1 // Copyright 2012 Google Inc. 2 // All rights reserved. 3 // 4 // Redistribution and use in source and binary forms, with or without 5 // modification, are permitted provided that the following conditions are 6 // met: 7 // 8 // * Redistributions of source code must retain the above copyright 9 // notice, this list of conditions and the following disclaimer. 10 // * Redistributions in binary form must reproduce the above copyright 11 // notice, this list of conditions and the following disclaimer in the 12 // documentation and/or other materials provided with the distribution. 13 // * Neither the name of Google Inc. nor the names of its contributors 14 // may be used to endorse or promote products derived from this software 15 // without specific prior written permission. 16 // 17 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 18 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 19 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 20 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 21 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 22 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 23 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 24 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 25 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 26 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 27 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 28 29 /// \file examples/bindings.cpp 30 /// Showcases how to define Lua functions from C++ code. 31 /// 32 /// A major selling point of Lua is that it is very easy too hook native C and 33 /// C++ functions into the runtime environment so that Lua can call them. The 34 /// purpose of this example program is to show how this is done by using Lutok. 35 36 #include <cassert> 37 #include <cstdlib> 38 #include <iostream> 39 #include <map> 40 #include <sstream> 41 #include <stdexcept> 42 #include <string> 43 44 #include <lutok/exceptions.hpp> 45 #include <lutok/operations.hpp> 46 #include <lutok/state.ipp> 47 48 49 /// Calculates the factorial of a given number. 50 /// 51 /// \param i The postivie number to calculate the factorial of. 52 /// 53 /// \return The factorial of i. 54 static int 55 factorial(const int i) 56 { 57 assert(i >= 0); 58 59 if (i == 0) 60 return 1; 61 else 62 return i * factorial(i - 1); 63 } 64 65 66 /// A custom factorial function for Lua. 67 /// 68 /// \pre stack(-1) contains the number to calculate the factorial of. 69 /// \post stack(-1) contains the result of the operation. 70 /// 71 /// \param state The Lua state from which to get the function arguments and into 72 /// which to push the results. 73 /// 74 /// \return The number of results pushed onto the stack, i.e. 1. 75 /// 76 /// \throw std::runtime_error If the input parameters are invalid. Note that 77 /// Lutok will convert this exception to lutok::error. 78 static int 79 lua_factorial(lutok::state& state) 80 { 81 if (!state.is_number(-1)) 82 throw std::runtime_error("Argument to factorial must be an integer"); 83 const int i = state.to_integer(-1); 84 if (i < 0) 85 throw std::runtime_error("Argument to factorial must be positive"); 86 state.push_integer(factorial(i)); 87 return 1; 88 } 89 90 91 /// Program's entry point. 92 /// 93 /// \param argc Length of argv. Must be 2. 94 /// \param argv Command-line arguments to the program. The first argument to 95 /// the tool has to be a number. 96 /// 97 /// \return A system exit code. 98 int 99 main(int argc, char** argv) 100 { 101 if (argc != 2) { 102 std::cerr << "Usage: bindings <number>\n"; 103 return EXIT_FAILURE; 104 } 105 106 // Create a new Lua session and load the print() function. 107 lutok::state state; 108 state.open_base(); 109 110 // Construct a 'module' that contains an entry point to our native factorial 111 // function. A module is just a Lua table that contains a mapping of names 112 // to functions. Instead of creating a module by using our create_module() 113 // helper function, we could have used push_cxx_function on the state to 114 // define the function ourselves. 115 std::map< std::string, lutok::cxx_function > module; 116 module["factorial"] = lua_factorial; 117 lutok::create_module(state, "native", module); 118 119 // Use a little Lua script to call our native factorial function providing 120 // it the first argument passed to the program. Note that this will error 121 // out in a controlled manner if the passed argument is not an integer. The 122 // important thing to notice is that the exception comes from our own C++ 123 // binding and that it has been converted to a lutok::error. 124 std::ostringstream script; 125 script << "print(native.factorial(" << argv[1] << "))"; 126 try { 127 lutok::do_string(state, script.str(), 0, 0, 0); 128 return EXIT_SUCCESS; 129 } catch (const lutok::error& e) { 130 std::cerr << "ERROR: " << e.what() << '\n'; 131 return EXIT_FAILURE; 132 } 133 } 134