From kde-devel  Wed Aug 20 12:14:55 2003
From: Nicolas Goutte <nicolasg () snafu ! de>
Date: Wed, 20 Aug 2003 12:14:55 +0000
To: kde-devel
Subject: Re: QString data
X-MARC-Message: https://marc.info/?l=kde-devel&m=106138188510830

Just a question: are you sure that you cannot use QCString?

QCString would be indendant of UCS-2 or UCS-4, so you would not get this 
problem. (Of course the QCString would be probably in UTF-8 in this case.)

However, it does not avoid the deep copy of your data.

So personally, as you are already calling C functions for the mapping, I would 
go further and do the reading also with normal null-terminated C strings. 
Then you can compare with a QCString with Qt's portable functions like 
qstrcmp. (Of course, if your file cannot have null-terminated strings for a 
reason or another, my idea is not good.)

Have a nice day!

On Wednesday 20 August 2003 13:54, Johnny Andersson wrote:
> On Wednesday 20 August 2003 13.25, Tim Jansen wrote:
> > You can cast your string to const QChar* and use it as argument of
> > QConstString ( const QChar * unicode, uint length ), provided that:
> > - you are sure that all characters in your utf16 string have only 16 bits
> > (you may need to check that)
> > - you did not compile Qt with QT_QSTRING_UCS_4. In other words, QChar has
> > 2 bytes and not 4. You can check that at compile time, a sizeof(QChar)
> > should be enough
>
> Thanks for the replies (Tim and Harri). I'd really appreciate it if you
> could clear up a few points for me:
>
> I'm creating a program that converts a list of QStrings to a file that can
> be mmap()ed into memory (for later use on a handheld device). It's a
> dictionary application. What I want to do is to write strings to a file
> (using my Qt program), then mmap() the file and access the strings without
> copying them to RAM. What I'm doing now is:
>
> Write strings to file. I'm iteration through the strings, using
> QDataStream.writeRawBytes(string[i], sizeof(QChar)).
>
> Then I mmap() the file into the process, and I have a list of offsets to
> each string within the file. I create QConstString objects under the
> assumption that each character is sizeof(QChar).
>
> Would you say that's a good way to do it, or am I just lucky if it works?
> ;)
>
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