From c5814672d54e1e2f720593d68d7c032158920e18 Mon Sep 17 00:00:00 2001
From: dahall <dahall@byu.net>
Date: Wed, 19 Aug 2020 20:51:11 -0600
Subject: [PATCH] Added protected size and offset values

---
 Core/InteropServices/SafeMemStruct.cs | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/Core/InteropServices/SafeMemStruct.cs b/Core/InteropServices/SafeMemStruct.cs
index 53565b71..b3c379db 100644
--- a/Core/InteropServices/SafeMemStruct.cs
+++ b/Core/InteropServices/SafeMemStruct.cs
@@ -17,14 +17,17 @@ namespace Vanara.InteropServices
 	/// <seealso cref="Vanara.InteropServices.SafeMemoryHandle{TMem}"/>
 	public abstract class SafeMemStruct<TStruct, TMem> : SafeMemoryHandle<TMem>, IEquatable<TStruct> where TMem : IMemoryMethods, new() where TStruct : struct
 	{
+		/// <summary>The structure size, in bytes, of TStruct.</summary>
+		protected static readonly SizeT BaseStructSize = InteropExtensions.SizeOf<TStruct>();
+
 		/// <summary>Initializes a new instance of the <see cref="SafeMemStruct{TStruct, TMem}"/> class.</summary>
 		/// <param name="s">The TStruct value.</param>
 		/// <param name="capacity">The capacity of the buffer, in bytes.</param>
-		protected SafeMemStruct(in TStruct s, SizeT capacity = default) : base(Math.Max((ulong)SizeOf<TStruct>(), (ulong)capacity)) => handle.Write(s);
+		protected SafeMemStruct(in TStruct s, SizeT capacity = default) : base(Math.Max(BaseStructSize, (ulong)capacity)) => handle.Write(s);
 
 		/// <summary>Initializes a new instance of the <see cref="SafeMemStruct{TStruct, TMem}"/> class.</summary>
 		/// <param name="capacity">The capacity of the buffer, in bytes.</param>
-		protected SafeMemStruct(SizeT capacity = default) : base(Math.Max((ulong)SizeOf<TStruct>(), (ulong)capacity)) { }
+		protected SafeMemStruct(SizeT capacity = default) : base(Math.Max(BaseStructSize, (ulong)capacity)) { }
 
 		/// <summary>Initializes a new instance of the <see cref="SafeMemStruct{TStruct, TMem}"/> class.</summary>
 		/// <param name="ptr">The PTR.</param>
@@ -116,7 +119,10 @@ namespace Vanara.InteropServices
 		/// <returns>A <see cref="System.String"/> value held by this instance or <c>null</c> if the handle is invalid.</returns>
 		public override string ToString() => ((TStruct?)this).ToString();
 
-		private static SizeT SizeOf<T>() => InteropExtensions.SizeOf<T>();
+		/// <summary>Returns the field offset of the named field.</summary>
+		/// <param name="name">The field name.</param>
+		/// <returns>The offset, in bytes, of the field within the structure.</returns>
+		protected static long FieldOffset(string name) => Marshal.OffsetOf(typeof(TStruct), name).ToInt64();
 
 #if ALLOWSPAN
 		/// <summary>Gets a reference to a structure based on this allocated memory.</summary>