[#BloombergLP-bslalg-BidirectionalLinkListUtil-isWellFormed]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bslalg.adoc[bslalg]::xref:BloombergLP/bslalg/BidirectionalLinkListUtil.adoc[BidirectionalLinkListUtil]::isWellFormed
:relfileprefix: ../../../
:mrdocs:

Return true if the bidirectional list starting from the specified `head`, and ending with the specified `tail` is well formed. A bidirectional list is well formed if `tail == head` (0 values are allowed) or all of the following conditions are met (note that `head` is renamed to `h` and `tail` to `t` for brevity):

== Synopsis

Declared in `<bslalg_bidirectionallinklistutil.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
static
bool
isWellFormed(
    xref:BloombergLP/bslalg/BidirectionalLink.adoc[BidirectionalLink]* head,
    xref:BloombergLP/bslalg/BidirectionalLink.adoc[BidirectionalLink]* tail);
----

== Description

1. `h` and `t` are valid addresses. 2. `h‐>nextLink()‐>previousLink() == h` is true. 3. `!h‐>previousLink() || h‐>previousLink()‐>nextLink() == h` is true. 4. `t‐>previousLink()‐>nextLink() == t` is true. 5. `!t‐>nextLink() || t‐>nextLink()‐>previousLink() == t` is true. 6. For each `link` in the list different than `h` and `t` both `link‐>nextLink()‐>previousLink() == link` and `link‐>previousLink()‐>nextLink() == link` are true.

The behavior is undefined unless `tail` can be reached from `head` following the chain of `nextLink` attributes of all the nodes in the open range `[head, tail)]`.


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