Re: [Vala] how can I get the number of unicode points in a string?

[琉璃井 <pharaoh456 163 com>]

发件人: 琉璃井 <pharaoh456 163 com>
发送时间: 2011-04-04 11:00
主 题: Re: [Vala] how can I get the number of unicode points in a string?
收件人:vala-list gnome org



于 2011/4/3 21:30, Adam Dingle 写道: 
 
>  On 04/03/2011 06:08 AM, 琉璃井 wrote: 
> >  From: "琉璃井"<pharaoh456 163 com> 
> >  Date: 2011-04-03 18:15:12 
> >  To: "Luca Bruno"<lethalman88 gmail com> 
> >  Subject: Re:Re: [Vala] how can I get the number of unicode points in 
> >  a string? 
> >
> >  At 2011-04-03 16:06:32，"Luca Bruno"<lethalman88 gmail com>  wrote: 
> >
> > >  On Sun, Apr 03, 2011 at 03:59:23PM +0800, 琉璃井 wrote: 
> > > >  I see that since 0.11.0 vala string.length returns number of bytes 
> > > >  rather than that of unicode characters, and string[i] returns only 
> > > >  one byte. I wonder how to deal with east Asian character strings. 
> > >  There are other methods in string that deal with utf8. For example 
> > >  char_count() and next_char(). 
> >  thank you. 
> >  I find char_count(), get_char() and next_char() in gtk+ document. 
> >  Looks like these methods are not covered in vala tutorial and document. 
> >  Is there something like string[i] for index access to utf8? I didn't 
> >  get it in docs. 
>
>  To get the i-th character, you could do this: 
>
>  str.get_char(str.index_of_nth_char(i)); 
>
>  But the current string methods are designed for iteration by offsets, 
>  not characters. So you should *not* do this, which will be inefficient: 
>
>  for (int i = 0 ; i<  str.char_count() ; ++i) // don't do this 
>  str.get_char(str.index_of_nth_char(i)); 
>
>  Instead, you want to iterate over the string using get_char() and 
>  next_char(). This is slightly inconvenient since these functions use 
>  pointers rather than integer offsets. In Vala trunk, Jürg has just 
>  committed a new method string.get_next_char() which will make it 
>  easier to iterate over strings: 
>
>  // in class string 
>  public bool get_next_char (ref int index, out unichar c); 
>
>  That isn't in any Vala release yet, though. (In the meantime, you 
>  might be able to copy and paste his implementation from glib-2.0.vapi 
>  in Vala trunk.) 
>
>  adam 
I know get_char and next_char are used for reducing iteration overhead, 
but there may be other convenient way to access a utf8 string with 
efficency. After all, getting a byte from a string using offset is not 
so resonable because people seldom needs to get a byte in a whole 
character. 
Is it possible to design the string like this: 
class string 
{ 
private unichar* buffer; 
private int* offset_array; 
... ... 
public unichar operator [](const int i) 
{ 
int offset=offset_array[i]; 
return buffer[offset]; 
} 
} 
offset_array stores the offset of utf8 charater by index. It is 
initialized in constructor or something. 
Then we can use string[index] with no iteration overhead.