Qt XmlQuery subquery attribute - c++

Question

I am trying to parse a gpx file using QXmlQuery (Qt 5.0).
The idea is to gather all the trkpt elements, and then subquery each element in order to extract latitude, longitude, altitude...
The problem is that it seems to not recognize the attribute name, because this code works:
query.setQuery
(
"declare default element namespace \"http://www.topografix.com/GPX/1/1\";"
"declare variable $gpxFile external;"
"doc($gpxFile)//trkpt"
);
if(query.isValid())
{
QXmlResultItems trkpts;
query.evaluateTo(&trkpts);
for(QXmlItem trkpt = trkpts.next(); !trkpt.isNull(); trkpt = trkpts.next())
{
QXmlQuery childQuery;
QStringList res;
childQuery.setFocus(trkpt);
childQuery.setQuery
(
"#*/string()"
); // <------------------------- this prints out all the attributes
childQuery.evaluateTo(&res);
qDebug() << res << "\n";
}
}
while this one does not:
// ... same code as above
childQuery.setQuery
(
"#lat/string()"
); // <------------------------- this prints out only a \n
// ... same code as above
any idea about what is wrong?
Please note that if I try to gather all the #lat attributes using the "outer" query, it works as expected:
query.setQuery
(
"declare default element namespace \"http://www.topografix.com/GPX/1/1\";"
"declare variable $gpxFile external;"
"doc($gpxFile)//trkpt/#lat/string()"
);
EDIT
This is a gpx sample file:
<?xml version="1.0" encoding="ISO-8859-1" standalone="yes"?>
<gpx
version="1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://www.topografix.com/GPX/1/0"
xmlns:topografix="http://www.topografix.com/GPX/Private/TopoGrafix/0/2"
xsi:schemaLocation="http://www.topografix.com/GPX/1/0 http://www.topografix.com/GPX/1/0/gpx.xsd http://www.topografix.com/GPX/Private/TopoGrafix/0/2 http://www.topografix.com/GPX/Private/TopoGrafix/0/2/topografix.xsd">
<trk>
<name>My track</name>
<desc>My track description</desc>
<trkseg>
<trkpt lat="38.919839863" lon="-121.020112049">
<ele>265.447754</ele>
<time>2003-02-05T18:19:20Z</time>
</trkpt>
<trkpt lat="38.919796947" lon="-121.020240795">
<ele>264.967041</ele>
<time>2003-02-05T18:19:20Z</time>
</trkpt>
<trkpt lat="38.919861320" lon="-121.020498287">
<ele>263.044434</ele>
<time>2003-02-05T18:19:20Z</time>
</trkpt>
<trkpt lat="38.919990066" lon="-121.020798694">
<ele>263.525146</ele>
<time>2003-02-05T18:19:20Z</time>
</trkpt>
</trkseg>
</trk>
</gpx>
EDIT
I found a workaround for this problem, by using QDomDocument instead of QXmlQuery.
The result looks like the code below (all error checks removed for sake of brevity):
QFile file = ("mytrack.gpx");
file.open(QIODevice::ReadOnly);
QDomDocument doc("mydoc");
doc.setContent(&file);
QDomElement root = doc.documentElement();
QDomNodeList trkpts = root.elementsByTagName("trkpt");
for(int i = 0; i < trkpts.length(); i++)
{
QDomElement e = trkpts.at(i).toElement();
QString latitude = e.attribute("lat");
QString longitude = e.attribute("lon");
QDomNodeList elevation_list = e.elementsByTagName("ele");
QString elevation = elevation_list.at(0).toElement().text();
// ... and so on
}
I would like to find a solution to this problem by using QXmlQuery, but in the meantime this just works.

Answer 1

I am not sure, because I don't know QXmlQuery and how it handles query parsing and execution. But I guess it could be a namespace issue. In the first query you define a default namespace, while in the second one you do not. Maybe this default namespace is not used in the second query (childQuery). At least it would fit to #*/String() printing something. Maybe you could try if #*:lat/string works as expected.
Otherwise, some example data would be very valuable.