contents/using-lttng/instrumenting/c-application/tracelog.md

   1 ---
   2 id: tracelog
   3 since: 2.7
   4 ---
   5
   6 The `tracelog()` API is very similar to [`tracef()`](#doc-tracef). The
   7 only difference is that it accepts an additional log level parameter.
   8
   9 The goal of `tracelog()` is to ease the migration from logging to
  10 tracing.
  11
  12 Here's an example:
  13
  14 ~~~ c
  15 #include <lttng/tracelog.h>
  16
  17 void my_function(int my_integer) {
  18     /* ... */
  19
  20     tracelog(TRACE_INFO, "my message, my integer: %d", my_integer);
  21
  22     /* ... */
  23 }
  24 ~~~
  25
  26 See [LTTng-UST library reference](#doc-liblttng-ust-tracepoint-loglevel)
  27 for the list of available log level names.
  28
  29 Link your application with `liblttng-ust`:
  30
  31 <pre class="term">
  32 gcc -o app app.c <strong>-llttng-ust</strong>
  33 </pre>
  34
  35 Execute the application as usual:
  36
  37 <pre class="term">
  38 ./app
  39 </pre>
  40
  41 The events produced by `tracelog()` calls are prefixed with
  42 `lttng_ust_tracelog:`. To enable `tracelog()` events matching a range
  43 of log levels, do:
  44
  45 <pre class="term">
  46 lttng enable-event --userspace 'lttng_ust_tracelog:*' \
  47                    --loglevel TRACE_INFO
  48 </pre>
  49
  50 This enables all `tracelog()` events with a log level at least as important
  51 as `TRACE_INFO`.
  52
  53 To enable `tracelog()` events matching a specific log level, do:
  54
  55 <pre class="term">
  56 lttng enable-event --userspace 'lttng_ust_tracelog:*' \
  57                    --loglevel-only TRACE_WARNING
  58 </pre>
  59
  60 See [Enabling and disabling events](#doc-enabling-disabling-events) for
  61 more options.