At top left are the following lines:

slist: a singly linked list.

++ defined -- not defined

Below is a column of three three-tiered boxes, each with a number in the second tier: 1, 2, and 3, respectively. All three top tiers are blank, and the bottom tier of the bottom box is blank. Arrows point from the bottom tier of the “1” box down to the “2” box and from the bottom tier of the “2” box down to the “3” box. The tier with the “1” in the top box is labeled “begin()” and the space below the bottom box is labeled “end()”. A label at right reads “slist is not part of the STL and may not always be implemented. list is part of the STL”.

At top right are the following lines:

list: a doubly linked list.

Both ++ and -- defined

Below, the diagram is the same as the left diagram except arrows have been added from the top tier of the “2” box up to the “1” box and from the top tier of the “3” box up to the “2” box.