new graph_xml.hpp file to read (with libxml/parser) and write to XML

lib/graph/graph_xml.hpp

@@ -0,0 +1,74 @@
+#include <graph.hpp>
+
+#include <stdexcept>
+#include <fstream>
+
+#include <libxml/parser.h>
+#include <libxml/tree.h>
+
+namespace {
+
+template <typename V, typename F>
+void readVertices(Graph<V>& g,  F vertexCreator, const xmlNodePtr root_element)
+{
+  for (xmlNodePtr cur_node = root_element->children; cur_node; cur_node = cur_node->next)
+    if (cur_node->type == XML_ELEMENT_NODE) {
+
+      const std::string vertex( reinterpret_cast<const char*>(cur_node->properties->children->content));
+      V v = vertexCreator(vertex);
+
+      std::vector<V> edges;
+      for (xmlNodePtr cur_kid = cur_node->children; cur_kid; cur_kid = cur_kid->next)
+        if (cur_kid->type == XML_ELEMENT_NODE && cur_kid->children->type == XML_TEXT_NODE) {
+          const std::string e( reinterpret_cast<const char*>(cur_kid->children->content));
+          edges.push_back(vertexCreator(e));
+        }
+
+      g.setEdges(v, edges);
+    }
+}
+
+} // anonym namespace
+
+template <typename V, typename F>
+Graph<V> readGraphFromXML(const std::string& filename, F vertexCreator)
+{
+  xmlDocPtr doc = xmlReadFile(filename.c_str(), NULL, 0);
+  if (doc == NULL)
+    throw std::runtime_error("Failed to parse " + filename);
+
+  xmlNodePtr root_element = NULL;
+  root_element = xmlDocGetRootElement(doc);
+
+  Graph<V> g;
+  readVertices(g, vertexCreator, root_element);
+
+  xmlFreeDoc(doc);
+  xmlCleanupParser();
+  return g;
+}
+
+template <typename V, typename F>
+void writeGraphToXML(const Graph<V>& g, const std::string& filename, F vertexSerializer)
+{
+  std::ofstream file;
+  file.open (filename);
+  if (!file.is_open())
+    throw std::runtime_error("Failed to open " + filename + " to write.");
+
+  file << "<?xml version=\"1.0\" encoding=\"UTF-8\"?>" << std::endl;
+  file << "<graph>" << std::endl;
+
+  for (const auto cit : g) {
+    const std::string v = vertexSerializer(cit);
+    file << "<vertex pos=\"" << v << "\">" << std::endl;
+    for (const auto cit2 : g.neighboursOf(cit)) {
+      const std::string n = vertexSerializer(cit2);
+      file << "  <edge>" << v << "</edge>" << std::endl;
+    }
+    file << "</vertex>" << std::endl;
+  }
+
+  file << "</graph>" << std::endl;
+  file.close();
+}