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

[Igor Mironchik]

On 30.10.2015 00:05, Thiago Macieira wrote:
> On Thursday 29 October 2015 21:49:40 Igor Mironchik wrote:
>> On 29.10.2015 06:51, Thiago Macieira wrote:
>>> On Thursday 29 October 2015 05:51:36 Igor Mironchik wrote:
>>>> P.S. Why QTextStream doesn't have something like get(), peek(), unget(),
>>>> putback()?
>>> Explain what you would want those functions to do.
>> The same like in std::istream, for example...
> The iostreams are, in my opinion, the worst part of the Standard Library. I
> don't consider them a good implementation, even if they have good ideas (<<
> and >>).
>
> istream			QTextStream
> get				read and readLine

Agree, read(), readLine(), and overloaded >> are completely cover get() 
usage.

> 	the overload with a delimiter: there was a discussion about replacing 	
> 	readLine with that, but it hasn't happened
> peek			<missing, no one has ever asked for it>

It can be useful in some cases, for example, when you implementing some 
sort of parsers where very often you need to know what next character is 
but don't really need to seek stream's position.

> unget			seek(pos() - 1) (slow! can't be avoided)

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.

> putback			<missing, really bad idea!>
>
> putback does the same as unget, plus adds a character that wasn't necessarily
> the last character that was read. Plus, the function has implementation-
> defined behaviour.

Agree. Without putback() I can live and be happy. And I really can't 
imagine why I need to putback() something different from that that was 
really read.


But peek() and unget() are very useful.

In my task I did parsing with just three functions like

skipWhiteSpace( QTextStream & stream, QList< QChar > & returned ),

skipComment( QTextStream & stream, QList< QChar > & returned ),

readWord( QTextStream & stream, QList< QChar > & returned )

where the main idea is that they read from "returned" if its not empty 
and only then from stream, and they can prepend() to the "returned" what 
equal to unget(). Such approach solved the problem with pos() and seek() 
and parsing effectiveness doesn't depends on buffer implementation of 
QTextStream...

-- 
Best Regards,
Igor Mironchik.