VB.NET将字符串数组传递给C函数

Question

Wondering how to use VB.NET to call a C++ function with an array as a parameter:

dim mystring as string  = "a,b,c"
dim myarray() as string
myarray = split(mystring,",")
cfunction(myarray)

The cfuncton will be in C++, but I cannot use the string variable type in C++ due to other reasons, I can only use char. What should my C++ function look like in order to properly receive the array and split it back to its strings?

Answer 1

Basically, create some pinned memory to store the strings, and pass that to your function:

Marshal.AllocHGlobal will allocate some memory for you that you can give to your c++ function. See http://msdn.microsoft.com/en-us/library/s69bkh17.aspx . Your c++ function can accept that as a char * argument.

Example:

First, you'll need to convert your strings to one large byte[], separating each string with nulls (0x00). Let's do this efficiently by allocating just one byte array.

Dim strings() As String = New String() {"Hello", "World"}
Dim finalSize As Integer = 0
Dim i As Integer = 0
Do While (i < strings.Length)
    finalSize = (finalSize + System.Text.Encoding.ASCII.GetByteCount(strings(i)))
    finalSize = (finalSize + 1)
    i = (i + 1)
Loop
Dim allocation() As Byte = New Byte((finalSize) - 1) {}
Dim j As Integer = 0
Dim i As Integer = 0
Do While (i < strings.Length)
    j = (j + System.Text.Encoding.ASCII.GetBytes(strings(i), 0, strings(i).Length, allocation, j))
    allocation(j) = 0
    j = (j + 1)
    i = (i + 1)
Loop

Now, we just pass this to some memory we allocate using Marshal.AllocHGlobal

Dim pointer As IntPtr = Marshal.AllocHGlobal(finalSize)
Marshal.Copy(allocation, 0, pointer, allocation.Length)

Call your function here. You'll need to pass the number of strings you're giving the function too. Once you're done, remember to free the allocated memory:

Marshal.FreeHGlobal(pointer)

HTH.

(I don't know VB, but I do know C# and how to use Google ( http://www.carlosag.net/tools/codetranslator/ ), so sorry if it's a bit off! :P)

Answer 2

This example in C# it is the same as VB.NET, and it has the declaration of C++ method, if this what you want you can use it. C#: passing array of strings to a C++ DLL