[Bug tapsets/20988] New: string tapset could use a strstr() type function

["dsmith at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=20988

            Bug ID: 20988
           Summary: string tapset could use a strstr() type function
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: tapsets
          Assignee: systemtap at sourceware dot org
          Reporter: dsmith at redhat dot com
  Target Milestone: ---

The string tapset has a function called 'instr()' that tells you if a substring
is present in a string, but the caller doesn't know where that substring is in
the string. It would be nice to have a tapset function that returns the index
of where a substring starts in a string. Then you could use the 'substr()'
tapset function to extract the string parts before and after a substring.

If the substring doesn't exist in string, the new tapset function should raise
an error.

Here's an example in action:

  # You've got a string that is in the general format 'FIRST.LAST'.
  # You want to break that string down into its parts.
  full = "David.Smith"

  # Find the index of the '.' character  
  index = NEW_FUNCTION(full, ".")

  # Extract the first part of the string
  first = substr(full, 0, index)

  # Extract the last part of the string
  last = substr(full, index + 1, strlen(full) - index - 1)

(I haven't checked all the indexing logic in the above example, but the idea is
there.)

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