[#BIO_set_callback]
= BIO_set_callback
:mrdocs:

Install a legacy pre/post I/O callback on a BIO (deprecated; prefer BIO_set_callback_ex).

== Synopsis

Declared in `<openssl/bio.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
[[deprecated]]
void
BIO_set_callback(
    xref:BIO.adoc[BIO]* b,
    xref:BIO_callback_fn.adoc[BIO_callback_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.
| *callback*
| Legacy callback function, or NULL to clear.
|===


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