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  1. <html>
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  2. <head>
    3. 

  3. <title>SWIG:Examples:tcl:class</title>
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  4. </head>
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  5. 

  6. <body bgcolor="#ffffff">
    7. 

  7. 

  8. 

  9. <tt>SWIG/Examples/tcl/class/</tt>
    10. 

  10. <hr>
    11. 

  11. 

  12. <H2>Wrapping a simple C++ class</H2>
    13. 

  13. 

  14. <p>
    15. 

  15. This example illustrates the most primitive form of C++ class wrapping performed
    16. 

  16. by SWIG.  In this case, C++ classes are simply transformed into a collection of
    17. 

  17. C-style functions that provide access to class members.
    18. 

  18. 

  19. <h2>The C++ Code</h2>
    20. 

  20. 

  21. Suppose you have some C++ classes described by the following (and admittedly lame) 
    22. 

  22. header file:
    23. 

  23. 

  24. <blockquote>
    25. 

  25. <pre>
    26. 

  26. /* File : example.h */
    27. 

  27. 

  28. class Shape {
    29. 

  29. public:
    30. 

  30.   Shape() {
    31. 

  31.     nshapes++;
    32. 

  32.   }
    33. 

  33.   virtual ~Shape() {
    34. 

  34.     nshapes--;
    35. 

  35.   };
    36. 

  36.   double  x, y;   
    37. 

  37.   void    move(double dx, double dy);
    38. 

  38.   virtual double area() = 0;
    39. 

  39.   virtual double perimeter() = 0;
    40. 

  40.   static  int nshapes;
    41. 

  41. };
    42. 

  42. 

  43. class Circle : public Shape {
    44. 

  44. private:
    45. 

  45.   double radius;
    46. 

  46. public:
    47. 

  47.   Circle(double r) : radius(r) { };
    48. 

  48.   virtual double area();
    49. 

  49.   virtual double perimeter();
    50. 

  50. };
    51. 

  51. 

  52. class Square : public Shape {
    53. 

  53. private:
    54. 

  54.   double width;
    55. 

  55. public:
    56. 

  56.   Square(double w) : width(w) { };
    57. 

  57.   virtual double area();
    58. 

  58.   virtual double perimeter();
    59. 

  59. };
    60. 

  60. </pre>
    61. 

  61. </blockquote>
    62. 

  62. 

  63. <h2>The SWIG interface</h2>
    64. 

  64. 

  65. A simple SWIG interface for this can be built by simply grabbing the header file
    66. 

  66. like this:
    67. 

  67. 

  68. <blockquote>
    69. 

  69. <pre>
    70. 

  70. /* File : example.i */
    71. 

  71. %module example
    72. 

  72. 

  73. %{
    74. 

  74. #include "example.h"
    75. 

  75. %}
    76. 

  76. 

  77. /* Let's just grab the original header file here */
    78. 

  78. %include "example.h"
    79. 

  79. </pre>
    80. 

  80. </blockquote>
    81. 

  81. 

  82. Note: when creating a C++ extension, you must run SWIG with the <tt>-c++</tt> option like this:
    83. 

  83. <blockquote>
    84. 

  84. <pre>
    85. 

  85. % swig -c++ -tcl example.i
    86. 

  86. </pre>
    87. 

  87. </blockquote>
    88. 

  88. 

  89. <h2>Some sample Tcl scripts</h2>
    90. 

  90. 

  91. SWIG performs two forms of C++ wrapping-- a low level interface and a high level widget-like interface.
    92. 

  92. <ul>
    93. 

  93. <li>
    94. 

  94. Click <a href="example1.tcl">here</a> to see a script that calls the C++ functions using the
    95. 

  95. low-level interface.
    96. 

  96. <li>
    97. 

  97. Click <a href="example2.tcl">here</a> to see a the same script written with the high-level
    98. 

  98. interface.
    99. 

  99. </ul>
    100. 

  100. 

  101. <h2>Key points</h2>
    102. 

  102. 

  103. <ul>
    104. 

  104. <li>The low-level C++ interface works like this:
    105. 

  105. <p>
    106. 

  106. <ul>
    107. 

  107. <li>To create a new object, you call a constructor like this:
    108. 

  108. 

  109. <blockquote>
    110. 

  110. <pre>
    111. 

  111. set c [new_Circle 10.0]
    112. 

  112. </pre>
    113. 

  113. </blockquote>
    114. 

  114. 

  115. <p>
    116. 

  116. <li>To access member data, a pair of accessor functions are used.
    117. 

  117. For example:
    118. 

  118. 

  119. <blockquote>
    120. 

  120. <pre>
    121. 

  121. Shape_x_set $c 15        ;# Set member data
    122. 

  122. set x [Shape_x_get $c]   ;# Get member data
    123. 

