Initial data commit

Task/Singly-linked-list-Element-insertion/Delphi/singly-linked-list-element-insertion.delphi

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+// Using the same type defs from the one way list example.
+
+Type
+
+  // The pointer to the list structure
+  pOneWayList = ^OneWayList;
+
+  // The list structure
+  OneWayList = record
+                 pData : pointer ;
+                 Next  : pOneWayList ;
+               end;
+
+// I will illustrate a simple function that will return a pointer to the
+// new node or it will return NIL.  In this example I will always insert
+// right, to keep the code clear.  Since I am using a function all operations
+// for the new node will be conducted on the functions result.  This seems
+// somewhat counter intuitive, but it is the simplest way to accomplish this.
+
+Function InsertNode(VAR CurrentNode:pOneWayList): pOneWayList
+begin
+
+    // I try not to introduce different parts of the language, and keep each
+    // example to just the code required.  in this case it is important to use
+    // a try/except block.  In any OS that is multi-threaded and has many apps
+    // running at the same time, you cannot rely on a call to check memory available
+    // and then attempting to allocate.  In the time between the two, another
+    // program may have grabbed the memory you were trying to get.
+
+    Try
+      // Try to allocate enough memory for a variable the size of OneWayList
+      GetMem(Result,SizeOf(OneWayList));
+    Except
+      On EOutOfMemoryError do
+         begin
+           Result := NIL
+           exit;
+         end;
+    end;
+
+    // Initialize the variable.
+    Result.Next  := NIL ;
+    Reuslt.pdata := NIL ;
+
+    // Ok now we will insert to the right.
+
+    // Is the Next pointer of CurrentNode Nil?  If it is we are just tacking
+    // on to the end of the list.
+
+    if CurrentNode.Next = NIL then
+       CurrentNode.Next := Result
+    else
+      // We are inserting into the middle of this list
+      Begin
+         Result.Next      := CurrentNode.Next ;
+         CurrentNode.Next := result ;
+      end;
+end;