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Qt-interest Archive, August 2008
Strange bug with qWarning or QString.toAscii()

Message 1 in thread

Hello,

In the exec function of one dialog, I have the following :
[...]
QString noBug=noteEdit->toPlainText(); // get the textEdit content
qWarning("going to crash...");
qWarning(noBug.toAscii());
OTUtils::cleanString(noBug); // clean the string for an SQL statement
sql+="notes='"+noBug+"'";
[...]

As a test, I tried to paste a quite complicated string from a news paper on
the web
<http://www.lemonde.fr/economie/article/2008/08/27/edf-devrait-augmenter-ses-tarifs-pour-renover-son-reseau_1088279_3234.html>

and then it crashed at the qWarning(noBug.toAscii()); but only If I paste
the full text (Smaller part are OK).

The backtrace gives :
#5  0x080a1a91 in OTNewEventDlg::execAndProceed (this=0xbfa675f4) at
otneweventdlg.cpp:224
#4  0xb74cadc8 in qWarning () from /usr/lib/libQtCore.so.4
#3  0xb7517592 in qvsnprintf () from /usr/lib/libQtCore.so.4
#2  0xb7268c04 in vsnprintf () from /lib/tls/i686/cmov/libc.so.6
#1  0xb724788c in vfprintf () from /lib/tls/i686/cmov/libc.so.6
#0  0xb7278283 in strlen () from /lib/tls/i686/cmov/libc.so.6

Now, and this is what surprises me the most, to investigate the problem, I
created a slot to my dialog connected to the textChanged signal of the line
edit

void  OTNewEventDlg::testReact(){
  QString s= noteEdit->toPlainText();
  qWarning(s.toAscii());
}

but here,when I paste the text inside it doesn't crash ! Moreover, and in a
way this is what is important to me, if I remove all the qWarning in that
part of my code, everything is Ok, the sql statement constructed with the
dialog is executed without any glitche.

Is it that I am making a mistake so obvious that I can't see it or there a
strange bug here ?

Regards,

Alain

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Message 2 in thread

On Quarta 27 Agosto 2008 14:39:30 denebet wrote:
> qWarning(noBug.toAscii());

Are you sure that that string does not contain any printf-style replacements, 
like %s ?
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Message 3 in thread

Thiago Macieira wrote:

> On Quarta 27 Agosto 2008 14:39:30 denebet wrote:
>> qWarning(noBug.toAscii());
> 
> Are you sure that that string does not contain any printf-style
> replacements, like %s ?

As I wrote, I took the string in a newspaper article, it does have some "%"
inside and maybe after being pasted it becomes a printf-style
replacement.
I don't mind  very much if I can't use it on very complicated strings, but
I 'd prefer it to be explicitly written in the doc (well ,that may be
obvious for people used to printf but I am not).

Alain

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Message 4 in thread

On August 27, 2008 10:36:09 am denebet wrote:
> Thiago Macieira wrote:
> > On Quarta 27 Agosto 2008 14:39:30 denebet wrote:
> >> qWarning(noBug.toAscii());
> >
> > Are you sure that that string does not contain any printf-style
> > replacements, like %s ?
>
> As I wrote, I took the string in a newspaper article, it does have some "%"
> inside and maybe after being pasted it becomes a printf-style
> replacement.
> I don't mind  very much if I can't use it on very complicated strings, but
> I 'd prefer it to be explicitly written in the doc (well ,that may be
> obvious for people used to printf but I am not).
>
> Alain

Do this instead:
qWarning("%s", qPrintable(noBug));

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Message 5 in thread

Pascal Patry wrote:

>> Alain
> 
> Do this instead:
> qWarning("%s", qPrintable(noBug));
> 
OK, thanks.

Alain

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Message 6 in thread

denebet wrote:
>I don't mind  very much if I can't use it on very complicated strings,
> but I 'd prefer it to be explicitly written in the doc (well ,that may
> be obvious for people used to printf but I am not).

It is explicitly written in the documentation at
http://doc.trolltech.com/4.4/qtglobal.html#qWarning

Quoting from it:
"This function takes a format string and a list of arguments, similar to 
the C printf() function."

And it gives an example of formatting.

The documentation does not describe what the formatting is because that's 
explained much better in the C library documentation and in any C book.

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Message 7 in thread

Do you get a warning when you compile?  In Qt4, qWarning() expects a
const char*, but QString.toAscii() returns a QByteArray.

Try this instead:
qWarning(noBug.toAscii().data());

In Qt3 you could simply use QString.ascii(), but Trolltech did away with
that in Qt4.

Jason



-----Original Message-----
From: denebet [mailto:denebet@xxxxxxxxxxxx] 
Sent: Wednesday, August 27, 2008 5:40 AM
To: qt-interest@xxxxxxxxxxxxx
Subject: Strange bug with qWarning or QString.toAscii()

Hello,

In the exec function of one dialog, I have the following :
[...]
QString noBug=noteEdit->toPlainText(); // get the textEdit content
qWarning("going to crash...");
qWarning(noBug.toAscii());
OTUtils::cleanString(noBug); // clean the string for an SQL statement
sql+="notes='"+noBug+"'";
[...]

