Re: Shortcut for .pack("p*").unpack("l").first?


#1

If I want to get the underlying pointer address of a
Ruby string, I can do this:

What do you want with a memory address in Ruby-land? If
you’re in an extension then there’s probably an easier way to
get at the address.

Short answer: Win32API

strcmp1 = Win32API.new(‘msvcrt’, ‘strcmp’, ‘PP’, ‘I’)
strcmp2 = Win32API.new(‘msvcrt’, ‘strcmp’, ‘LL’, ‘I’)

str1 = “hello”
str2 = “hello”
str3 = “world”

addr1 = [str1].pack(“p*”).unpack(“l”).first
addr2 = [str2].pack(“p*”).unpack(“l”).first
addr3 = [str3].pack(“p*”).unpack(“l”).first

Using strings

strcmp1.call(str1, str2) # 0
strcmp1.call(str1, str3) # -1

Using string addresses

strcmp2.call(addr1, addr2) # 0
strcmp2.call(addr1, addr3) # -1

I suppose I could stop whining and just extend the String class. :slight_smile:

class String
def ptr
[self].pack(“p*”).unpack(“l”).first
end
end

This might be useful for Ruby/DL as well.

Regards,

Dan

PS - Many thanks to Heesob for teaching me some of these things lately.
:slight_smile:

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#2

2006/5/1, Berger, Daniel removed_email_address@domain.invalid:

What do you want with a memory address in Ruby-land? If
you’re in an extension then there’s probably an easier way to
get at the address.

Short answer: Win32API

Here you got me convinced.

Using strings

strcmp1.call(str1, str2) # 0
strcmp1.call(str1, str3) # -1

Using string addresses

strcmp2.call(addr1, addr2) # 0
strcmp2.call(addr1, addr3) # -1

Now you lost me again: if you can use a string as well as a pointer
then why bother to use the pointer? Are there places where you cannot
do that?

I suppose I could stop whining and just extend the String class. :slight_smile:

That’s definitively an option. :-))

class String
def ptr
[self].pack(“p*”).unpack(“l”).first
end
end

Just a thought: does it make sense to raise an exception or print a
warning if the string is not frozen? Otherwise the address could
point into limbo…

Cheers

robert