[#EVP_MAC_update]
= EVP&lowbar;MAC&lowbar;update
:mrdocs:

Feed more message bytes into a MAC computation&period;

== Synopsis

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

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
int
EVP&lowbar;MAC&lowbar;update(
    xref:EVP_MAC_CTX.adoc[EVP&lowbar;MAC&lowbar;CTX]* ctx,
    unsigned char const* data,
    size&lowbar;t datalen);
----

== Return Value

1 on success, or 0 on failure&period;

== Parameters

[cols="1,4"]
|===
| Name| Description
| *ctx*
| MAC context previously initialised with EVP&lowbar;MAC&lowbar;init()&period;
| *data*
| Message bytes to absorb&period;
| *datalen*
| Number of bytes at `data&period;`
|===


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