Parsing nested xml with boost - c++

Question

I have an xml which I like to read into my program, I've seen a lot of exmaples how to read xml using property tree from boost, however I couldn't make it work for the nested xml that I have:
<?xml version="1.0" encoding="UTF-8"?>
<document version="1.3.0">
<chunk>
<sensors>
<sensor id="0" label="unknown" type="frame">
<resolution width="2056" height="2464"/>
<property name="fixed" value="0"/>
<calibration type="frame" class="adjusted">
<resolution width="2056" height="2464"/>
<fx>7349.85579147491</fx>
<fy>7349.85579147491</fy>
<cx>1028</cx>
<cy>1232</cy>
<p1>0.000308132854297239</p1>
<p2>-0.000521332855614243</p2>
</calibration>
</sensor>
</sensors>
<cameras>
<camera id="0" label="img0000.png" sensor_id="0" enabled="1">
<transform>1.0000000000000000e+000 0.0000000000000000e+000 0.0000000000000000e+000 0.0000000000000000e+000 0.0000000000000000e+000 -1.0000000000000000e+000 -1.2246467991473532e-016 0.0000000000000000e+000 0.0000000000000000e+000 1.2246467991473532e-016 -1.0000000000000000e+000 0.0000000000000000e+000 0.0000000000000000e+000 0.0000000000000000e+000 0.0000000000000000e+000 1.0000000000000000e+000</transform>
</camera>
<camera id="1" label="img0011.png" sensor_id="0" enabled="1">
<transform>9.8183676675341047e-001 -2.7892274662900951e-002 -1.8766615162393202e-001 1.3502780959894856e+000 -2.8076662610258110e-002 -9.9960436765543659e-001 1.6760611099915072e-003 -8.8020303958543274e-003 -1.8763865398120155e-001 3.6234208013954891e-003 -9.8223144235654503e-001 -1.1015316085201440e-001 0.0000000000000000e+000 0.0000000000000000e+000 0.0000000000000000e+000 1.0000000000000000e+000</transform>
</camera>
</cameras>
<reference>LOCAL_CS["Local Coordinates (m)",LOCAL_DATUM["Local Datum",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]]]</reference>
<region>
<center>-5.1216167685514069e-002 -7.0600760442627708e-001 -6.9904047240845895e+000</center>
<size>2.1074647950629393e+000 1.5533586459855240e+000 1.0253878730038792e+000</size>
<R>-9.6011547075389880e-001 2.7340714563038887e-001 5.8539008680217816e-002 -2.6221584379471408e-001 -9.5313222127937347e-001 1.5093647677772853e-001 9.7062526662174770e-002 1.2956659089939432e-001 9.8680867671533157e-001</R>
</region>
<settings>
<property name="accuracy_tiepoints" value="1"/>
<property name="accuracy_cameras" value="10"/>
<property name="accuracy_cameras_ypr" value="2"/>
<property name="accuracy_markers" value="0.005"/>
<property name="accuracy_scalebars" value="0.001"/>
<property name="accuracy_projections" value="0.1"/>
</settings>
</chunk>
</document>
I'm only interested in reading the cameras node and their attributes, and I've used the following code for that, but it doesn't work:
using namespace std;
using namespace boost;
using namespace boost::property_tree;
const ptree& empty_ptree() {
static ptree t;
return t;
}
int main()
{
ptree tree;
read_xml(XML_PATH1, tree);
tree = tree.get_child("document.chunk", empty_ptree());
const ptree & formats = tree.get_child("cameras.camera", empty_ptree());
BOOST_FOREACH(const ptree::value_type & f, formats)
{
string at = f.first + ".<xmlattr>";
const ptree & attributes = f.second.get_child("<xmlattr>", empty_ptree());
cout << "Extracting attributes from " << at << ":" << endl;
BOOST_FOREACH(const ptree::value_type &v, attributes)
{
cout << "First: " << v.first.data() << " Second: " << v.second.data() << endl;
}
}
}

Answer 1

so, for each camera you want to iterate over each attribute, don't you ?
if yes, then you need to use equal_range() instead of get_child(); the latter returns a single child, the former a range of associative iterators pointing to all childs with the given key.
so, use get_child() to get document.chunk.cameras, use equal_range('camera') to get all cameras and for each camera use equal_range('xmlattr') to traverse its attributes.