Merge pull request #3931 from afabri/Stream_support-parseXML-GF

Stream_support:  Add example to read an xml file using boost::property_tree

Stream_support/doc/Stream_support/IOstream.txt

@@ -258,6 +258,24 @@ in those WKT types, namely:
 - `CGAL::Point_3`
 - `CGAL::Polygon_with_holes_2`
 - random access range of the above types.
+
+\section IOstreamXML Reading Adhoc XML
+
+In case you have to read data in a simple xml file with a simple structure, without existing I/O libraries
+the <a href="https://www.boost.org/doc/libs/release/libs/property_tree/">`boost::property_tree`</a> comes in handy.
+The following small example shows how to parse a file
+looking like this:
+
+    <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+    <PolySet>
+    	<Polygon>
+		<Point X="-715.8811978465" Y="-2729.9490000000" Z="-534.9000000000"/>
+		<Point X="-718.1905989232" Y="-2729.9490000000" Z="-538.9000000000"/>
+		<Point X="-722.8094010768" Y="-2729.9490000000" Z="-538.9000000000"/>
+        </Polygon>
+    </PolySet>
+
+\cgalExample{Stream_support/read_xml.cpp}
 */ 
 } /* namespace CGAL */
 

Stream_support/doc/Stream_support/examples.txt

@@ -2,4 +2,5 @@
 \example Stream_support/Linestring_WKT.cpp
 \example Stream_support/Point_WKT.cpp
 \example Stream_support/Polygon_WKT.cpp
+\example Stream_support/read_xml.cpp
 */

Stream_support/examples/Stream_support/CMakeLists.txt

@@ -26,6 +26,8 @@ if ( CGAL_FOUND )
     create_single_source_cgal_program( "Linestring_WKT.cpp" )
     create_single_source_cgal_program( "read_WKT.cpp" )
 
+    create_single_source_cgal_program( "read_xml.cpp" )
+  
 else ()
   message(STATUS "This project requires the CGAL library, and will not be compiled.")
   return()  

Stream_support/examples/Stream_support/data/cloud.pol

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<PolySet>
+	<Polygon>
+		<Point X="-715.8811978465" Y="-2729.9490000000" Z="-534.9000000000"/>
+		<Point X="-718.1905989232" Y="-2729.9490000000" Z="-538.9000000000"/>
+		<Point X="-722.8094010768" Y="-2729.9490000000" Z="-538.9000000000"/>
+        </Polygon>
+</PolySet>

Stream_support/examples/Stream_support/read_xml.cpp

@@ -0,0 +1,35 @@
+#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
+#include <boost/property_tree/ptree.hpp>
+#include <boost/property_tree/xml_parser.hpp>
+#include <vector>
+#include <fstream>
+
+typedef CGAL::Exact_predicates_inexact_constructions_kernel  K;
+typedef K::Point_3                                Point_3;
+
+int main(int argc, char* argv[]){
+  std::ifstream in( (argc>1)? argv[1] : "data/cloud.pol");
+  boost::property_tree::ptree tree;
+  boost::property_tree::read_xml(in, tree);
+
+  std::vector<Point_3> points;
+
+  for(boost::property_tree::ptree::value_type& node : tree.get_child("PolySet.Polygon")){
+    boost::property_tree::ptree subtree = node.second;         
+    if( node.first == "Point" ){
+      for( boost::property_tree::ptree::value_type const& v : subtree.get_child( "" ) ) {
+        std::string label = v.first;
+        
+        if ( label == "<xmlattr>" ) {
+          Point_3 p(subtree.get<double>( label+".X"),
+                    subtree.get<double>( label+".Y"),
+                    subtree.get<double>( label+".Z"));
+          points.push_back(p);
+        }
+      }
+    }
+  }    
+
+  std::cout << points.size() << " points read"<< std::endl;
+  return 0;
+}