factor out getopt processing

lib/src/Startup.cpp

@@ -4,6 +4,7 @@
 #include <iostream>
 #include <fstream>
 #include <utility>
+#include <optional>
 
 #include <libgen.h>
 #include <unistd.h>
@@ -11,54 +12,119 @@
 #define DOCTEST_CONFIG_IMPLEMENT
 #include <doctest.h>
 
-auto main(int argc, char ** argv) -> int
+namespace
 {
-  bool run_tests {};
-  char const* in_name {};
-  char const* out_name {};
 
-  try {
+  /// @brief Fields corresponding to command line options
+  struct Options
+  {
+    /// -i: Input file name or nullptr for stdin
+    char const *in_name;
+    /// -o: Output file name or nullptr for stdout
+    char const *out_name;
+    /// -t: Flag to run tests instead of solution
+    bool run_tests;
+    /// -h: Flag to print help and exit
+    bool print_help;
+  };
+
+  /// @brief Parse the basic command line options used by all solution programs
+  /// @param[in,out] argc argc from main
+  /// @param[in,out] argv argv from main
+  /// @return options structure on success
+  ///
+  /// `argc` and `argv` are updated to have the processed options removed from them
+  /// on a successful options parse.
+  auto ParseOptions(int &argc, char **&argv) -> std::optional<Options>
+  {
+    Options result{};
+
     int ch;
-    while ((ch = getopt(argc, argv, ":hi:o:t")) != -1) {
-      switch (ch) {
-        case 'i': in_name = optarg; break;
-        case 'o': out_name = optarg; break;
-        case 't': run_tests = true; break;
+    while ((ch = getopt(argc, argv, ":hi:o:t")) != -1)
+    {
+      switch (ch)
+      {
+      case 'i':
+        result.in_name = optarg;
+        break;
+      case 'o':
+        result.out_name = optarg;
+        break;
+      case 't':
+        result.run_tests = true;
+        break;
       case ':':
         std::cerr << "Missing argument to -" << char(optopt) << std::endl;
-          return 1;
+        return {};
       case 'h':
-          std::cerr << "Usage: " << basename(argv[0]) << " [-i INPUT] [-o OUTPUT] [-t]" << std::endl;
-          return 0;
+        result.print_help = true;
+        break;
       case '?':
       default:
         std::cerr << "Unknown flag -" << char(optopt) << std::endl;
-          return 1;
+        return {};
       }
     }
 
-    if (run_tests) {
+    // Consume the option command line arguments to prepare for
+    // additional subsequent consumers (like doctest)
+    argc -= optind;
+    argv += optind;
+
+    return result;
+  }
+
+} // namespace
+
+auto main(int argc, char **argv) -> int
+{
+  Options options;
+  if (auto o = ParseOptions(argc, argv))
+  {
+    options = *o;
+  }
+  else
+  {
+    return EXIT_FAILURE;
+  }
+
+  if (options.print_help)
+  {
+    std::cerr << "Usage: " << basename(argv[0]) << " [-i INPUT] [-o OUTPUT] [-t]" << std::endl;
+    return EXIT_SUCCESS;
+  }
+
+  if (options.run_tests)
+  {
     return doctest::Context{argc, argv}.run();
   }
 
+  // Establish input streams
   std::ifstream fin;
   std::ofstream fout;
-    std::istream & in  {in_name  ? fin  = std::ifstream{in_name } : std::cin };
-    std::ostream & out {out_name ? fout = std::ofstream{out_name} : std::cout};
+  std::istream &in{options.in_name ? fin = std::ifstream{options.in_name} : std::cin};
+  std::ostream &out{options.out_name ? fout = std::ofstream{options.out_name} : std::cout};
 
-    if (in.fail()) {
+  if (in.fail())
+  {
     std::cerr << "Bad input file" << std::endl;
-      return 1;
+    return EXIT_FAILURE;
   }
 
-    if (out.fail()) {
+  if (out.fail())
+  {
     std::cerr << "Bad output file" << std::endl;
-      return 1;
+    return EXIT_FAILURE;
   }
 
+  try
+  {
     Main(in, out);
-  } catch (std::exception const& e) {
-    std::cerr << "Program failed: " << e.what() << std::endl;
-    return 1;
+    return EXIT_SUCCESS;
+  }
+  catch (std::exception const &e)
+  {
+    std::cerr << "Solution failed: " << e.what() << std::endl;
+    return EXIT_FAILURE;
   }
 }