win32utils devel - Nov 2004 - win32-file: nread and nwrite

Hi all,

I''ve got alpha versions of nread and nwrite now added to the win32-file
class in CVS.  They seem to work fine, although I''ve noticed one bug in
the File#read method.  Let''s say we have a text file with "hello
world"
in it.  If I call nread with no arguments, it works fine:

fh = File.nopen("C:\\test.txt")
p fh.nread -> "hello world"
fh.close

But, if I try to specify an argument, it seems to always want to return
9 to 11 bytes for some reason:

fh = File.nopen("C:\\test.txt")
p fh.nread(5) -> "hello\001u\002\003\000\002"
fh.close

How is it picking up these extra bytes?

Let''s modify test.txt to add the strings "this is a test" and
"1 2 3" on
their own lines.  Now, if we modify our code again to read, say, 15
bytes, it works fine:

fh = File.nopen("C:\\test.txt")
p fh.nread(15) -> "hello world\r\nth"
fh.close

So, that works as expected.  Why is it acting weird with strings under
12 bytes?

Dan

Hi,
> Hi all,
> 
> I''ve got alpha versions of nread and nwrite now added to the
win32-file
> class in CVS.  They seem to work fine, although I''ve noticed one
bug in
> the File#read method.  Let''s say we have a text file with
"hello world"
> in it.  If I call nread with no arguments, it works fine:
> 
> fh = File.nopen("C:\\test.txt")
> p fh.nread -> "hello world"
> fh.close
> 
> But, if I try to specify an argument, it seems to always want to return
> 9 to 11 bytes for some reason:
> 
> fh = File.nopen("C:\\test.txt")
> p fh.nread(5) -> "hello\001u\002\003\000\002"
> fh.close
> 
> How is it picking up these extra bytes?
> 
> Let''s modify test.txt to add the strings "this is a
test" and "1 2 3" on
> their own lines.  Now, if we modify our code again to read, say, 15
> bytes, it works fine:
> 
> fh = File.nopen("C:\\test.txt")
> p fh.nread(15) -> "hello world\r\nth"
> fh.close
> 
> So, that works as expected.  Why is it acting weird with strings under
> 12 bytes?
> 
> Dan
> 
That is due to a common pitfall of malloc :)

Insert
   memset(lpBuffer,0x00,dwBytesToRead+1);
after
   lpBuffer = (char*)malloc(dwBytesToRead+1);

Regards,

Park Heesob



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<snip>
> That is due to a common pitfall of malloc :)
> 
> Insert
>    memset(lpBuffer,0x00,dwBytesToRead+1);
> after
>    lpBuffer = (char*)malloc(dwBytesToRead+1);
> 
> Regards,
> 
> Park Heesob
Thanks.  Seems a strange thing to have to do.  I understand what memset
does, but I''m not entirely clear why I need it with malloc. 
I''ll read
up on it some more.

Dan