[lib] fixed the bug on rr graph io. Should use temp_string_

Author: tangxifan

libs/librrgraph/src/io/gen/rr_graph_uxsdcxx.h

@@ -4020,7 +4020,7 @@ inline void write_node(T &in, std::ostream &os, Context &context){
 		auto child_context = in.get_node_loc(context);
 		os << "<loc";
 		os << " layer=\"" << in.get_node_loc_layer(child_context) << "\"";
-		os << " ptc=\"" << std::string(in.get_node_loc_ptc(child_context)) << "\"";
+		os << " ptc=\"" << in.get_node_loc_ptc(child_context) << "\"";
 		if((bool)in.get_node_loc_side(child_context))
 			os << " side=\"" << lookup_loc_side[(int)in.get_node_loc_side(child_context)] << "\"";
 		if((bool)in.get_node_loc_twist(child_context))

libs/librrgraph/src/io/rr_graph_uxsdcxx_serializer.h

@@ -713,7 +713,8 @@ class RrGraphSerializer final : public uxsd::RrGraphBase<RrGraphContextTypes> {
     }
 
     inline const char* get_node_loc_ptc(const t_rr_node& node) final {
-        return rr_graph_builder_->node_ptc_nums_to_string(node.id()).c_str();
+        temp_string_ = rr_graph_builder_->node_ptc_nums_to_string(node.id());
+        return temp_string_.c_str();
     }
     inline int get_node_loc_layer(const t_rr_node& node) final {
         return rr_graph_->node_layer(node.id());