How-To: Logging

Step by Step Guide

Preparation

1. Import the logging library in your code:

   #include <kdblogger.h>

2. Insert logging statements:

   ELEKTRA_LOG("Hello, %s!", "🌎");

Log Everything

If Elektra should display all log messages, then please follow the steps below.

1. Uncomment the line:

   // #define NO_FILTER

   in the file src/libs/elektra/log.c.

2. Optional: Change the debug level in src/include/kdblogger.h. For example, if you want to see debug messages too, then change the line

   ELEKTRA_LOG_LEVEL = ELEKTRA_LOG_LEVEL_INFO,

   to

   ELEKTRA_LOG_LEVEL = ELEKTRA_LOG_LEVEL_DEBUG,

File Specific Logging

If you want to only log messages below a specific directory prefix, then please follow the steps below.

1. Search for the code:

   #ifndef NO_FILTER
        // XXX Filter level …
   #endif

   in the file src/libs/elektra/log.c.

2. Replace the code with something like:

   #ifndef NO_FILTER
        if (strncmp (file, "src/postfix/", sizeof ("src/postfix"))) goto end;
   #endif

   , where src/postfix contains all source files with logging statements that Elektra should log. For example, if you want to log everything from the yamlcpp plugin, then use the following code.

   #ifndef NO_FILTER
        if (strncmp (file, "src/plugins/yamlcpp/", sizeof ("src/plugins/yamlcpp"))) goto end;
   #endif

   . To log messages from multiple source you can use the operator && to chain multiple calls to strncmp. For example, to log messages from the directoryvalue and yamlcpp plugin use the code:

   #ifndef NO_FILTER
        if (strncmp (file, "src/plugins/directoryvalue/", sizeof ("src/plugins/directoryvalue")) &&
            strncmp (file, "src/plugins/yamlcpp/", sizeof ("src/plugins/yamlcpp")))
                goto end;
   #endif

Compilation

1. Enable the logger: e.g. run cmake with the switch -DENABLE_LOGGER=ON
2. Build Elektra

Log Levels

There are four log levels (ERROR is reserved for aborts within ELEKTRA_ASSERT):

• ELEKTRA_LOG_WARNING, something critical that should be shown to the user (e.g. API misuse), see ELEKTRA_LOG_LEVEL_WARNING
• ELEKTRA_LOG_NOTICE, something important developers are likely interested in, see ELEKTRA_LOG_LEVEL_NOTICE
• ELEKTRA_LOG, standard level gives information what the code is doing without flooding the log, see ELEKTRA_LOG_LEVEL_INFO
• ELEKTRA_LOG_DEBUG, for less important logs, see ELEKTRA_LOG_LEVEL_DEBUG