 错误。
内存不足，无法为返回的字符串分配缓冲区。
下一行字符中的字符数大于 Int32.MaxValue。
示例
以下示例需要两个命令行参数：现有文本文件的名称以及要向其写入输出的文件的名称。 它将打开现有的文本文件，并将标准输入从键盘重定向到该文件。 它还会将标准输出从控制台重定向到输出文件。 然后，它使用 Console.ReadLine 该方法读取文件中的每一行，将四个空格的每个序列替换为制表符，并使用 Console.WriteLine 该方法将结果写入输出文件。
using System;
using System.IO;
public class InsertTabs
{
private const int tabSize = 4;
private const string usageText = "Usage: INSERTTABS inputfile.txt outputfile.txt";
public static int Main(string[] args)
{
if (args.Length < 2)
{
Console.WriteLine(usageText);
return 1;
}
try
{
// Attempt to open output file.
using (var writer = new StreamWriter(args[1]))
{
using (var reader = new StreamReader(args[0]))
{
// Redirect standard output from the console to the output file.
Console.SetOut(writer);
// Redirect standard input from the console to the input file.
Console.SetIn(reader);
string line;
while ((line = Console.ReadLine()) != null)
{
string newLine = line.Replace(("").PadRight(tabSize, ' '), "\t");
Console.WriteLine(newLine);
}
}
}
}
catch(IOException e)
{
TextWriter errorWriter = Console.Error;
errorWriter.WriteLine(e.Message);
errorWriter.WriteLine(usageText);
return 1;
}
// Recover the standard output stream so that a
// completion message can be displayed.
var standardOutput = new StreamWriter(Console.OpenStandardOutput());
standardOutput.AutoFlush = true;
Console.SetOut(standardOutput);
Console.WriteLine($"INSERTTABS has completed the processing of {args[0]}.");
return 0;
}
}
open System
open System.IO
let tabSize = 4
let usageText = "Usage: INSERTTABS inputfile.txt outputfile.txt"
[<EntryPoint>]
let main args =
if args.Length < 2 then
Console.WriteLine usageText
1
else
try
// Attempt to open output file.
use reader = new StreamReader(args[0])
use writer = new StreamWriter(args[1])
// Redirect standard output from the console to the output file.
Console.SetOut writer
// Redirect standard input from the console to the input file.
Console.SetIn reader
let mutable line = Console.ReadLine()
while line <> null do
let newLine = line.Replace(("").PadRight(tabSize, ' '), "\t")
Console.WriteLine newLine
line <- Console.ReadLine()
// Recover the standard output stream so that a
// completion message can be displayed.
let standardOutput = new StreamWriter(Console.OpenStandardOutput())
standardOutput.AutoFlush <- true
Console.SetOut standardOutput
Console.WriteLine $"INSERTTABS has completed the processing of {args[0]}."
0
with :? IOException as e ->
let errorWriter = Console.Error
errorWriter.WriteLine e.Message
errorWriter.WriteLine usageText
1
Imports System.IO
Public Module InsertTabs
Private Const tabSize As Integer = 4
Private Const usageText As String = "Usage: INSERTTABS inputfile.txt outputfile.txt"
Public Function Main(args As String()) As Integer
If args.Length < 2 Then
Console.WriteLine(usageText)
Return 1
End If
Try
' Attempt to open output file.
Using writer As New StreamWriter(args(1))
Using reader As New StreamReader(args(0))
' Redirect standard output from the console to the output file.
Console.SetOut(writer)
' Redirect standard input from the console to the input file.
Console.SetIn(reader)
Dim line As String = Console.ReadLine()
While line IsNot Nothing
Dim newLine As String = line.Replace("".PadRight(tabSize, " "c), ControlChars.Tab)
Console.WriteLine(newLine)
line = Console.ReadLine()
End While
End Using
End Using
Catch e As IOException
Dim errorWriter As TextWriter = Console.Error
errorWriter.WriteLine(e.Message)
errorWriter.WriteLine(usageText)
Return 1
End Try
' Recover the standard output stream so that a
' completion message can be displayed.
