tracef(3)
=========
:object-type: macro


NAME
----
tracef - LTTng-UST printf(3)-like interface


SYNOPSIS
--------
[verse]
*#include <lttng/tracef.h>*

[verse]
#define *tracef*('fmt', ...)

Link with `-llttng-ust`.


DESCRIPTION
-----------
The LTTng-UST `tracef()` API allows you to trace your application with
the help of a simple man:printf(3)-like macro. The 'fmt' argument is
passed directly to the 'fmt' parameter of man:vasprintf(3), as well as
the optional parameters following 'fmt'.

To use `tracef()`, include `<lttng/tracef.h>` where you need it, and
link your application with `liblttng-ust`. See the <<example,EXAMPLE>>
section below for a complete usage example.

Once your application is instrumented with `tracef()` calls and
ready to run, use man:lttng-enable-event(1) to enable the
`lttng_ust_tracef:*` event.

The `tracef()` events contain a single field, named `msg`, which is the
formatted string output.

If you need to attach a specific log level to a `tracef()` call, use
man:tracelog(3) instead.

See also the <<limitations,LIMITATIONS>> section below for important
limitations to consider when using `tracef()`.


[[example]]
EXAMPLE
-------
Here's a usage example of `tracef()`:

-------------------------------------------------------------------
#include <stdlib.h>
#include <lttng/tracef.h>

int main(void)
{
    int i;

    for (i = 0; i < 25; i++) {
        tracef("my message: %s, this integer: %d", "a message", i);
    }

    return EXIT_SUCCESS;
}
-------------------------------------------------------------------

This C source file, saved as `app.c`, can be compiled into a program
like this:

[role="term"]
---------------------------
cc -o app app.c -llttng-ust
---------------------------

You can create an LTTng tracing session, enable the `tracef()` events,
and start the created tracing session like this:

[role="term"]
---------------------------------------------------
lttng create my-session
lttng enable-event --userspace 'lttng_ust_tracef:*'
lttng start
---------------------------------------------------

Next, start the program to be traced:

[role="term"]
-----
./app
-----

Finally, stop the tracing session, and inspect the recorded events:

[role="term"]
----------
lttng stop
lttng view
----------


[[limitations]]
LIMITATIONS
-----------
:macro-name: tracef

include::tracef-tracelog-limitations.txt[]


include::common-footer.txt[]

include::common-copyrights.txt[]

include::common-authors.txt[]


SEE ALSO
--------
man:tracelog(3),
man:lttng-ust(3),
man:lttng(1),
man:printf(3)