MemoryStream

Implements:

Public:

Types:

Name	Description
BufferMode	The method a specified byte array should be referenced.

Properties:

Name	Description
CanRead (get)	Gets value indicating whether the current stream supports reading.
CanSeek (get)	Gets value indicating whether the current stream supports seeking.
CanTimeout (get)	Gets if the MemoryStream object supports timeout events.
CanWrite (get)	Gets value indicating whether the current stream supports writing.
Capacity (get)	Gets the number of bytes allocated for this stream.
Capacity (let)	Sets the number of bytes allocated for this stream.
Length (get)	Gets the length of the stream in bytes.
Position (get)	Returns the current position within the stream.
Position (let)	Sets the current position within the stream.
ReadTimeout (get)	Gets the timeout duration for a read operation.
ReadTimeout (let)	Sets the timeout duration for a read operation.
WriteTimeout (get)	Gets the timeout duration of a write operation.
WriteTimeout (let)	Sets the timeout duration for a write operation.

Methods:

Name	Description
BeginRead	Begins an asynchronous buffer read. For a MemoryStream, calling an asynchronous buffer read is identical to calling ReadBlock.
BeginWrite	Begins an asynchronous buffer write. For a MemoryStream, having an asynchronous buffer write is of no use.
CloseStream	Closes the MemoryStream and releases any resources allocated.
CopyTo	Reads the bytes from the current stream and writes them to another stream.
EndRead	Signifies the end of an asynchronous read from the stream.
EndWrite	Signifies the end of an asynchronous write to the stream.
Equals	Returns a boolean indicating if the value and this object instance are the same instance.
Flush	This has no purpose in a MemoryStream
GetHashCode	Returns a pseudo-unique number identifying this instance.
ReadBlock	Reads a specifiec number of bytes from the stream.
ReadByte	Reads a single byte from the stream.
SeekPosition	Sets the position within the current stream to the specified value.
SetLength	Sets the current length of the stream.
ToArray	Writes the stream contents to a byte array, regardless of the Position property.
ToString	Returns a string representation of this object instance.
WriteBlock	Writes an array of bytes to the underlying stream.
WriteByte	Writes a single byte to the underlying stream.
WriteTo	Writes the entire contents of this memory stream to another stream.

Remarks

The MemoryStream uses an array of bytes to back the data in memory. When the object is first created, no array is allocated until the first time the data must be accessed. The default capacity of the array is 4096 bytes. The capacity will grow by doubling the size of the current capacity. If The capacity needs to be larger, consider setting the Capacity directly to prevent the array from having to be resized as new data is written to the stream.

If the MemoryStream is created using a supplied Byte array, then no internal array will be allocated. The MemoryStream will access the supplied Byte array as if it were created by the MemoryStream object. As the underlying array is modified, the changes can be seen by directly accessing the array. Also, by modifying the array directly, the underlying stream will reflect the new data.

The Currency type is used for consistency across all stream objects. Internally, the MemoryStream only supports 2 ^ 31 bytes. Other streams may support more.

Caution

If a Byte array is being supplied to the MemoryStream and Mode is ShareMode, then the array must out-live the MemoryStream object. It is the responsibility of the user to destroy the array after the stream has been destroyed. The MemoryStream object maintains a reference to the same array in memory, but does not deallocate the array when finished. While the object is alive, the array is locked to prevent it from being ReDimed or Erased. Closing the stream will release the lock and reference to the array, at which point the user has full control of the array.

Examples

The following code example shows how to read and write data using memory as a backing store.

Public Sub Main()
    Dim FirstString()   As Byte
    Dim SecondString()  As Byte
    Dim ByteArray()     As Byte
    Dim CharArray()     As Integer
    Dim UniEncoding     As New UnicodeEncoding
    Dim MemStream       As New MemoryStream
    Dim Count As Long
    Dim i As Long
    
    FirstString = UniEncoding.GetBytes("Invalid file path characters are:")
    SecondString = UniEncoding.GetBytes(Path.GetInvalidPathChars)
    
    MemStream.WriteBlock FirstString, 0, CorArray.Length(FirstString)
    
    For i = LBound(SecondString) To UBound(SecondString)
        MemStream.WriteByte SecondString(i)
    Next
    
    Debug.Print CorString.Format(t("Capacity = {0}, Length = {1}, Position = {2}\n"), MemStream.Capacity, MemStream.Length, MemStream.Position)
    
    MemStream.SeekPosition 0, SeekOrigin.FromBeginning
    
    ReDim ByteArray(0 To MemStream.Length - 1)
    Count = MemStream.ReadBlock(ByteArray, 0, 20)
    
    Do While Count < MemStream.Length
        ByteArray(Count) = MemStream.ReadByte
        Count = Count + 1
    Loop
    
    ReDim CharArray(0 To UniEncoding.GetCharCount(ByteArray, 0, Count) - 1)
    UniEncoding.GetDecoder.GetChars ByteArray, 0, Count, CharArray, 0
    
    Debug.Print NewString(CharArray)
End Sub

' The example code produces the following output.
'
'    Capacity = 256, Length = 138, Position = 138
'
'    Invalid file path characters are:"<>| 

'    
'    

See Also

Project CorLib Overview

Class MemoryStream Overview

Constructors

Stream