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内存映射文件vbVerticalTab和vbNullChars将出现在结果中

memory-mapped-files vb.net

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bendecko · 技术社区 · 6 年前

我尝试使用内存映射文件(MMF)在应用程序之间存储和传输数据。

这是我的代码:

Public Class Form1
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        createMMF()
        readMMF()
    End Sub

    Sub createMMF()
        Dim mmf As MemoryMappedFile = MemoryMappedFile.CreateNew("testmap", 5)
        Dim stream As MemoryMappedViewStream = mmf.CreateViewStream()

        Dim writer As BinaryWriter = New BinaryWriter(stream)
        writer.Write("hello there")
    End Sub
    Sub readMMF()

        Dim mmf As MemoryMappedFile = MemoryMappedFile.OpenExisting("testmap")
        Dim stream As MemoryMappedViewStream = mmf.CreateViewStream()

        Dim streamReader = New StreamReader(stream)
        Dim text = streamReader.ReadToEnd()

        Debug.Print(text)

    End Sub

End Class

一些问题:

1) 在CreateNew调用中,我指定“5”作为大小,但是当我将.write调用从“hello”更改为“hello there”时,没有任何区别。

2) 当我在接收函数中读取流时,字符串就在那里,但是它在开始时包含了一个奇怪的字符(在调试器上下文中被解码为vbVerticalTab),随后还有大量的vbnullchar。

1 回复 | 直到 6 年前

1

bendecko 6 年前

好吧,多亏了你的评论,我才得以让这个工作起来。这是用于使用二进制编写器/读取器的代码。

   Sub createMMF()
        Dim mmf As MemoryMappedFile = MemoryMappedFile.CreateNew("testmap", 11)
        Dim stream As MemoryMappedViewStream = mmf.CreateViewStream()

        Dim writer As BinaryWriter = New BinaryWriter(stream)
        writer.Write("hello there")

    End Sub
    Sub readMMF()

        Dim mmf As MemoryMappedFile = MemoryMappedFile.OpenExisting("testmap")
        Dim stream As MemoryMappedViewStream = mmf.CreateViewStream()

        Dim binaryReader = New BinaryReader(stream)
        Dim length = binaryReader.Read()  'gives 11, length of "hello there" string.
        Dim text = binaryReader.ReadChars(length)

        Debug.Print(text)

    End Sub

另外,我使用StreamReader/Writer对进行了测试。我不得不在writer中使用一个.flush()调用,ReadToEnd方法仍然有很多空字符填充。

 Sub createMMF()
        Dim mmf As MemoryMappedFile = MemoryMappedFile.CreateNew("testmap", 11)
        Dim stream As MemoryMappedViewStream = mmf.CreateViewStream()

        Dim writer As StreamWriter = New StreamWriter(stream)
        writer.Write("hello there")
        writer.Flush()

    End Sub
    Sub readMMF()

        Dim mmf As MemoryMappedFile = MemoryMappedFile.OpenExisting("testmap")
        Dim stream As MemoryMappedViewStream = mmf.CreateViewStream()

        Dim streamReader = New StreamReader(stream)
        Dim text = streamReader.ReadToEnd()
        Debug.Print(text)

    End Sub

检查结果可以看到vbNull字符。