MemoryMappedFile.OpenExisting Method

Definition

Namespace:

System.IO.MemoryMappedFiles

Assembly:

System.IO.MemoryMappedFiles.dll

Opens an existing named memory-mapped file in system memory.

Overloads

OpenExisting(String)	Opens an existing memory-mapped file that has the specified name in system memory.
OpenExisting(String, MemoryMappedFileRights)	Opens an existing memory-mapped file that has the specified name and access rights in system memory.
OpenExisting(String, MemoryMappedFileRights, HandleInheritability)	Opens an existing memory-mapped file that has the specified name, access rights, and inheritability in system memory.

OpenExisting(String)

Source:

MemoryMappedFile.cs

Opens an existing memory-mapped file that has the specified name in system memory.

public:
 static System::IO::MemoryMappedFiles::MemoryMappedFile ^ OpenExisting(System::String ^ mapName);

[System.Runtime.Versioning.SupportedOSPlatform("windows")]
public static System.IO.MemoryMappedFiles.MemoryMappedFile OpenExisting (string mapName);

[<System.Runtime.Versioning.SupportedOSPlatform("windows")>]
static member OpenExisting : string -> System.IO.MemoryMappedFiles.MemoryMappedFile

Public Shared Function OpenExisting (mapName As String) As MemoryMappedFile

Parameters

mapName

String

The name of the memory-mapped file.

Returns

MemoryMappedFile

A memory-mapped file that has the specified name.

Attributes

SupportedOSPlatformAttribute

Exceptions

ArgumentNullException

mapName is null.

ArgumentException

mapName is an empty string.

FileNotFoundException

The file specified for mapName does not exist.

Examples

Opening a Persisted Memory-Mapped File

The following example opens a memory-mapped file named ImgA that has already been created from a file on disk (as shown in the example for the CreateFromFile(String) method).

using System;
using System.IO.MemoryMappedFiles;
using System.Runtime.InteropServices;

class Program
{
    static void Main(string[] args)
    {
        // Assumes another process has created the memory-mapped file.
        using (var mmf = MemoryMappedFile.OpenExisting("ImgA"))
        {
            using (var accessor = mmf.CreateViewAccessor(4000000, 2000000))
            {
                int colorSize = Marshal.SizeOf(typeof(MyColor));
                MyColor color;

                // Make changes to the view.
                for (long i = 0; i < 1500000; i += colorSize)
                {
                    accessor.Read(i, out color);
                    color.Brighten(20);
                    accessor.Write(i, ref color);
                }
            }
        }
    }
}

public struct MyColor
{
    public short Red;
    public short Green;
    public short Blue;
    public short Alpha;

    // Make the view brigher.
    public void Brighten(short value)
    {
        Red = (short)Math.Min(short.MaxValue, (int)Red + value);
        Green = (short)Math.Min(short.MaxValue, (int)Green + value);
        Blue = (short)Math.Min(short.MaxValue, (int)Blue + value);
        Alpha = (short)Math.Min(short.MaxValue, (int)Alpha + value);
    }
}

Imports System.IO.MemoryMappedFiles
Imports System.Runtime.InteropServices

Class Program
    Public Shared Sub Main(ByVal args As String())
        ' Assumes another process has created the memory-mapped file.
        Using mmf = MemoryMappedFile.OpenExisting("ImgA")
            Using accessor = mmf.CreateViewAccessor(4000000, 2000000)
                Dim colorSize As Integer = Marshal.SizeOf(GetType(MyColor))
                Dim color As MyColor

                ' Make changes to the view.
                Dim i As Long = 0
                While i < 1500000
                    accessor.Read(i, color)
                    color.Brighten(30)
                    accessor.Write(i, color)
                    i += colorSize
                End While
            End Using
        End Using
    End Sub
End Class

Public Structure MyColor
    Public Red As Short
    Public Green As Short
    Public Blue As Short
    Public Alpha As Short

    ' Make the view brigher.
    Public Sub Brighten(ByVal value As Short)
        Red = CShort(Math.Min(Short.MaxValue, CInt(Red) + value))
        Green = CShort(Math.Min(Short.MaxValue, CInt(Green) + value))
        Blue = CShort(Math.Min(Short.MaxValue, CInt(Blue) + value))
        Alpha = CShort(Math.Min(Short.MaxValue, CInt(Alpha) + value))
    End Sub
End Structure

Opening a Non-Persisted Memory-Mapped File

The following example opens a memory-mapped file used for inter-process communication. This code example is part of a larger example provided for the CreateNew(String, Int64) method.

