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lni
20th September 2009, 06:38
Hi,

Is there an QVector replacement for explicit sharing?

Currently I am using QVector<float>, but it calls detach() when data() is called. If there a way not to call detach()? In another word, I need explicit sharing QVector.

Thanks

wysota
20th September 2009, 07:59
There is no such replacement. You can only pass references to the vector instead of copies of it everywhere.

lni
20th September 2009, 22:24
There is no such replacement. You can only pass references to the vector instead of copies of it everywhere.

I have to pass value of QVector<float>, at the same time I want to change value in one vector and all others get the same change.

Currently I do like this:

const float* data = vector.constData(); // <- doesn't call detach()
((float*)data)[ 3 ] = 5.6; // <- hard cast...

I know this is a very bad idea, but it is the only way not to call detach() and prevent copy on the write...

Any better idea?

scascio
21st September 2009, 09:50
Why not using shared pointers, from boost or some other lib?

lni
22nd September 2009, 03:26
I end up creating my own shared array using QVector



template <typename Type>
class QfwSharedArray
{
public:

QfwSharedArray() : d( new QfwSharedArrayData ) {
}

QfwSharedArray( const QVector<Type>& array ) : d( new QfwSharedArrayData ) {
setArray( array );
}

QfwSharedArray( const QfwSharedArray& org ) : d( org.d ) {
}

~QfwSharedArray() {
}

QfwSharedArray& operator=( const QfwSharedArray& rhs ) {
d = rhs.d;
return *this;
}

bool operator==( const QfwSharedArray& rhs ) const {
return d == rhs.d;
}

bool operator!=( const QfwSharedArray& rhs ) const {
return !operator==( rhs );
}

const QVector<Type>& array() const {
return d->array;
}
QVector<Type>& array() {
return d->array;
}

int size() const {
return d->array.size();
}

void resize( int size ) {
d->array.resize( size );
}

void setArray( const QVector<Type>& array ) {
d->array = array;
}

operator QVector<Type>&() {
return d->array;
}

operator const QVector<Type>&() const {
return d->array;
}

QVector<Type>& operator() () {
return d->array;
}

const QVector<Type>& operator() () const {
return d->array;
}

Type &operator[]( int i ) {
return d->array[ i ];
}

const Type &operator[]( int i ) const {
return d->array[ i ];
}

private:

class QfwSharedArrayData : public QSharedData {
public:
QVector<Type> array;
};

QExplicitlySharedDataPointer<QfwSharedArrayData> d;

};

template <typename Type>
QDebug operator<<( QDebug dbg, const QfwSharedArray<Type>& sa ) {
dbg.nospace() << sa.array();
return dbg.nospace();
}