sol2/examples/source/protected_functions.cpp

#define SOL_ALL_SAFETIES_ON 1
#include <sol/sol.hpp>

#include <iostream>

int main() {
	std::cout << "=== protected_functions ===" << std::endl;

	sol::state lua;
	lua.open_libraries(sol::lib::base);

	// A complicated function which can error out
	// We define both in terms of Lua code

	lua.script(R"(
			function handler (message)
				return "Handled this message: " .. message
			end

			function f (a)
				if a < 0 then
					error("negative number detected")
				end
				return a + 5
			end
		)");

	// Get a protected function out of Lua
	sol::protected_function f(lua["f"], lua["handler"]);

	sol::protected_function_result result = f(-500);
	if (result.valid()) {
		// Call succeeded
		int x = result;
		std::cout << "call succeeded, result is " << x << std::endl;
	}
	else {
		// Call failed
		sol::error err = result;
		std::string what = err.what();
		std::cout << "call failed, sol::error::what() is " << what << std::endl;
		// 'what' Should read 
		// "Handled this message: negative number detected"
	}

	std::cout << std::endl;
}