[#BIO_ctrl]
= BIO_ctrl
:mrdocs:

Invoke a type‐specific control operation on a BIO.

== Synopsis

Declared in `<openssl/bio.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
long
BIO_ctrl(
    xref:BIO.adoc[BIO]* bp,
    int cmd,
    long larg,
    void* parg);
----

== Return Value

Command‐specific long result; often 1 for success and 0/negative for failure.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *bp*
| BIO to control.
| *cmd*
| BIO_CTRL_* (or type‐specific) command code.
| *larg*
| Integer/long argument for `cmd.`
| *parg*
| Pointer argument for `cmd,` or NULL.
|===


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