[#OSSL_trace_set_callback]
= OSSL_trace_set_callback
:mrdocs:

Enable tracing for `category` by sending output to `callback.`

== Synopsis

Declared in `<openssl/trace.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
int
OSSL_trace_set_callback(
    int category,
    xref:OSSL_trace_cb.adoc[OSSL_trace_cb] callback,
    void* data);
----

== Description

Mutually exclusive with OSSL_trace_set_channel() for the same category.

== Return Value

1 on success, or 0 on failure.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *category*
| OSSL_TRACE_CATEGORY_* value selecting the channel.
| *callback*
| Trace callback, or NULL to disable tracing for `category.`
| *data*
| User pointer passed to `callback` on each invocation.
|===


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