How can I pass a pointer to an array using p/invoke in C#?

Question

Example C API signature:

void Func(unsigned char* bytes);

In C, when I want to pass a pointer to an array, I can do:

unsigned char* bytes = new unsigned char[1000]; Func(bytes); // call 

How do I translate the above API to P/Invoke such that I can pass a pointer to C# byte array?

Answer 1

The easiest way to pass an array of bytes is to declare the parameter in your import statement as a byte array.

[DllImport EntryPoint="func" CharSet=CharSet.Auto, SetLastError=true] public extern static void Func(byte[]);  byte[] ar = new byte[1000]; Func(ar); 

You should also be able to declare the parameter as an IntPtr and Marshal the data manually.

[DllImport EntryPoint="func" CharSet=CharSet.Auto, SetLastError=true] public extern static void Func(IntPtr p);  byte[] ar = new byte[1000]; IntPtr p = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(byte)) * ar.Length); Marshal.Copy(ar, 0, p, ar.Length); Func(p); Marshal.FreeHGlobal(p);