[#BIO_set_callback_ex]
= BIO_set_callback_ex
:mrdocs:

Install an extended pre/post I/O callback on a BIO.

== Synopsis

Declared in `<openssl/bio.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
void
BIO_set_callback_ex(
    xref:BIO.adoc[BIO]* b,
    xref:BIO_callback_fn_ex.adoc[BIO_callback_fn_ex] callback);
----

== Parameters

[cols="1,4"]
|===
| Name| Description
| *b*
| BIO whose callback is replaced.
| *callback*
| Extended callback function, or NULL to clear.
|===


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