# Converting to UCS-2 or UTF-16 for use by a C extension

**URL:** <https://www.ruby-forum.com/t/converting-to-ucs-2-or-utf-16-for-use-by-a-c-extension/106262>\
**Category:** Ruby\
**Created:** [June 7, 2007, 10:06pm UTC](https://www.ruby-forum.com/t/converting-to-ucs-2-or-utf-16-for-use-by-a-c-extension/106262 "2007-06-07T22:06:33Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Wincent\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7993a0/32.png) [@Wincent\_C](https://www.ruby-forum.com/u/Wincent_C)\
**Post date:** [June 7, 2007, 10:06pm UTC](https://www.ruby-forum.com/t/converting-to-ucs-2-or-utf-16-for-use-by-a-c-extension/106262/1 "2007-06-07T22:06:33Z")

</div>

I’m working on a C extension that embeds an ANTLR parser, and I need  
to convert a Ruby input string into UCS-2 or possibly UTF-16 encoding.

I’ve got a working implementation but I suspect that it is flawed and  
just wanted to ask if this is the right way to do it. The basic idea  
is as follows (in pseudo-code):

// 1. unpack to array of UTF8 characters  
utf8 = input.unpack(“C\*”);

// 2. repack  
packed = utf8.pack(“U\*”);

// 3. convert using Iconv  
ucs2 = Iconv.iconv(“UCS-2”, “UTF-8”, packed).first

// 4. freeze  
ucs2.freeze

// 5. get pointer, and length (in 16 bit words)  
pointer = StringValuePtr(ucs2); // this bit in C  
count = ucs.length / 2;

// 6. hand off to the parser…

My doubts are basically as follows:

- I’m doing the unpack/repack because I am not sure that my string is  
encoded internally as UTF-8… it _seems_ to be, because if I type a  
string like “€” in irb then I can see that it’s composed of three  
bytes in UTF-8 ("\342\202\254")

- Is it in UTF-8 only because my system’s locale is set that way?  
might it be different on other people’s machines? (and if so, how  
would I find out what the encoding is?)

- In the case that the encoding is _not_ UTF-8, does my “round-trip”  
unpack/pack trick actually get it into UTF-8? (I don’t think it will!  
In which case the rount-trip is a waste of time)

- And once I’ve got the String in UCS-2, does StringValuePtr give me  
access to the raw UCS-2 encoded data like I think it does? (seems to)

- Does calling length on the UCS-2 encoded string always give the  
result in bytes? (I am almost certain that it does)

- Is there some more elegant way to get an arbitrary Ruby string into  
UCS-2 so that it can be handed off the C parser?

Cheers,  
Wincent