This is derived from some C code I wrote to take a string (representing a set of characters) and return a string (also a set) of all the characters not found in that source string. (The NULL character is ignored.) 
char *complement (char *set) {
  int limit = 255;
  char *table = (char *) malloc((1+limit) * sizeof(char));  /* FIXED *
+/
  int i;

  /* populate table with all non-null characters */
  for (i = 0; i < limit; i++) table[i] = i+1;
  table[limit] = 0;

  /* for characters in 'set',
     make their value in the table NULL */
  while (*set) table[*set++ - 1] = 0;

  /* now, swap NULLs in the table with the last element
     in the table, to condense the table */
  for (i = 0; i < limit; i++)
    if (! table[i])
      table[i] = table[--limit], table[limit] = 0;

  return table;
}

[download]
So, the golf is, write this as Perl. The concept is basically, you have a string representing the characters in a character class, and you need to invert that class (ignoring the NULL character).

UPDATE: thanks to blokhead, I'm correcting my answer. I optimized and failed to test my optimization. My function body is 39 characters long. 
sub complement {
#        1         2         3
#23456789012345678901234567890123456789
join"",grep$_[0]!~/\Q$_/,map chr,1..255
#also
pack'C*',grep$_[0]!~/\Q@{[chr]}/,1..255
}

[download]

_____________________________________________________
Jeff[japhy]Pinyan: Perl, regex, and perl hacker, who'd like a job (NYC-area)
s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;

In reply to Golf: string complement by japhy

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