Improve command line parser.

2019/CMakeLists.txt

@@ -2,9 +2,11 @@ cmake_minimum_required(VERSION 3.15)
 
 project(aoc2019)
 
+find_package(Boost REQUIRED COMPONENTS program_options)
+
 add_library(AoCSolutions src/solutions.hpp src/solutions.cpp src/day01.cpp)
 target_compile_features(AoCSolutions PUBLIC cxx_std_17)
 
 add_executable(runner src/runner.cpp)
 target_compile_features(runner PUBLIC cxx_std_17)
-target_link_libraries(runner AoCSolutions)
+target_link_libraries(runner AoCSolutions Boost::program_options)

2019/src/runner.cpp

@@ -1,34 +1,48 @@
 #include "solutions.hpp"
 #include <iostream>
-#include <charconv>
-#include <cstring>
+#include <boost/program_options.hpp>
 
-template<typename Int, int Radix = 10>
-Int int_from_cstr(Int &value, const char *begin) {
-    const char *end = begin + std::strlen(begin);
-    auto result = std::from_chars(begin, end, value, Radix);
-    if (result.ec != std::errc()) {
-        throw std::invalid_argument("Unparseable integer");
-    }
+namespace po = boost::program_options;
 
-    return value;
+struct AoCOptions {
+    int day;
+    bool part2;
+};
+
+AoCOptions parse_options(const int argc, const char* argv[]) {
+    AoCOptions options{};
+    po::options_description desc("Allowed options");
+    desc.add_options()
+            ("day", po::value<int>(&options.day)->required(), "The day to run.")
+            ("part2,2", po::bool_switch(&options.part2), "Whether to run part 2.");
+
+    po::positional_options_description positionals;
+    positionals.add("day", 1);
+
+    po::variables_map vm;
+
+    po::store(po::command_line_parser(argc, argv).options(desc).positional(positionals).run(), vm);
+    po::notify(vm);
+
+    return options;
 }
 
 int main(int argc, const char *argv[]) {
-    if (argc < 2) {
-        std::cerr << "Specify a day to run.\n";
+    try {
+        const auto options = parse_options(argc, argv);
+
+        const aoc2019::solution_t solution = aoc2019::get_implementation(options.day, options.part2);
+        if (solution != nullptr) {
+            solution(std::cin, std::cout);
+            return 0;
+        } else {
+            std::cerr << "Unimplemented.\n";
+            return 1;
+        }
+    } catch (po::required_option &ignored) {
         return 1;
-    }
-
-    int day;
-    int_from_cstr(day, argv[1]);
-
-    const aoc2019::solution_t solution = aoc2019::get_implementation(day);
-    if (solution != nullptr) {
-        solution(std::cin, std::cout);
-        return 0;
-    } else {
-        std::cerr << "Unimplemented.\n";
+    } catch (std::out_of_range &ignored) {
+        std::cerr << "Invalid day.\n";
         return 1;
     }
 }