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

**URL:** <https://www.ruby-forum.com/t/re-shortcut-for-pack-p-unpack-l-first/94402>\
**Category:** Ruby\
**Created:** [May 3, 2006, 6:57pm UTC](https://www.ruby-forum.com/t/re-shortcut-for-pack-p-unpack-l-first/94402 "2006-05-03T18:57:55Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![BergerS\_Daniel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/bc8723/32.png) [@BergerS\_Daniel](https://www.ruby-forum.com/u/BergerS_Daniel)\
**Post date:** [May 3, 2006, 6:57pm UTC](https://www.ruby-forum.com/t/re-shortcut-for-pack-p-unpack-l-first/94402/1 "2006-05-03T18:57:55Z")

</div>

> > 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. 🙂

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.  
🙂

This communication is the property of Qwest and may contain confidential  
or  
privileged information. Unauthorized use of this communication is  
strictly  
prohibited and may be unlawful. If you have received this communication  
in error, please immediately notify the sender by reply e-mail and  
destroy  
all copies of the communication and any attachments.

---

<div class="post-metadata">

**Author:** ![BergerS\_Daniel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/bc8723/32.png) [@BergerS\_Daniel](https://www.ruby-forum.com/u/BergerS_Daniel)\
**Post date:** [May 3, 2006, 6:57pm UTC](https://www.ruby-forum.com/t/re-shortcut-for-pack-p-unpack-l-first/94402/2 "2006-05-03T18:57:57Z")

</div>

2006/5/1, Berger, Daniel [removed\_email\_address@domain.invalid](mailto: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. 🙂

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