Writing a float value to unmanaged memory?

I'm building a .NET client and I referenced a RCW supplied by OPC 开发者_StackOverflow社区Foundation.

One of the functions has this parameter:

[IN] IntPtr pPercentDeadBand

The documentation mention that I should pass a pointer to a float value.

This is where I struggle. I found Marshall..WriteByte, .WriteInt16 and .Writeint32.

But nothing to write a float value from managed memory to unmanaged memory.

You can use Marshal.Copy instead and pass in a float[] with a single element.

Or you could stuff the bits from a float into an int and use Marshal.WriteInt32. This union-like struct can be used to convert between the two

[StructLayout(LayoutKind.Explicit)]
struct SingleInt32Union
{
    [FieldOffset(0)]
    float s;
    [FieldOffset(0)]
    int i;
}

I would do it in one of these ways, ordered from best to worst solution:

1. Change the Interop assembly definition of this method. If it is a pointer to a float it should be declared as follows.

   ref float pPercentDeadBand
   

   not

   [In] IntPtr pPercentDeadBand
   

2. Use unsafe code to pass a pointer to a float:

   unsafe
   {
       float theValueToPass = 345.26f;
       IntPtr thePointer = new IntPtr(&theValueToPass);
       //pass thePointer to the method;
   }
   

3. Allocate 4 bytes of memory using Marshal.AllocHGlobal, copy the float value from a single element float array using Marshal.Copy, call the method using the pointer received from Marshal.AllocHGlobal and then free the memory with Marshal.FreeHGlobal.

If it's the OPC Foundation, it appears as though they have a managed code API. UA SDK 1.00 includes support for .NET development environments, according to opcconnect.com.