Added support for strings in Struct type class

S7.Net/Types/S7StringAttribute.cs

@@ -0,0 +1,67 @@
+using System;
+
+namespace S7.Net.Types
+{
+    [AttributeUsage(AttributeTargets.Field, AllowMultiple = false)]
+    public sealed class S7StringAttribute : Attribute
+    {
+        private readonly S7StringType type;
+        private readonly int reservedLength;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="S7StringAttribute"/> class.
+        /// </summary>
+        /// <param name="type">The string type.</param>
+        /// <param name="reservedLength">Reserved length of the string in characters (default value is 254).</param>
+        /// <exception cref="ArgumentException">Please use a valid value for the string type</exception>
+        public S7StringAttribute(S7StringType type, int reservedLength = 254)
+        {
+            if (!Enum.IsDefined(typeof(S7StringType), type))
+                throw new ArgumentException("Please use a valid value for the string type");
+
+            this.type = type;
+            this.reservedLength = reservedLength;
+        }
+
+        /// <summary>
+        /// Gets the type of the string.
+        /// </summary>
+        /// <value>
+        /// The string type.
+        /// </value>
+        public S7StringType Type => type;
+
+        /// <summary>
+        /// Gets the reserved length of the string in characters.
+        /// </summary>
+        /// <value>
+        /// The reserved length of the string in characters.
+        /// </value>
+        public int ReservedLength => reservedLength;
+
+        /// <summary>
+        /// Gets the reserved length in bytes.
+        /// </summary>
+        /// <value>
+        /// The reserved length in bytes.
+        /// </value>
+        public int ReservedLengthInBytes => type == S7StringType.S7String ? reservedLength + 2 : (reservedLength * 2) + 4;
+    }
+
+
+    /// <summary>
+    /// String type.
+    /// </summary>
+    public enum S7StringType
+    {
+        /// <summary>
+        /// ASCII string.
+        /// </summary>
+        S7String,
+
+        /// <summary>
+        /// Unicode string.
+        /// </summary>
+        S7WString
+    }
+}