# String segfault with wide character function, Windows

**URL:** <https://www.ruby-forum.com/t/string-segfault-with-wide-character-function-windows/61822>\
**Category:** Ruby\
**Created:** [May 28, 2006, 7:07am UTC](https://www.ruby-forum.com/t/string-segfault-with-wide-character-function-windows/61822 "2006-05-28T07:07:51Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\
**Post date:** [May 28, 2006, 7:07am UTC](https://www.ruby-forum.com/t/string-segfault-with-wide-character-function-windows/61822/1 "2006-05-28T07:07:51Z")

</div>

Ruby 1.8.4 (one click)  
Windows XP

Check this out segfault:

# strtest.rb

require ‘Win32API’

GetFullPathNameW = Win32API.new(‘kernel32’,‘GetFullPathNameW’,‘PLPP’,  
‘L’)

path = “C:\test”  
buf = 0.chr \* 260

if GetFullPathNameW.call(path, buf.size, buf, 0) == 0  
puts “Failed”  
end

#p buf  
p buf.split("\0\0").first # boom!

# Result

strtest.rb:13: [BUG] Segmentation fault  
ruby 1.8.4 (2005-12-24) [i386-mswin32]

This application has requested the Runtime to terminate it in an unusual  
way. Please contact the application’s support team for more information.

I noticed that if I dropped the ‘buf’ to 245 or fewer characters, it  
works ok. Also, it segfaults on just about any op that modifies buf,  
not just String#split.

Any ideas?

Thanks,

Dan

---

<div class="post-metadata">

**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\
**Post date:** [May 29, 2006, 5:14am UTC](https://www.ruby-forum.com/t/string-segfault-with-wide-character-function-windows/61822/2 "2006-05-29T05:14:22Z")

</div>

Daniel B. wrote:

> path = “C:\test”  
> strtest.rb:13: [BUG] Segmentation fault
> 
> Thanks,
> 
> Dan

The solution was found by Heesob, which I have pasted below (taken from  
the win32utils-devel mailing list):

I have found out what is the problem.  
It’s not bug of Ruby or Windows, it is only bug of code.

First try this:

require ‘Win32API’  
GetFullPathNameW = Win32API.new(‘kernel32’,‘GetFullPathNameW’,‘PLPP’,  
‘L’)  
for i in 1…100  
path = “c:\test”  
buf = 0.chr \* 260  
if GetFullPathNameW.call(path, buf.size, buf, 0) == 0  
puts “Failed”  
end  
p buf.split("\0\0").first  
end

It will cause various errors like  
uninitialized constant GetFullPathNameW (NameError)  
or  
segfault.

Next, try this:

require ‘Win32API’  
GetFullPathNameW = Win32API.new(‘kernel32’,‘GetFullPathNameW’,‘PLPP’,  
‘L’)  
for i in 1…100  
path = “c:\test”  
buf = 0.chr \* 260

# buf.size/2 -\> actual length of buf

if GetFullPathNameW.call(path, buf.size/2, buf, 0) == 0  
puts “Failed”  
end  
p buf.split("\0\0").first  
end

It runs Ok. but the result is not correct.

Next , try this:

require ‘Win32API’  
GetFullPathNameW = Win32API.new(‘kernel32’,‘GetFullPathNameW’,‘PLPP’,  
‘L’)  
for i in 1…100

# append \0 to path

path = “c:\test\0”  
buf = 0.chr \* 260

# buf.size/2 -\> actual length of buf in unicode string

if GetFullPathNameW.call(path, buf.size/2, buf, 0) == 0  
puts “Failed”  
end  
p buf.split("\0\0").first  
end

It runs ok. The result is correct.

Finally, the complete and correct code is like this:

require ‘Win32API’  
GetFullPathNameW = Win32API.new(‘kernel32’,‘GetFullPathNameW’,‘PLPP’,  
‘L’)  
for i in 1…100  
path = “c\0:\0\\0t\0e\0s\0t\0\0”  
buf = 0.chr \* 260

# buf.size/2 -\> actual length of buf in unicode string

if GetFullPathNameW.call(path, buf.size/2, buf, 0) == 0  
puts “Failed”  
end  
buf = buf.split("\0\0").first  
buf = (buf.size % 2).zero? ? buf : buf+"\0"  
p buf  
end

Remeber, Ruby’s string is terminated with “\0” implicitly, but UTF16  
string requires double “\0”.  
For ascii chars, it happens trailing three “\0” : one for ascii char  
and two for string termination.

Regards,

Park H.