[Qt-interest] Creating QPixmap from QByteArray causes segfault [SOLVED]

[Mandeep Sandhu]

On Wed, May 5, 2010 at 3:55 PM, Malyushytsky, Alex <alex at wai.com> wrote:
> To use QPixmap all you (should) need is an instance of QApplication -  QCoreApplication is not enough.

Correct. When I mentioned that my app worked, I was basically
including QApplication instead of QCoreApplication.

Initially I thought adding CONFIG += gui in the pro file would be
enough. But that wasn't the case.

Regards,
-mandeep

> This  may be only difference between gui - non-gui versions, if you don't need any gui for your  "tester" application and your system support gui in general..
>
> If you can't use QPixmap without showing some widget first, you are facing either bug in your code (likely) or in Qt (less likely).
>
> Regards,
>   Ale
>
>
> -----Original Message-----
> From: Mandeep Sandhu [mailto:mandeepsandhu.chd at gmail.com]
> Sent: Tuesday, May 04, 2010 10:52 PM
> To: Malyushytsky, Alex
> Cc: qt-interest at trolltech.com
> Subject: Re: [Qt-interest] Creating QPixmap from QByteArray causes segfault [SOLVED]
>
> On Wed, May 5, 2010 at 1:00 AM, Malyushytsky, Alex <alex at wai.com> wrote:
>>>> Is there a way I can instantiate QPixmap's in a non-GUI app?
>>
>> You can use QImage instead. It does not require GUI.
>
> I could. But I'm writing a helper/util class which will be used in a
> GUI app. So in the actual app there won;t be an issue, it's just that
> when I want to test it out...I don;t want to write a GUI app!!! :)
>
> Thanks,
> -mandeep
>
>>
>> Alex
>>
>> -----Original Message-----
>> From: qt-interest-bounces at trolltech.com [mailto:qt-interest-bounces at trolltech.com] On Behalf Of Mandeep Sandhu
>> Sent: Monday, May 03, 2010 9:56 PM
>> To: qt-interest at trolltech.com
>> Subject: Re: [Qt-interest] Creating QPixmap from QByteArray causes segfault [SOLVED]
>>
>> This error was coming because I was trying to use a QPixmap in a
>> console (non-GUI) application.
>>
>> It works fine if I use it in a GUI app.
>>
>> I'm actually writing a helper class, which was supposed to download an
>> image along with some other metatdata and emit this result.
>>
>> For testing this class I thought I'd make a simple console app and see
>> if it works. I did not want to go the GUI way since there really isn't
>> any GUI part to test.
>>
>> Is there a way I can instantiate QPixmap's in a non-GUI app?
>>
>> Thanks,
>> -mandeep
>>
>> On Mon, May 3, 2010 at 1:52 PM, Mandeep Sandhu
>> <mandeepsandhu.chd at gmail.com> wrote:
>>> Hi All,
>>>
>>> I'm trying to create a QPixmap from image data received from the
>>> network. I have connected the QNAM's finshed signal to my slot, which
>>> reads the data stream from the reply object (after all necessary error
>>> checks) and tries creating a QPixmap object using the loadFromData()
>>> API. However, this does not work and causes a seg fault! If I convert
>>> the byte array to a const char* then it doesn't seg fault but gives
>>> out the following error:
>>>
>>> Corrupt JPEG data: 1 extraneous bytes before marker 0xd9
>>> JPEG datastream contains no image
>>>
>>> The reply->bytesAvailable() shown in the finished signal exactly
>>> correspond to the number of bytes of the image. The image is not
>>> corrupt as I can see it eog/gqview/display progs w/o any error.
>>>
>>> Here's the snippet that converts the data to image:
>>>
>>> void getData(QNetworkReply* reply) {
>>>    qDebug() << "Status code"
>>>             <<
>>> reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt();
>>>
>>>    if (reply->error() != QNetworkReply::NoError) {
>>>        qDebug() << "Error fetching data from" << reply->url();
>>>        return;
>>>    }
>>>
>>>    qDebug() << "Bytes available" << reply->bytesAvailable();
>>>    if (reply->bytesAvailable() == 0) {
>>>        return;
>>>    }
>>>
>>>    QByteArray bytes = reply->readAll();
>>>    qDebug() << "Rx'ed" << bytes.size();
>>>
>>>    QPixmap pixi;
>>>    pixi.loadFromData(bytes.data());
>>>
>>>    reply->deleteLater();
>>> }
>>>
>>> I'm sure ppl have done this before and got it working.
>>>
>>> Any clues as to what could be going wrong?
>>>
>>> Thanks,
>>> -mandeep
>>>
>>
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