[#BIO_callback_ctrl]
= BIO&lowbar;callback&lowbar;ctrl
:mrdocs:

Invoke a BIO ctrl that takes a BIO&lowbar;info&lowbar;cb callback pointer&period;

== Synopsis

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

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
long
BIO&lowbar;callback&lowbar;ctrl(
    xref:BIO.adoc[BIO]* b,
    int cmd,
    xref:BIO_info_cb-08.adoc[BIO&lowbar;info&lowbar;cb]* fp);
----

== Return Value

Command&hyphen;specific long result, or &lt;&equals;0 on error depending on `cmd&period;`

== Parameters

[cols="1,4"]
|===
| Name| Description
| *b*
| BIO to control&period;
| *cmd*
| Control command (for example BIO&lowbar;CTRL&lowbar;SET&lowbar;CALLBACK)&period;
| *fp*
| Callback function pointer passed as the ctrl argument&period;
|===


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