[Interest] QFile::size() and QTextStream::pos()

[Thiago Macieira]

On Friday 30 October 2015 00:08:54 Elvis Stansvik wrote:
> > Slow? This is not the main problem. The main problem is that that seek()
> > and pos() uses device's units. But I need to seek() one character back,
> > and what then just -1, or -2, or something else? unget() can't be
> > implemented with methods of QTextStream.
> 
> Sorry if I'm missing something, but wouldn't you have that problem
> with std::istream::unget as well? It operates on chars (bytes).

istream operates on bytes, but QTextStream doesn't. QTextStream's internal 
buffer has already applied QTextCodec to convert from the raw binary format to 
Unicode (UTF-16). The number of codepoints you've read (# of QChars) and the 
number of bytes may not match at all.

If you wanted to do a codec conversion with istream, you'd do it on top, not 
below. Note that wistream classes (like wifstream) don't convert from 8-bit to 
wchar_t: they read wchar_t from the input. I don't know how to convert from 
(say) UTF-8 to UTF-16 or UCS-4 with istream, so you'd probably have to 
implement this by yourself and you might find the unget() functionality useful 
to unread incomplete multibyte sequences.

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center