Add default argument methods

Author: optimisan

README.md

@@ -86,6 +86,14 @@ parser.run_and_exit_if_error();
 
 The only difference is that the `run_and_exit_if_error` method does not provide overloads for passing custom output and error streams. The `parse` method has overloads to support such scenarios. By default `std::cout` is used the regular output, e.g., the integrated help. Also `std::cerr` is used for displaying error messages.
 
+### Default Arguments
+To set and get default arguments (that do not need a name), use the `set_default` and `get_default` methods.
+
+```cpp
+parser.set_default<std::string>(false, "May be optional or required depending on the first parameter", "Default value");
+const auto default_argument = parser.get_default<std::string>();
+```
+
 ## Integrated help
 
 The parser comes with a pre-defined command that has the shorthand `-h` and the longhand `--help`. This is the integrated help, which appears if only a single command line argument is given, which happens to be either the shorthand or longhand form.

cmdparser.Test/catch.hpp

@@ -149,7 +149,38 @@ TEST_CASE( "Parse required bool provided but inverted", "[required] [bool] [avai
 
 	REQUIRE(ret == false);
 }
+TEST_CASE( "Parse default argument", "[default]") {
+	std::stringstream output { };
+	std::stringstream errors { };
+
+	const char* args[2] = {
+		"myapp",
+		"default_arg"
+	};
+	Parser parser(2, args);
+	parser.set_default<std::string>(true, "default argument");
+	const auto value = parser.run(output, errors);
+	REQUIRE(value == true);
+	REQUIRE(parser.app_name() == "myapp");
+	const auto ret = parser.get_default<std::string>();
+	REQUIRE(ret == "default_arg");
+}
 
+TEST_CASE( "Parse default argument with default value", "[default`] [missing]") {
+	std::stringstream output { };
+	std::stringstream errors { };
+
+	const char* args[1] = {
+		"myapp"
+	};
+	Parser parser(1, args);
+	parser.set_default<std::string>(false, "Optional default argument", "default_value");
+	const auto value = parser.run(output, errors);
+	REQUIRE(value == true);
+	REQUIRE(parser.app_name() == "myapp");
+	const auto ret = parser.get_default<std::string>();
+	REQUIRE(ret == "default_value");
+}
 TEST_CASE( "Parse required bool", "[required] [bool] [missing]" ) {
 	std::stringstream output { };
 	std::stringstream errors { };

cmdparser.Test/tests.cpp

@@ -358,8 +358,9 @@ namespace cli {
 		}
 
 		template<typename T>
-		void set_default(bool is_required, const std::string& description = "") {
+		void set_default(bool is_required, const std::string& description = "", T defaultValue = T()) {
 			auto command = new CmdArgument<T> { "", "", description, is_required, false };
+			command->value = defaultValue;
 			_commands.push_back(command);
 		}
 
@@ -488,6 +489,11 @@ namespace cli {
 			throw std::runtime_error("The parameter " + name + " could not be found.");
 		}
 
+		template<typename T>
+		T get_default() {
+			return get<T>("");
+		}
+
 		template<typename T>
 		T get_if(const std::string& name, std::function<T(T)> callback) const {
 			auto value = get<T>(name);