How to find the nth occurence of a string

[Tony Balinski]

Quoting Eric Bouyoux <eric.bouyoux at insidefr.com>:

> Hi,
>
> Has anybody already written a macro that help to find the nth occurence
> ofa string ?
You can almost do it with a regex: given N as a decimal, searching for
  (?:(?n.*?)(?:SearchString)){N}
will select from where you are upto the end of the Nth occurrence of
SearchString.

So a macro could be written looking like this:
=========================================================================
    title = "Search for Nth"
    re = string_dialog(title "\nEnter RE to find")
    if (re == "")
      return dialog(title "\nNo RE to find")

    n = string_dialog(title "\nFind which occurrence of '" re "'?", \
                      "From start", "From cursor")
    if (!valid_number(n) || n < 1)
      return dialog(title "\nNo RE occurrence number to find")

    if ($string_dialog_button == 1)
      pos = 0
    else
      pos = $cursor

    ok = 1
    if (n > 1) # find end of (n-1)th occurrence
      {
      --n
      full_re = "(?:(?n.*?)(?:" re ")){" n "}"
            res = search(full_re, pos, "regex")
      ok = (res >= 0)
      pos = $search_end
      }
    if (ok) # find final occurrence
      {
      res = search(re, pos, "regex")
      ok = (res >= 0)
      }

    if (!ok)
      return dialog(title "\nThe following RE was not found " \
                    (n + 1) " times:\n  " re)

    select(res, $search_end)
    set_cursor_pos($search_end)
=========================================================================