Console.ReadLine Method ()
Reads the next line of characters from the standard input stream.
Assembly: mscorlib (in mscorlib.dll)
Themethod reads a line from the standard input stream. (For the definition of a line, see the paragraph after the following list.) This means that:
If the standard input device is the keyboard, themethod blocks until the user presses the Enter key.
One of the most common uses of themethod is to pause program execution before clearing the console and displaying new information to it, or to prompt the user to press the Enter key before terminating the application. The following example illustrates this.
If standard input is redirected to a file, themethod reads a line of text from a file. For example, the following is a text file named ReadLine1.txt:
This is the first line. This is the second line. This is the third line. This is the fourth line.
The following example uses themethod to read input that is redirected from a file. The read operation terminates when the method returns null, which indicates that no lines remain to be read.
After compiling the example to an executable named ReadLine1.exe, you can run it from the command line with the syntax
ReadLine1 < ReadLine1.txt
to read the contents of the file and display them to the console.
A line is defined as a sequence of characters followed by a carriage return (hexadecimal 0x000d), a line feed (hexadecimal 0x000a), or the value of the Environment.NewLine property. The returned string does not contain the terminating character(s). By default, the method reads input from a 256-character input buffer. Because this includes the Environment.NewLine character(s), the method can read lines that contain up to 254 characters. To read longer lines, call the OpenStandardInput(Int32) method.
The In property returns a TextReader object that represents the standard input stream and that has both a synchronous TextReader.ReadLine method and an asynchronous TextReader.ReadLineAsync method. However, when used as the console's standard input stream, the TextReader.ReadLineAsync executes synchronously rather than asynchronously and returns a Task<String> only after the read operation has completed.method executes synchronously. That is, it blocks until a line is read or the Ctrl+Z keyboard combination is pressed. The
If this method throws an OutOfMemoryException exception, the reader's position in the underlying Stream object is advanced by the number of characters the method was able to read, but the characters already read into the internal buffer are discarded. Since the position of the reader in the stream cannot be changed, the characters already read are unrecoverable, and can be accessed only by reinitializing the TextReader. If the initial position within the stream is unknown or the stream does not support seeking, the underlying Stream also needs to be reinitialized. To avoid such a situation and to produce robust code, you should use the KeyAvailable property and ReadKey method and store the read characters in a pre-allocated buffer.
If the Ctrl+Z character is pressed when the method is reading input from the console, the method returns null. This enables the user to prevent further keyboard input when themethod is called in a loop. The following example illustrates this scenario.
The following example requires two command line arguments: the name of an existing text file, and the name of a file to write the output to. It opens the existing text file and redirects the standard input from the keyboard to that file. It also redirects the standard output from the console to the output file. It then uses the Console.WriteLine method to write the result to the output file.method to read each line in the file, replaces every sequence of four spaces with a tab character, and uses the
Available since 1.1
Available since 2.0
Windows Phone Silverlight
Available since 7.0