4.2.3 Maximum Height |

For efficiency, some of the BST routines use a stack of a fixed maximum
height. This maximum height affects the maximum number of nodes that
can be fully supported by libavl in any given tree, because a binary
tree of height *n* contains at most 2**n - 1 nodes.

The `BST_MAX_HEIGHT` macro sets the maximum height of a BST. The
default value of 32 allows for trees with up to 2**32 - 1 = 4,294,967,295 nodes. On today's common 32-bit computers
that support only 4 GB of memory at most, this is hardly a limit,
because memory would be exhausted long before the tree became too big.

The BST routines that use fixed stacks also detect stack overflow and call a routine to “balance” or restructure the tree in order to reduce its height to the permissible range. The limit on the BST height is therefore not a severe restriction.

28. <BST maximum height 28> = /* Maximum BST height. */ #ifndefBST_MAX_HEIGHT#defineBST_MAX_HEIGHT32 #endif

This code is included in 24, 142, 297, 415, and 519.

**Exercises:**

**1.** Suggest a reason why the `BST_MAX_HEIGHT` macro is defined
conditionally. Are there any potential pitfalls?
[answer]