StreamWriter.WriteAsync Method

Definition

Namespace:

System.IO

Assemblies:

netstandard.dll, System.Runtime.dll

Asynchronously writes data to the stream.

Overloads

WriteAsync(Char)	Asynchronously writes a character to the stream.
WriteAsync(String)	Asynchronously writes a string to the stream.
WriteAsync(ReadOnlyMemory<Char>, CancellationToken)	Asynchronously writes a character memory region to the stream.
WriteAsync(Char[], Int32, Int32)	Asynchronously writes a subarray of characters to the stream.

WriteAsync(Char)

Source:

StreamWriter.cs

Asynchronously writes a character to the stream.

C#

public override System.Threading.Tasks.Task WriteAsync(char value);

Parameters

value

Char

The character to write to the stream.

Returns

Task

A task that represents the asynchronous write operation.

Exceptions

ObjectDisposedException

The stream writer is disposed.

InvalidOperationException

The stream writer is currently in use by a previous write operation.

Examples

The following example shows how to write a single character (the letter "a") to a text file by using the WriteAsync(Char) method.

C#

using System.IO;

namespace ConsoleApplication
{
    class Program1
    {
        static void Main()
        {
            WriteCharacters();
        }

        static async void WriteCharacters()
        {
            using (StreamWriter writer = File.CreateText("newfile.txt"))
            {
                await writer.WriteAsync('a');
            }
        }
    }
}

Remarks

This method stores in the task it returns all non-usage exceptions that the method's synchronous counterpart can throw. If an exception is stored into the returned task, that exception will be thrown when the task is awaited. Usage exceptions, such as ArgumentException, are still thrown synchronously. For the stored exceptions, see the exceptions thrown by Write(Char).

WriteAsync(String)

Source:

StreamWriter.cs

Asynchronously writes a string to the stream.

C#

public override System.Threading.Tasks.Task WriteAsync(string? value);

Parameters

value

String

The string to write to the stream. If value is null, nothing is written.

Returns

Task

A task that represents the asynchronous write operation.

Exceptions

ObjectDisposedException

The stream writer is disposed.

InvalidOperationException

The stream writer is currently in use by a previous write operation.

Examples

The following example shows how to write a string to a text file by using the WriteAsync(String) method.

C#

using System.IO;

namespace ConsoleApplication
{
    class Program2
    {
        static void Main()
        {
            WriteCharacters();
        }

        static async void WriteCharacters()
        {
            using (StreamWriter writer = File.CreateText("newfile.txt"))
            {
                await writer.WriteAsync("Example text as string");
            }
        }
    }
}

Remarks

This method stores in the task it returns all non-usage exceptions that the method's synchronous counterpart can throw. If an exception is stored into the returned task, that exception will be thrown when the task is awaited. Usage exceptions, such as ArgumentException, are still thrown synchronously. For the stored exceptions, see the exceptions thrown by Write(String).

WriteAsync(ReadOnlyMemory<Char>, CancellationToken)

Source:

StreamWriter.cs

Asynchronously writes a character memory region to the stream.

C#

public override System.Threading.Tasks.Task WriteAsync(ReadOnlyMemory<char> buffer, System.Threading.CancellationToken cancellationToken = default);

Parameters

buffer

ReadOnlyMemory<Char>

The character memory region to write to the stream.

cancellationToken

CancellationToken

The token to monitor for cancellation requests. The default value is None.

Returns

Task

A task that represents the asynchronous write operation.

Exceptions

OperationCanceledException

The cancellation token was canceled. This exception is stored into the returned task.

WriteAsync(Char[], Int32, Int32)

Source:

StreamWriter.cs

Asynchronously writes a subarray of characters to the stream.

C#

public override System.Threading.Tasks.Task WriteAsync(char[] buffer, int index, int count);

Parameters

buffer

Char[]

A character array that contains the data to write.

index

Int32

The character position in the buffer at which to begin reading data.

count

Int32

The maximum number of characters to write.

Returns

Task

A task that represents the asynchronous write operation.

Exceptions

ArgumentNullException

buffer is null.

ArgumentException

The index plus count is greater than the buffer length.

ArgumentOutOfRangeException

index or count is negative.

ObjectDisposedException

The stream writer is disposed.

InvalidOperationException

The stream writer is currently in use by a previous write operation.

Examples

The following example shows how to write multiple characters to a text file by using the WriteAsync(Char[], Int32, Int32) method.

C#

using System.IO;
using System.Text;

namespace ConsoleApplication
{
    class Program5
    {
        static void Main()
        {
            WriteCharacters();
        }

        static async void WriteCharacters()
        {
            UnicodeEncoding ue = new UnicodeEncoding();
            char[] charsToAdd = ue.GetChars(ue.GetBytes("Example string"));
            using (StreamWriter writer = File.CreateText("newfile.txt"))
            {
                await writer.WriteAsync(charsToAdd, 0, charsToAdd.Length);
            }
        }
    }
}

Remarks

This method stores in the task it returns all non-usage exceptions that the method's synchronous counterpart can throw. If an exception is stored into the returned task, that exception will be thrown when the task is awaited. Usage exceptions, such as ArgumentException, are still thrown synchronously. For the stored exceptions, see the exceptions thrown by Write(Char[], Int32, Int32).