Added logic and unit tests for the required flag in mutex_args

README.md

@@ -25,6 +25,7 @@
           *    [Deciding if the value was given by the user](#deciding-if-the-value-was-given-by-the-user)
           *    [Joining values of repeated optional arguments](#joining-values-of-repeated-optional-arguments)
           *    [Repeating an argument to increase a value](#repeating-an-argument-to-increase-a-value)
+          *    [Mutually Exclusive Group](#mutually-exclusive-group)
      *    [Negative Numbers](#negative-numbers)
      *    [Combining Positional and Optional Arguments](#combining-positional-and-optional-arguments)
      *    [Printing Help](#printing-help)
@@ -280,6 +281,23 @@ program.parse_args(argc, argv);    // Example: ./main -VVVV
 std::cout << "verbose level: " << verbosity << std::endl;    // verbose level: 4
 ```
 
+#### Mutually Exclusive Group
+
+Create a mutually exclusive group using `program.add_mutually_exclusive_group(required = false)`. `argparse`` will make sure that only one of the arguments in the mutually exclusive group was present on the command line:
+
+```cpp
+auto &group = program.add_mutually_exclusive_group();
+group.add_argument("--first");
+group.add_argument("--second");
+```
+
+with the following usage will yield an error:
+
+```console
+foo@bar:/home/dev/$ ./main --first 1 --second 2
+Argument '--second VAR' not allowed with '--first VAR'
+```
+
 ### Negative Numbers
 
 Optional arguments start with ```-```. Can ```argparse``` handle negative numbers? The answer is yes!

include/argparse/argparse.hpp

@@ -1588,6 +1588,25 @@ class ArgumentParser {
                                    mutex_argument_it->get_usage_full() + "'");
         }
       }
+
+      if (!mutex_argument_used && group.m_required) {
+        // at least one argument from the group is
+        // required
+        std::string argument_names{};
+        std::size_t i = 0;
+        std::size_t size = group.m_elements.size();
+        for (Argument *arg : group.m_elements) {
+          if (i + 1 == size) {
+            // last
+            argument_names += "'" + arg->get_usage_full() + "' ";
+          } else {
+            argument_names += "'" + arg->get_usage_full() + "' or ";
+          }
+          i += 1;
+        }
+        throw std::runtime_error("One of the arguments " + argument_names +
+                                 "is required");
+      }
     }
   }
 

test/test_mutually_exclusive_group.cpp

@@ -21,6 +21,37 @@ TEST_CASE("Create mutually exclusive group with 2 arguments" *
       std::runtime_error);
 }
 
+TEST_CASE(
+    "Create mutually exclusive group with 2 arguments with required flag" *
+    test_suite("mutex_args")) {
+  argparse::ArgumentParser program("test");
+
+  auto &group = program.add_mutually_exclusive_group(true);
+  group.add_argument("--first");
+  group.add_argument("--second");
+
+  REQUIRE_THROWS_WITH_AS(
+      program.parse_args({"test"}),
+      "One of the arguments '--first VAR' or '--second VAR' is required",
+      std::runtime_error);
+}
+
+TEST_CASE(
+    "Create mutually exclusive group with 3 arguments with required flag" *
+    test_suite("mutex_args")) {
+  argparse::ArgumentParser program("test");
+
+  auto &group = program.add_mutually_exclusive_group(true);
+  group.add_argument("--first");
+  group.add_argument("--second");
+  group.add_argument("--third");
+
+  REQUIRE_THROWS_WITH_AS(program.parse_args({"test"}),
+                         "One of the arguments '--first VAR' or '--second VAR' "
+                         "or '--third VAR' is required",
+                         std::runtime_error);
+}
+
 TEST_CASE(
     "Create mutually exclusive group with 2 arguments, then copy the parser" *
     test_suite("mutex_args")) {