[#BIO_get_callback_arg]
= BIO&lowbar;get&lowbar;callback&lowbar;arg
:mrdocs:

Return the opaque callback&hyphen;argument pointer stored on a BIO&period;

== Synopsis

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

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
char*
BIO&lowbar;get&lowbar;callback&lowbar;arg(xref:BIO.adoc[BIO] const* b);
----

== Return Value

Pointer previously passed to BIO&lowbar;set&lowbar;callback&lowbar;arg(), or NULL&period;

== Parameters

[cols="1,4"]
|===
| Name| Description
| *b*
| BIO to query&period;
|===


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