[#BIO_callback_ctrl]
= BIO_callback_ctrl
:mrdocs:

Invoke a BIO ctrl that takes a BIO_info_cb callback pointer.

== Synopsis

Declared in `<openssl/bio.h>`

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

== Return Value

Command‐specific long result, or <=0 on error depending on `cmd.`

== Parameters

[cols="1,4"]
|===
| Name| Description
| *b*
| BIO to control.
| *cmd*
| Control command (for example BIO_CTRL_SET_CALLBACK).
| *fp*
| Callback function pointer passed as the ctrl argument.
|===


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