6

lib/src/Startup.cpp

@@ -2,16 +2,21 @@
 
 #include <cstdlib>
 #include <iostream>
+#include <optional>
+#include <memory>
 #include <fstream>
 
 namespace aocpp {
 
-auto Startup(int argc, char ** argv) -> std::ifstream {
-  if (argc != 2) {
-    std::cerr << "Expected input file argument\n";
+auto Startup(int argc, char ** argv) -> std::istream& {
+  static std::ifstream fin;
+  switch (argc) {
+  case 2: fin = std::ifstream{argv[1]}; return fin;
+  case 1: return std::cin;
+  default:
+    std::cerr << "bad arguments\n";
     exit(EXIT_FAILURE);
   }
-  return std::ifstream{argv[1]};
 }
 
 }