Dim standardOutput As New StreamWriter(Console.OpenStandardOutput())
standardOutput.AutoFlush = True
Console.SetOut(standardOutput)
Console.WriteLine($"INSERTTABS has completed the processing of {args(0)}.")
Return 0
End Function
End Module
注解
该方法 ReadLine 从标准输入流中读取一行。 （有关行的定义，请参阅以下列表后面的段落。这意味着：
如果标准输入设备是键盘，方法 ReadLine 将阻止，直到用户按下 Enter 键。
该方法的最常见用途 ReadLine 之一是在清除控制台并显示新信息之前暂停程序执行，或提示用户在终止应用程序之前按 Enter 键。 下面的示例对此进行了演示。
using System; public class Example { public static void Main() { Console.Clear(); DateTime dat = DateTime.Now; Console.WriteLine("\nToday is {0:d} at {0:T}.", dat); Console.Write("\nPress any key to continue... "); Console.ReadLine(); } } // The example displays output like the following: // Today is 10/26/2015 at 12:22:22 PM. // // Press any key to continue...open System Console.Clear() let dat = DateTime.Now printfn $"\nToday is {dat:d} at {dat:T}." printf "\nPress any key to continue... " Console.ReadLine() |> ignore // The example displays output like the following: // Today is 12/28/2021 at 8:23:50 PM. // // Press any key to continue...Module Example Public Sub Main() Console.Clear() Dim dat As Date = Date.Now Console.WriteLine() Console.WriteLine("Today is {0:d} at {0:T}.", dat) Console.WriteLine() Console.Write("Press any key to continue... ") Console.ReadLine() End Sub End Module ' The example displays output like the following: ' Today is 10/26/2015 at 12:22:22 PM. ' ' Press any key to continue...如果标准输入重定向到文件，该方法 ReadLine 将从文件中读取一行文本。 例如，下面是一个名为 ReadLine1.txt的文本文件：
This is the first line. This is the second line. This is the third line. This is the fourth line.以下示例使用 ReadLine 该方法读取从文件重定向的输入。 当方法返回
null时，读取操作将终止，这表示没有要读取的行。using System; public class Example { public static void Main() { if (!Console.IsInputRedirected) { Console.WriteLine("This example requires that input be redirected from a file."); return; } Console.WriteLine("About to call Console.ReadLine in a loop."); Console.WriteLine("----"); String s; int ctr = 0; do { ctr++; s = Console.ReadLine(); Console.WriteLine("Line {0}: {1}", ctr, s); } while (s != null); Console.WriteLine("---"); } } // The example displays the following output: // About to call Console.ReadLine in a loop. // ---- // Line 1: This is the first line. // Line 2: This is the second line. // Line 3: This is the third line. // Line 4: This is the fourth line. // Line 5: // ---open System if not Console.IsInputRedirected then printfn "This example requires that input be redirected from a file." printfn "About to call Console.ReadLine in a loop." printfn "----" let mutable s = "" let mutable i = 0 while s <> null do i <- i + 1 s <- Console.ReadLine() printfn $"Line {i}: {s}" printfn "---" // The example displays the following output: // About to call Console.ReadLine in a loop. // ---- // Line 1: This is the first line. // Line 2: This is the second line. // Line 3: This is the third line. // Line 4: This is the fourth line. // Line 5: // ---Module Example Public Sub Main() If Not Console.IsInputRedirected