Chapter 8

sv_insert(sv, offset, length, "string to insert", strlen("string to insert"));

The next example shows how to remove characters from the start of a string:

SV *sv = newSVpv("Just another Perl hacker.", 0);

sv_chop(sv, SvPVX(sv) + 13);  // sv contains "Perl hacker" after this

The second parameter to sv_chop is a pointer into the string to the new first 

character.

If you need to do substring searches over a large string, you can speed up the 

process using the Boyer Moore search algorithm.

3

 This is done by first compiling 

the SV to be searched for with fbm_compile()

4

 and then searching with fbm_instr().

For example, here's a function that takes two SVs and returns the offset o f the 

second inside the first or  1 on failure. This function uses SvPVX and SvEND

5

 so it's 

only safe to call if both SVs are SvPOK() real code would include the necessary 

checks and conversions of course!

int fast_search (SV *source, SV *search) {

  char *found; // pointer to hold result of search

  // compile search string using Boyer Moore algorithm

  fbm_compile(search, 0);

  // conduct the search for the search string inside source

  found = fbm_instr(SvPVX(source), SvEND(source), search, 0);

  // if the search failed, return  1

  if (found == Nullch) return  1;

  // return the offset of search within source

  return found   SvPVX(source);

}

In my tests (looking for a single word in a string containing all of /usr/dict/words),

this version was between two and three times faster than a version that used Perl's 

index() function.

3. Boyer Moore is a search algorithm that matches without examining every character. It has 

the unusual feature of actually going faster the longer the match string is.

4. Note that fbm_compile() modifies the SV passed to it. As a result, it can't be used on constant 

SVs like those produced from string constants.

5. A macro that returns a pointer to the end of the string inside an SV

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