Qt-interest Archive, July 2007
Forcing a QString deep copy without changing the data
Message 1 in thread
Version: QT4
QByteArray and QString have a fromRawData. The pointer to the data
is not interpreted so it is a nice way of loading raw bytes into the
string. The docs say that the QString/ByteArray will do a deep copy
of the data if there is a change. I want to force that deep copy
without changing the contents.
So you might ask why. I am reading a series of bytes. The first one
or two bytes, depending on those bytes, indicate Unicode or Ascii
strings. I read the raw data into a QByteArray. If I discover that
the data actually represents Unicode, I can do this. QString
aString; aString.fromRawData(aByteArray.data(), aByteArray.size());
The problem is that the data pointer returned by aByteArray is owned
by aByteArray. How do I force the deep copy?
Best practice?
Michael
--
[ signature omitted ]
Message 2 in thread
On Wednesday 04 July 2007 04:35:55 Michael Simpson wrote:
> Version: QT4
>
> QByteArray and QString have a fromRawData. The pointer to the data
> is not interpreted so it is a nice way of loading raw bytes into the
> string. The docs say that the QString/ByteArray will do a deep copy
> of the data if there is a change. I want to force that deep copy
> without changing the contents.
>
> So you might ask why. I am reading a series of bytes. The first one
> or two bytes, depending on those bytes, indicate Unicode or Ascii
> strings. I read the raw data into a QByteArray. If I discover that
> the data actually represents Unicode, I can do this. QString
> aString; aString.fromRawData(aByteArray.data(), aByteArray.size());
> The problem is that the data pointer returned by aByteArray is owned
> by aByteArray. How do I force the deep copy?
>
> Best practice?
I would do something like this:
QString aString;
aString = QString::fromRawData(aByteArray.constData(), aByteArray.size());
...
// force a deep copy
aString = QString::fromUtf16(aString.utf16());
--
[ signature omitted ]
Message 3 in thread
PERFECT! And thank you!
M
On Jul 3, 2007, at 10:11 PM, Bradley T Hughes wrote:
> On Wednesday 04 July 2007 04:35:55 Michael Simpson wrote:
>> Version: QT4
>>
>> QByteArray and QString have a fromRawData. The pointer to the data
>> is not interpreted so it is a nice way of loading raw bytes into the
>> string. The docs say that the QString/ByteArray will do a deep copy
>> of the data if there is a change. I want to force that deep copy
>> without changing the contents.
>>
>> So you might ask why. I am reading a series of bytes. The first one
>> or two bytes, depending on those bytes, indicate Unicode or Ascii
>> strings. I read the raw data into a QByteArray. If I discover that
>> the data actually represents Unicode, I can do this. QString
>> aString; aString.fromRawData(aByteArray.data(), aByteArray.size());
>> The problem is that the data pointer returned by aByteArray is owned
>> by aByteArray. How do I force the deep copy?
>>
>> Best practice?
>
> I would do something like this:
>
> QString aString;
> aString = QString::fromRawData(aByteArray.constData(),
> aByteArray.size());
>
> ...
>
> // force a deep copy
> aString = QString::fromUtf16(aString.utf16());
>
> --
> Bradley T. Hughes - bhughes at trolltech.com
> Trolltech ASA - Sandakervn. 116, P.O. Box 4332 Nydalen, 0402 Oslo,
> Norway
--
[ signature omitted ]
Message 4 in thread
On 7/4/07, Michael Simpson <michaelsimpson@xxxxxxx> wrote:
>
> Version: QT4
>
> QByteArray and QString have a fromRawData. The pointer to the data
> is not interpreted so it is a nice way of loading raw bytes into the
> string. The docs say that the QString/ByteArray will do a deep copy
> of the data if there is a change. I want to force that deep copy
> without changing the contents.
>
AFAIK, calling any non-const method, will cause a deep copy. Kinda dirty
trick, but should work fine.
You could create several overloads for different implicitly shared classed
like:
QString detach(const QString& str) {
QString detached(str);
detached.data();
return detached;
}
then, you can use it like this:
foo(detach(someOtherStr)); //foo receives a uniq string (hopefully)
--
[ signature omitted ]
Message 5 in thread
I like it but is the a risk that Trolltech could change this
implementation and break it later? I'll have to look at the code.
Thanks,
M
On Jul 4, 2007, at 8:05 AM, Pavel Antokolsky aka Zigmar wrote:
> On 7/4/07, Michael Simpson <michaelsimpson@xxxxxxx> wrote:
> Version: QT4
>
> QByteArray and QString have a fromRawData. The pointer to the data
> is not interpreted so it is a nice way of loading raw bytes into the
> string. The docs say that the QString/ByteArray will do a deep copy
> of the data if there is a change. I want to force that deep copy
> without changing the contents.
> AFAIK, calling any non-const method, will cause a deep copy. Kinda
> dirty trick, but should work fine.
>
> You could create several overloads for different implicitly shared
> classed like:
> QString detach(const QString& str) {
> QString detached(str);
> detached.data();
> return detached;
> }
>
> then, you can use it like this:
> foo(detach(someOtherStr)); //foo receives a uniq string (hopefully)
>
> --
> Best regards,
> Zigmar