Then Console.WriteLine("This example requires that input be redirected from a file.") Exit Sub End If Console.WriteLine("About to call Console.ReadLine in a loop.") Console.WriteLine("----") Dim s As String Dim ctr As Integer Do ctr += 1 s = Console.ReadLine() Console.WriteLine("Line {0}: {1}", ctr, s) Loop While s IsNot Nothing Console.WriteLine("---") End Sub End Module ' The example displays the following output: ' About to call Console.ReadLine in a loop. ' ---- ' Line 1: This is the first line. ' Line 2: This is the second line. ' Line 3: This is the third line. ' Line 4: This is the fourth line. ' Line 5: ' ---将示例编译为名为 ReadLine1.exe的可执行文件后，可以从命令行运行它，以读取文件的内容并将其显示到控制台。 语法为：
ReadLine1 < ReadLine1.txt
行定义为后跟回车符（十六进制0x000d）、换行符（十六进制0x000a）或属性的值的 Environment.NewLine 序列。 返回的字符串不包含终止字符（s）。 默认情况下，该方法从 256 个字符的输入缓冲区读取输入。 由于这包括 Environment.NewLine 字符（s），因此该方法可以读取最多包含 254 个字符的行。 若要读取较长的行，请调用 OpenStandardInput(Int32) 该方法。
该方法 ReadLine 同步执行。 也就是说，在读取行或 按 Ctrl+Z 键盘组合（后跟 Windows 上的 Enter ）之前，它会阻止它。 该 In 属性返回一个 TextReader 对象，该对象表示标准输入流，并且同时具有同步 TextReader.ReadLine 方法和异步 TextReader.ReadLineAsync 方法。 但是，当用作控制台的标准输入流时，同步 TextReader.ReadLineAsync 执行而不是异步执行，并且仅在读取操作完成后返回 Task<String> 。
如果此方法引发 OutOfMemoryException 异常，则方法能够读取的字符数会高级读取器在基础 Stream 对象中的位置，但已读入内部 ReadLine 缓冲区的字符将被丢弃。 由于无法更改流中读取器的位置，因此已读取的字符不可恢复，并且只能通过重新初始化来 TextReader访问。 如果流中的初始位置未知或流不支持查找， Stream 则基础还需要重新初始化。 为了避免这种情况并生成可靠的代码，应使用 KeyAvailable 属性和 ReadKey 方法并将读取字符存储在预分配的缓冲区中。
如果在从控制台读取输入时按下 Ctrl+Z 组合键（后跟 Windows 上的 Enter ），该方法将 null返回。 这使用户能够在循环中调用该方法时 ReadLine 防止进一步的键盘输入。 以下示例对此情况进行了说明。
using System;
public class Example
{
public static void Main()
{
string line;
Console.WriteLine("Enter one or more lines of text (press CTRL+Z to exit):");
Console.WriteLine();
do {
Console.Write(" ");
line = Console.ReadLine();
if (line != null)
Console.WriteLine(" " + line);
} while (line != null);
}
}
// The following displays possible output from this example:
// Enter one or more lines of text (press CTRL+Z to exit):
//
// This is line #1.
// This is line #1.
// This is line #2
// This is line #2
// ^Z
//
// >
open System
printfn "Enter one or more lines of text (press CTRL+Z to exit):\n"
let mutable line = ""
while line <> null do
printf " "
line <- Console.ReadLine()
if line <> null then
printfn $" {line}"
// The following displays possible output from this example:
// Enter one or more lines of text (press CTRL+Z to exit):
//
// This is line #1.
// This is line #1.
// This is line #2
// This is line #2
// ^Z
//
// >
Module Example
Public Sub Main()
Dim line As String
Console.WriteLine("Enter one or more lines of text (press CTRL+Z to exit):")
Console.WriteLine()
Do
Console.Write(" ")
line = Console.ReadLine()
If line IsNot Nothing Then Console.WriteLine(" " + line)
Loop While line IsNot Nothing
End Sub
End Module
' The following displays possible output from this example:
' Enter one or more lines of text (press CTRL+Z to exit):
'
' This is line #1.
' This is line #1.
' This is line #2
' This is line #2
' ^Z
'
' >
