Converting struct object to byte array

Hi,

I am needing to write data to a usb device. The USB device uses a byte array (DataArray() as byte) to store the data. How can I assign a struct object (myStruct(0)) to the byte array. I run into the error "Value of type byte cannot be converted to 1-dimensional array of byte" when I try to cast the struct as a byte.

You can use serialization to convert an object to binary data and vice versa. You would use a BinaryFormatter to write the object to a MemoryStream and then call GetBuffer to get the stream contents into a Byte array.

https://www.google.com.au/search?q=b...ient=firefox-a

alternatively, you can use the Marshal class:

vb Code:

Imports System.Runtime.InteropServices
 
Public Class Form1
 
    Private Structure s
        Dim a As Integer
        Dim b As String
        Dim c As Boolean
    End Structure
    Dim myStruct As New s With {.a = 1, .b = "one", .c = True}
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim Ptr As IntPtr = Marshal.AllocHGlobal(Marshal.SizeOf(myStruct))
        Dim ByteArray(Marshal.SizeOf(myStruct) - 1) As Byte
        'now copy structure to Ptr pointer 
        Marshal.StructureToPtr(myStruct, Ptr, False)
        'copy to byte array
        Marshal.Copy(Ptr, ByteArray, 0, Marshal.SizeOf(myStruct))
        Marshal.FreeHGlobal(Ptr)
 
    End Sub
 
End Class

.paul., are you aware of any potential pitfalls with either approach? I have to admit that I've never really had cause to use either so I'm not sure if one option has specific benefit over the other. I think that the code would be about the same length.

Thanks guys. If I use the marshal method, how can I read back the value from the byte array as a struct to confirm that it was sent correctly?

Quote:

---

Originally Posted by jmcilhinney

.paul., are you aware of any potential pitfalls with either approach? I have to admit that I've never really had cause to use either so I'm not sure if one option has specific benefit over the other. I think that the code would be about the same length.

---

not that i know of, but it does use unmanaged memory.
not sure how reliable that is...

Quote:

---

Originally Posted by mk48

Thanks guys. If I use the marshal method, how can I read back the value from the byte array as a struct to confirm that it was sent correctly?

---

vb Code:

Imports System.Runtime.InteropServices
 
Public Class Form1
 
    Private Structure s
        Dim a As Integer
        Dim b As String
        Dim c As Boolean
        Public Overloads Shared Operator =(ByVal s1 As s, ByVal s2 As s) As Boolean
            Return s1.a = s2.a AndAlso s1.b = s2.b AndAlso s1.c = s2.c
        End Operator
        Public Overloads Shared Operator <>(ByVal s1 As s, ByVal s2 As s) As Boolean
            Return s1.a <> s2.a OrElse s1.b <> s2.b OrElse s1.c <> s2.c
        End Operator
    End Structure
    Dim myStruct As New s With {.a = 1, .b = "one", .c = True}
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim Ptr As IntPtr = Marshal.AllocHGlobal(Marshal.SizeOf(myStruct))
        Dim ByteArray(Marshal.SizeOf(myStruct) - 1) As Byte
        'now copy structure to Ptr pointer 
        Marshal.StructureToPtr(myStruct, Ptr, False)
        'copy to byte array
        Marshal.Copy(Ptr, ByteArray, 0, Marshal.SizeOf(myStruct))
 
        Dim myStruct2 As New s
        myStruct2 = DirectCast(Marshal.PtrToStructure(Ptr, GetType(s)), s)
        MsgBox(myStruct = myStruct2)
 
        Marshal.FreeHGlobal(Ptr)
    End Sub
 
End Class

that last post should be:

vb Code:

Imports System.Runtime.InteropServices
 
Public Class Form1
 
    Private Structure s
        Dim a As Integer
        Dim b As String
        Dim c As Boolean
        Public Overloads Shared Operator =(ByVal s1 As s, ByVal s2 As s) As Boolean
            Return s1.a = s2.a AndAlso s1.b = s2.b AndAlso s1.c = s2.c
        End Operator
        Public Overloads Shared Operator <>(ByVal s1 As s, ByVal s2 As s) As Boolean
            Return s1.a <> s2.a OrElse s1.b <> s2.b OrElse s1.c <> s2.c
        End Operator
    End Structure
    Dim myStruct As New s With {.a = 1, .b = "one", .c = True}
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim Ptr As IntPtr = Marshal.AllocHGlobal(Marshal.SizeOf(myStruct))
        Dim ByteArray(Marshal.SizeOf(myStruct) - 1) As Byte
        'now copy structure to Ptr pointer 
        Marshal.StructureToPtr(myStruct, Ptr, False)
        'copy to byte array
        Marshal.Copy(Ptr, ByteArray, 0, Marshal.SizeOf(myStruct))
 
        Dim Ptr2 As IntPtr = Marshal.AllocHGlobal(ByteArray.Length)
        Marshal.Copy(ByteArray, 0, Ptr2, ByteArray.Length)
        Dim myStruct2 As New s
        myStruct2 = DirectCast(Marshal.PtrToStructure(Ptr2, GetType(s)), s)
 
        MsgBox(myStruct = myStruct2)
 
        Marshal.FreeHGlobal(Ptr)
    End Sub
 
End Class

Thanks! I knew something was off with the previous post considering you were using the same Ptr.

When I try this code:

Code:

---

TestStruct = DirectCast(Marshal.PtrToStructure(Ptr2, GetType(TestStruct)), teststruct)

---

I receive the error "Type TestStruct is not defined" although TestStruct is a structure object

I fixed it. I specified the struct object name instead of the struct type.