Remarks

The memory-mapped file can be either a persisted memory-mapped file (associated with a file on disk) or non-persisted.

See also

• Memory-Mapped Files

OpenExisting(String, MemoryMappedFileRights)

Source:

MemoryMappedFile.cs

Opens an existing memory-mapped file that has the specified name and access rights in system memory.

public:
 static System::IO::MemoryMappedFiles::MemoryMappedFile ^ OpenExisting(System::String ^ mapName, System::IO::MemoryMappedFiles::MemoryMappedFileRights desiredAccessRights);

[System.Runtime.Versioning.SupportedOSPlatform("windows")]
public static System.IO.MemoryMappedFiles.MemoryMappedFile OpenExisting (string mapName, System.IO.MemoryMappedFiles.MemoryMappedFileRights desiredAccessRights);

[<System.Runtime.Versioning.SupportedOSPlatform("windows")>]
static member OpenExisting : string * System.IO.MemoryMappedFiles.MemoryMappedFileRights -> System.IO.MemoryMappedFiles.MemoryMappedFile

Public Shared Function OpenExisting (mapName As String, desiredAccessRights As MemoryMappedFileRights) As MemoryMappedFile

Parameters

mapName

String

The name of the memory-mapped file to open.

desiredAccessRights

MemoryMappedFileRights

One of the enumeration values that specifies the access rights to apply to the memory-mapped file.

Returns

MemoryMappedFile

A memory-mapped file that has the specified characteristics.

Attributes

SupportedOSPlatformAttribute

Exceptions

ArgumentNullException

mapName is null.

ArgumentException

mapName is an empty string.

ArgumentOutOfRangeException

desiredAccessRights is not a valid MemoryMappedFileRights enumeration value.

FileNotFoundException

The file specified for mapName does not exist.

See also

• Memory-Mapped Files

OpenExisting(String, MemoryMappedFileRights, HandleInheritability)

Source:

MemoryMappedFile.cs

Opens an existing memory-mapped file that has the specified name, access rights, and inheritability in system memory.

public:
 static System::IO::MemoryMappedFiles::MemoryMappedFile ^ OpenExisting(System::String ^ mapName, System::IO::MemoryMappedFiles::MemoryMappedFileRights desiredAccessRights, System::IO::HandleInheritability inheritability);

[System.Runtime.Versioning.SupportedOSPlatform("windows")]
public static System.IO.MemoryMappedFiles.MemoryMappedFile OpenExisting (string mapName, System.IO.MemoryMappedFiles.MemoryMappedFileRights desiredAccessRights, System.IO.HandleInheritability inheritability);

[<System.Runtime.Versioning.SupportedOSPlatform("windows")>]
static member OpenExisting : string * System.IO.MemoryMappedFiles.MemoryMappedFileRights * System.IO.HandleInheritability -> System.IO.MemoryMappedFiles.MemoryMappedFile

Public Shared Function OpenExisting (mapName As String, desiredAccessRights As MemoryMappedFileRights, inheritability As HandleInheritability) As MemoryMappedFile

Parameters

mapName

String

The name of the memory-mapped file to open.

desiredAccessRights

MemoryMappedFileRights

One of the enumeration values that specifies the access rights to apply to the memory-mapped file.

inheritability

HandleInheritability

One of the enumeration values that specifies whether a handle to the memory-mapped file can be inherited by a child process. The default is None.

Returns

MemoryMappedFile

A memory-mapped file that has the specified characteristics.

Attributes

SupportedOSPlatformAttribute

Exceptions

ArgumentNullException

mapName is null.

ArgumentException

mapName is an empty string.

ArgumentOutOfRangeException

desiredAccessRights is not a valid MemoryMappedFileRights enumeration value.

-or-

inheritability is not a valid HandleInheritability enumeration value.

UnauthorizedAccessException

The requested access is invalid for the memory-mapped file.

FileNotFoundException

The file specified for mapName does not exist.

See also

• Memory-Mapped Files