Calendar - Layout strings formatting.

In this simple example, we'll explain how to format the label displaying month and year, and also set weekday names.

To format month and year label, we need to create a callback function to create a string given the selected time, declared under a `struct tm` .

`struct tm` , declared on `time.h`, is a structure composed by nine integers:

- tm_sec seconds [0,59]
- tm_min minutes [0,59]
- tm_hour hour [0,23]
- tm_mday day of month [1,31]
- tm_mon month of year [0,11]
- tm_year years since 1900
- tm_wday day of week [0,6] (Sunday = 0)
- tm_yday day of year [0,365]
- tm_isdst daylight savings flag
  Note
    glib version has 2 additional fields.
  For our function, only stuff that matters are tm_mon and tm_year. But we don't need to access it directly, since there are nice functions to format date and time, as `strftime`. We will get abbreviated month (b) and year (y) (check strftime manpage for more) in our example:
  static char *
  _format_month_year(struct tm *format_time)
  {
  char buf[32];
  /* abbreviates month and year */
  if (!strftime(buf, sizeof(buf), "%b %y", format_time)) return NULL;
  return strdup(buf);
  }
  We need to alloc the string to be returned, and calendar widget will free it when it's not needed, what is done by `strdup`. So let's register our callback to calendar object:
  elm_calendar_format_function_set(cal, _format_month_year);
  To set weekday names, we should declare them as an array of strings:
  const char *weekdays[] =
  {
  "S", "M", "T", "W", "T", "F", "S"
  };
  And finally set them to calendar:
  elm_calendar_weekdays_names_set(cal, weekdays);
  Our example will look like this:

See the full source code calendar_example_02.c here.