[#btck_witness_stack_get_item_at]
= btck_witness_stack_get_item_at
:mrdocs:

Serialize a witness stack item at a given index through the passed in callback.

== Synopsis

Declared in `<kernel/bitcoinkernel.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
[[nodiscard, __nonnull__]]
int
btck_witness_stack_get_item_at(
    xref:btck_WitnessStack-0e.adoc[btck_WitnessStack] const* witness_stack,
    size_t index,
    xref:btck_WriteBytes.adoc[btck_WriteBytes] writer,
    void* user_data);
----

== Return Value

The return value of the writer.

[NOTE]
====
The return value https://en.cppreference.com/cpp/language/attributes/nodiscard[should not be discarded^].
====
== Parameters

[cols="1,4"]
|===
| Name| Description
| *witness_stack* [in]
| Non‐null.
| *index* [in]
| Index of the item in the witness stack.
| *writer* [in]
| Non‐null, function pointer for writing bytes.
| *user_data* [in]
| Nullable, passed back through the writer callback.
|===

== Preconditions

* index < btck_witness_stack_count_items(witness_stack)


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