How-To: Logging

Step by Step Guide

Preparation

1. Import the logging library in your code:

#include <kdblogger.h>

1. 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.

1. 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.

1. 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