From: Robert Feldt <feldt@...>
Date: 2000-12-28T21:22:50+09:00
Subject: [ruby-talk:8170] Speeding up string appends

Hi,

I need to convert large strings to valid C char arrays. A naive way goes
through the string while appending "#{str[i]}," to an output string but
this (of course) doesn't scale well. I tried:

# To speed up appends...
class AppendString
  def initialize(size)
    @str = " " * size
    @len = 0
  end
  def <<(astr)
    al = astr.length
    @str[@len, al] = astr
    @len += al
  end
  def to_s
    @str[0,@len]
  end
end

# Convert string to C-readable char array.
def string_to_c_char_array(str, arrayname = nil)
  s = AppendString.new(4*str.length) # Max 4 bytes per char
  s << "const char #{arrayname}[#{str.length}] = {" if arrayname
  for i in 0...(str.length-1)
    s << "#{str[i]},"
  end
  s << "#{str[str.length-1]}"
  s << "};" if arrayname
  s.to_s
end

but it still takes a long time (about 40 kB/s on my 366 Mhz laptop).

Is there a faster/better way?

Sorry if this has been discussed in any of the previous speed-up
threads; I haven't been following them.

Regards,

Robert