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


NAME
----
lttng_ust_tracef, lttng_ust_vtracef - LTTng-UST printf(3)-like interface


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

[verse]
#define *lttng_ust_tracef*('fmt', ...)
#define *lttng_ust_vtracef*('fmt', 'ap')

Link with:

* `-llttng-ust`
* If you define `_LGPL_SOURCE` before including
  `<lttng/tracef.h>` (directly or indirectly): `-llttng-ust-common`


DESCRIPTION
-----------
The LTTng-UST `lttng_ust_tracef()` and `lttng_ust_vtracef()` API allows
you to trace your application with the help of simple man:printf(3)-like
and man:vprintf(3)-like macros.

The 'fmt' argument is passed directly as the 'fmt' parameter of
man:vasprintf(3), as well as:

For `lttng_ust_tracef()`::
    The optional parameters following 'fmt'.

For `lttng_ust_vtracef()`::
    The 'ap' parameter as the 'ap' parameter of man:vasprintf(3)
    (`va_list` type).

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

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

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

If you need to attach a specific log level to a
`lttng_ust_tracef()`/`lttng_ust_vtracef()` call, use
man:lttng_ust_tracelog(3) and man:lttng_ust_vtracelog(3) instead.

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


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

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

int main(void)
{
    int i;

    for (i = 0; i < 25; i++) {
        lttng_ust_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 -llttng-ust-common
----

You can create an LTTng tracing session, enable the `lttng_ust_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-suffix: tracef

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


include::common-footer.txt[]

include::common-copyrights.txt[]

include::common-authors.txt[]


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