QCStringList and QCString complications...

[D. Michael McIntyre]

I picked a random target in the "Programme for Tedium" porting effort, and
zoomed in on QCString.  We seem to use this in a number of contexts where we
need to deal with data the old fashioned way, like writing a binary MIDI
file.  It has been replaced with QByteArray, and a compatibility class
Q3CString based on QByteArray:

 QCString

 In Qt 3, QCString inherited from QByteArray. The main drawback of this
 approach is that the user had the responsibility of ensuring that the string
 is '\0'-terminated. Another important issue was that conversions between
 QCString and QByteArray often gave confusing results....

 Qt 4 solves that problem by merging the QByteArray and QCString classes into
 one class called QByteArray. Most functions that were in QCString previously
 have been moved to QByteArray. The '\0' issue is handled by having QByteArray
 allocate one extra byte that it always sets to '\0'. For example:

   QByteArray ba("Hello");
   ba.size();             // returns 5 (the '\0' is not counted)
   ba.length();           // returns 5
   ba.data()[5];          // returns '\0'

 The Qt3Support library contains a class called Q3CString that inherits from
 the new QByteArray class and that extends it to provide an API that is as
 close to the old QCString class as possible. Note that the following
 functions aren't provided by Q3CString:

      * QCString::find(const QRegExp &, int)
      * QCString::findRev(const QRegExp &, int)
      * QCString::contains(const QRegExp &)
      * QCString::replace(const QRegExp &, const char *)

This description isn't so helpful for getting a quick idea of what we're
looking at, because it talks about what's missing from a compatibility class
we're going to try to avoid anyway, rather than talking directly and
obviously about how much of a 1:1 correspondence there is between the old QT3  
QCString and the new QT4 QByteArray.  We know "most functions" have been
merged, but without particle by particle investigation of each method of
QCString we use in what context, it's hard to get an overview of what we're
looking at.

I figured I'd try a simple swap, and maybe we'd get lucky and not use any
methods of the old QCString that don't have functionally identical
equivalents in the new QByteArray.  Without a lot of deep digging, it's hard
to evaluate how successful that effort was.

However, there is definitely a snag.  We also use QCStringList, which my swap
now converts to QByteArrayList.  Well, there's no QByteArrayList in QT4, so
my swap isn't quite robust enough to actually work anyway without more
refinement.  However, whats more troubling is the complete lack of
documentation anywhere about QCStringList.  I can guess what it's supposed to
do, but where are the damn API docs for it?

All I can find are uses of it in KDE code, with several of them seeming to be
related to DCOP code.  Google turns up nothing but code snippets in an
assortment of contexts.  No API anywhere.  Not even for QT2 or something.

Some of our QCStringLists look like they will have to be totally replaced with
something else anyway (as they relate to DCOP) but I don't think we're lucky
enough that all of them are going to disappear.  So we really need to build
some kind of equivalent, and without even knowing what the bloody hell that
even used to do, this is an irritating snag.

Well, anyway, on a positive note, I just busted my regex cherry and figured
out how to replace QCString but not QCStringList.  I'm definitely not enough
of a regex champ, nor am I aspiring to be one, to do a good job with most of
the really tricky nonsense like what Yves just spent five years on to
accomplish 1/10,000,000th of our job, but this should make me marginally less
useless for the porting effort.  Bully for me.  Huzzah.  I'm going to bed
now.

Porting is EVIL!

--
D. Michael McIntyre

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[cannam]

On Fri, Jul 18, 2008 at 6:00 AM, D. Michael McIntyre
<michael.mcintyre@...> wrote:
> I figured I'd try a simple swap, and maybe we'd get lucky and not use any
> methods of the old QCString that don't have functionally identical
> equivalents in the new QByteArray.

I think that has a good chance of working.  And I think anything it
misses will probably show up in compile errors rather than subtle
bugs.

> However, there is definitely a snag.  We also use QCStringList, which my swap
> now converts to QByteArrayList.  Well, there's no QByteArrayList in QT4, so
> my swap isn't quite robust enough to actually work anyway without more
> refinement.  However, whats more troubling is the complete lack of
> documentation anywhere about QCStringList.

A few greps later and I can tell you why -- it's just an opportunistic
typedef in the KDE headers.  Actually, it's so opportunistic that the
typedef appears several times in several different headers.
Fortunately, it's the same each time...

Anyway, it's

  typedef QValueList<QCString> QCStringList;

QValueList is just QList in Qt4-speak, so I think you should just be
able to directly replace QCStringList with QList<QByteArray>
throughout, and that will probably work.


Chris

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[D. Michael McIntyre]

On Friday 18 July 2008, you wrote:

> I think that has a good chance of working.  And I think anything it
> misses will probably show up in compile errors rather than subtle
> bugs.

I was worried in particular about one version automagically appends the /0
without increasing the return of size() and the other doesn't, so anything
requiring size() could be off by one.  Or something along those lines.  If we
even use that, and if there's actually any functional change in behavior.

> able to directly replace QCStringList with QList<QByteArray>

OK, done, and the conversion looks OK.  I also switched QValueList to
QLinkedList, as explained in the comment, though it looks like this only
occurs twice.  Once in DCOP stuff, and the other in printing-related stuff in
NotationView, both of which might be going away anyway.

Ten million and forty three to go.
--
D. Michael McIntyre

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