QHashIterator doesn't work as expected (while QHash::const_iterator does)

[melon]

Hello everyone,

First: great forum, a lot of useful information. Thanks for all experienced users for support.

I have some issues while trying to iterate through QHash data structure designed as:

QHash<QString, QHash<QString, int> >

QHash<QString, QHash<QString, int> >

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A brief description of a class:

class RCDelayedRpcCaller : public QObject
{
    Q_OBJECT
public:
    explicit RCDelayedRpcCaller(renderclient::RenderClient *rc, QObject *parent = 0);
    (...)
private:
    //    el.name,       el.attr, value
    //       |               |      |
    QHash<QString, QHash<QString, int> > scalarHashTable; 
    (...)
//object that gets data from above data structure
    renderclient::RenderClient *renderClient; 
    (...)
};

class RCDelayedRpcCaller : public QObject
{
    Q_OBJECT
public:
    explicit RCDelayedRpcCaller(renderclient::RenderClient *rc, QObject *parent = 0);
    (...)
private:
    //    el.name,       el.attr, value
    //       |               |      |
    QHash<QString, QHash<QString, int> > scalarHashTable; 
    (...)
//object that gets data from above data structure
    renderclient::RenderClient *renderClient; 
    (...)
};

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When I'm trying to implement that with QHashIterator, the program crashes:

QHashIterator<QString, QHash<QString, int> > i(scalarHashTable);
    while (i.hasNext()){
	qDebug() << i.key();// crashes here; 
	QHash<QString, int> attribute = i.value();
	QHashIterator<QString, int> j(attribute);
	while (j.hasNext()){
	    renderClient->set_scalar_type_attribute(i.key(), j.key(), j.value());
	}
    }

QHashIterator<QString, QHash<QString, int> > i(scalarHashTable);
    while (i.hasNext()){
	qDebug() << i.key();// crashes here; 
	QHash<QString, int> attribute = i.value();
	QHashIterator<QString, int> j(attribute);
	while (j.hasNext()){
	    renderClient->set_scalar_type_attribute(i.key(), j.key(), j.value());
	}
    }

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In debuger it shows hashTable structures and it seems to be just fine. I've found that changing from iterator to following code works and does what's expected:

QHash<QString, QHash<QString, int> >::const_iterator i = scalarHashTable.constBegin();
	while (i != scalarHashTable.constEnd()){
	    QHash<QString, int>::const_iterator j = i.value().constBegin();
	    while (j != i.value().constEnd()){
		renderClient->set_scalar_type_attribute(i.key(), j.key(), j.value());
		++j;
	    }
	    ++i;
	}

QHash<QString, QHash<QString, int> >::const_iterator i = scalarHashTable.constBegin();
	while (i != scalarHashTable.constEnd()){
	    QHash<QString, int>::const_iterator j = i.value().constBegin();
	    while (j != i.value().constEnd()){
		renderClient->set_scalar_type_attribute(i.key(), j.key(), j.value());
		++j;
	    }
	    ++i;
	}

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What am I doing wrong? I'd like to use QHashIterator, as it looks better for my eyes but can't get it working.

[ChrisW67]

The value is not available until you call next() on the Java-style iterator:

QHashIterator<QString, QHash<QString, int> > i(scalarHashTable);
    while (i.hasNext()){
        (void) i.next();  // <<<<<< you have to step the Java-style iterator to get the value
	qDebug() << i.key();
	QHash<QString, int> attribute = i.value();
	QHashIterator<QString, int> j(attribute);
	while (j.hasNext()){
           (void) j.next();  // <<<<<< you have to step the Java-style iterator to get the value
 	    renderClient->set_scalar_type_attribute(i.key(), j.key(), j.value());
	}
    }

QHashIterator<QString, QHash<QString, int> > i(scalarHashTable);
    while (i.hasNext()){
        (void) i.next();  // <<<<<< you have to step the Java-style iterator to get the value
	qDebug() << i.key();
	QHash<QString, int> attribute = i.value();
	QHashIterator<QString, int> j(attribute);
	while (j.hasNext()){
           (void) j.next();  // <<<<<< you have to step the Java-style iterator to get the value
 	    renderClient->set_scalar_type_attribute(i.key(), j.key(), j.value());
	}
    }

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I am discarding the next() return value, you might want to capture it.

[melon]

Works as expected, thank you!

I assumed that hasNext() do the job, but that is just another "read the docs, Luke" case