[#BIO_set_callback]
= BIO&lowbar;set&lowbar;callback
:mrdocs:

Install a legacy pre&sol;post I&sol;O callback on a BIO (deprecated&semi; prefer BIO&lowbar;set&lowbar;callback&lowbar;ex)&period;

== Synopsis

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

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
&lsqb;&lsqb;deprecated&rsqb;&rsqb;
void
BIO&lowbar;set&lowbar;callback(
    xref:BIO.adoc[BIO]* b,
    xref:BIO_callback_fn.adoc[BIO&lowbar;callback&lowbar;fn] callback);
----

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

[cols="1,4"]
|===
| Name| Description
| *b*
| BIO whose callback is replaced&period;
| *callback*
| Legacy callback function, or NULL to clear&period;
|===


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