[#node-BlockManager-WriteBlockUndo]
= xref:node.adoc[node]::xref:node/BlockManager.adoc[BlockManager]::WriteBlockUndo
:relfileprefix: ../../
:mrdocs:

Write a block's undo data to disk and record it in the block index.

== Synopsis

Declared in `<node/blockstorage.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
[[requires_capability(0x7f2e1b0993d8), requires_capability(0x7f2e26d1ab38), requires_capability(0x7f2e375e0c18), requires_capability(0x7f2e33367fd8), requires_capability(0x7f2e3542efc8), requires_capability(0x7f2e28a73b28)]]
bool
WriteBlockUndo(
    xref:CBlockUndo.adoc[CBlockUndo] const& blockundo,
    xref:BlockValidationState.adoc[BlockValidationState]& state,
    xref:CBlockIndex.adoc[CBlockIndex]& block);
----

== Return Value

True on success, false if writing failed.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *blockundo*
| The undo data to store.
| *state*
| Validation state updated on failure.
| *block*
| The block index entry the undo data belongs to.
|===


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