[#HMAC_Update]
= HMAC&lowbar;Update
:mrdocs:

Absorb more message bytes into an HMAC context (deprecated&semi; prefer EVP&lowbar;MAC&lowbar;update)&period;

== Synopsis

Declared in `&lt;openssl&sol;hmac&period;h&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
&lsqb;&lsqb;deprecated&rsqb;&rsqb;
int
HMAC&lowbar;Update(
    xref:HMAC_CTX.adoc[HMAC&lowbar;CTX]* ctx,
    unsigned char const* data,
    size&lowbar;t len);
----

[WARNING]
====
https://en.cppreference.com/cpp/language/attributes/deprecated[Deprecated^]. Use of this entity is allowed but discouraged.
====
== Return Value

1 on success, or 0 on failure&period;

== Parameters

[cols="1,4"]
|===
| Name| Description
| *ctx*
| HMAC context initialized with HMAC&lowbar;Init&lowbar;ex()&period;
| *data*
| Next chunk of message bytes&period;
| *len*
| Number of bytes at `data&period;`
|===


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