As a test, I tried to paste a quite complicated string from a news paper
on
the web
<http://www.lemonde.fr/economie/article/2008/08/27/edf-devrait-augmenter
-ses-tarifs-pour-renover-son-reseau_1088279_3234.html>

and then it crashed at the qWarning(noBug.toAscii()); but only If I
paste
the full text (Smaller part are OK).

The backtrace gives :
#5  0x080a1a91 in OTNewEventDlg::execAndProceed (this=0xbfa675f4) at
otneweventdlg.cpp:224
#4  0xb74cadc8 in qWarning () from /usr/lib/libQtCore.so.4
#3  0xb7517592 in qvsnprintf () from /usr/lib/libQtCore.so.4
#2  0xb7268c04 in vsnprintf () from /lib/tls/i686/cmov/libc.so.6
#1  0xb724788c in vfprintf () from /lib/tls/i686/cmov/libc.so.6
#0  0xb7278283 in strlen () from /lib/tls/i686/cmov/libc.so.6

Now, and this is what surprises me the most, to investigate the problem,
I
created a slot to my dialog connected to the textChanged signal of the
line
edit

void  OTNewEventDlg::testReact(){
  QString s= noteEdit->toPlainText();
  qWarning(s.toAscii());
}

but here,when I paste the text inside it doesn't crash ! Moreover, and
in a
way this is what is important to me, if I remove all the qWarning in
that
part of my code, everything is Ok, the sql statement constructed with
the
dialog is executed without any glitche.

Is it that I am making a mistake so obvious that I can't see it or there
a
strange bug here ?

Regards,

Alain

--
 [ signature omitted ]
Message 8 in thread

Use qPrintable:

qWarning("%s",qPrintable(noBug));

http://doc.trolltech.com/4.4/qtglobal.html#qPrintable

On Wed, Aug 27, 2008 at 8:37 PM, Jason Machacek <jmachacek@xxxxxxxxxxx> wrote:
> Do you get a warning when you compile?  In Qt4, qWarning() expects a
> const char*, but QString.toAscii() returns a QByteArray.
>
> Try this instead:
> qWarning(noBug.toAscii().data());
>
> In Qt3 you could simply use QString.ascii(), but Trolltech did away with
> that in Qt4.
>
> Jason
>
>
>
> -----Original Message-----
> From: denebet [mailto:denebet@xxxxxxxxxxxx]
> Sent: Wednesday, August 27, 2008 5:40 AM
> To: qt-interest@xxxxxxxxxxxxx
> Subject: Strange bug with qWarning or QString.toAscii()
>
> Hello,
>
> In the exec function of one dialog, I have the following :
> [...]
> QString noBug=noteEdit->toPlainText(); // get the textEdit content
> qWarning("going to crash...");
> qWarning(noBug.toAscii());
> OTUtils::cleanString(noBug); // clean the string for an SQL statement
> sql+="notes='"+noBug+"'";
> [...]
>
> As a test, I tried to paste a quite complicated string from a news paper
> on
> the web
> <http://www.lemonde.fr/economie/article/2008/08/27/edf-devrait-augmenter
> -ses-tarifs-pour-renover-son-reseau_1088279_3234.html>
>
> and then it crashed at the qWarning(noBug.toAscii()); but only If I
> paste
> the full text (Smaller part are OK).
>
> The backtrace gives :
> #5  0x080a1a91 in OTNewEventDlg::execAndProceed (this=0xbfa675f4) at
> otneweventdlg.cpp:224
> #4  0xb74cadc8 in qWarning () from /usr/lib/libQtCore.so.4
> #3  0xb7517592 in qvsnprintf () from /usr/lib/libQtCore.so.4
> #2  0xb7268c04 in vsnprintf () from /lib/tls/i686/cmov/libc.so.6
> #1  0xb724788c in vfprintf () from /lib/tls/i686/cmov/libc.so.6
> #0  0xb7278283 in strlen () from /lib/tls/i686/cmov/libc.so.6
>
> Now, and this is what surprises me the most, to investigate the problem,
> I
> created a slot to my dialog connected to the textChanged signal of the
> line
> edit
>
> void  OTNewEventDlg::testReact(){
>  QString s= noteEdit->toPlainText();
>  qWarning(s.toAscii());
> }
>
> but here,when I paste the text inside it doesn't crash ! Moreover, and
> in a
> way this is what is important to me, if I remove all the qWarning in
> that
> part of my code, everything is Ok, the sql statement constructed with
> the
> dialog is executed without any glitche.
>
> Is it that I am making a mistake so obvious that I can't see it or there
> a
> strange bug here ?
>
> Regards,
>
> Alain
>
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