  123. </pre>
    124. 

  124. </blockquote>
    125. 

  125. 

  126. Note: when accessing member data, the name of the base class must
    127. 

  127. be used such as <tt>Shape_x_get</tt>
    128. 

  128. 

  129. <p>
    130. 

  130. <li>To invoke a member function, you simply do this
    131. 

  131. 

  132. <blockquote>
    133. 

  133. <pre>
    134. 

  134. puts "The area is [Shape_area $c]"
    135. 

  135. </pre>
    136. 

  136. </blockquote>
    137. 

  137. 

  138. <p>
    139. 

  139. <li>Type checking knows about the inheritance structure of C++. For example:
    140. 

  140. 

  141. <blockquote>
    142. 

  142. <pre>
    143. 

  143. Shape_area $c       # Works (c is a Shape)
    144. 

  144. Circle_area $c      # Works (c is a Circle)
    145. 

  145. Square_area $c      # Fails (c is definitely not a Square)
    146. 

  146. </pre>
    147. 

  147. </blockquote>
    148. 

  148. 

  149. <p>
    150. 

  150. <li>To invoke a destructor, simply do this
    151. 

  151. 

  152. <blockquote>
    153. 

  153. <pre>
    154. 

  154. delete_Shape $c     # Deletes a shape
    155. 

  155. </pre>
    156. 

  156. </blockquote>
    157. 

  157. 

  158. <p>
    159. 

  159. <li>Static member variables are wrapped as C global variables.  For example:
    160. 

  160. 

  161. <blockquote>
    162. 

  162. <pre>
    163. 

  163. set n $Shape_nshapes    # Get a static data member
    164. 

  164. set Shapes_nshapes 13   # Set a static data member
    165. 

  165. </pre>
    166. 

  166. </blockquote>
    167. 

  167. 

  168. </ul>
    169. 

  169. 

  170. <p>
    171. 

  171. <li>The high-level interface works like a Tk widget
    172. 

  172. 

  173. <p>
    174. 

  174. <ul>
    175. 

  175. <li>To create a new object, you call a constructor like this:
    176. 

  176. 

  177. <blockquote>
    178. 

  178. <pre>
    179. 

  179. Circle c 10      # c becomes a name for the Circle object
    180. 

  180. </pre>
    181. 

  181. </blockquote>
    182. 

  182. 

  183. <p>
    184. 

  184. <li>To access member data, use cget and configure methods.
    185. 

  185. For example:
    186. 

  186. 

  187. <blockquote>
    188. 

  188. <pre>
    189. 

  189. c configure -x 15        ;# Set member data
    190. 

  190. set x [c cget -x]        ;# Get member data
    191. 

  191. </pre>
    192. 

  192. </blockquote>
    193. 

  193. 

  194. <p>
    195. 

  195. <li>To invoke a member function, you simply do this
    196. 

  196. 

  197. <blockquote>
    198. 

  198. <pre>
    199. 

  199. puts "The area is [c area]"
    200. 

  200. </pre>
    201. 

  201. </blockquote>
    202. 

  202. 

  203. <p>
    204. 

  204. <li>To invoke a destructor, simply destroy the object name like this:
    205. 

  205. 

  206. <blockquote>
    207. 

  207. <pre>
    208. 

  208. rename c ""         # c goes away
    209. 

  209. </pre>
    210. 

  210. </blockquote>
    211. 

  211. 

  212. <p>
    213. 

  213. <li>Static member variables are wrapped as C global variables.  For example:
    214. 

  214. 

  215. <blockquote>
    216. 

  216. <pre>
    217. 

  217. set n $Shape_nshapes    # Get a static data member
    218. 

  218. set Shapes_nshapes 13   # Set a static data member
    219. 

  219. </pre>
    220. 

  220. </blockquote>
    221. 

  221. 

  222. </ul>
    223. 

  223. </ul>
    224. 

  224. 

  225. <h2>General Comments</h2>
    226. 

  226. 

  227. <ul>
    228. 

  228. <li>The low-level function interface is much faster than the high-level interface.
    229. 

  229. In fact, all the higher level interface does is call functions in the low-level interface.
    230. 

  230. 

  231. <p>
    232. 

  232. <li>SWIG *does* know how to properly perform upcasting of objects in an inheritance
    233. 

  233. hierarchy (including multiple inheritance).  Therefore it is perfectly safe to pass
    234. 

  234. an object of a derived class to any function involving a base class.
    235. 

  235. 

  236. <p>
    237. 

  237. <li>A wide variety of C++ features are not currently supported by SWIG.  Here is the
    238. 

  238. short and incomplete list:
    239. 

  239. 

  240. <p>
    241. 

  241. <ul>
    242. 

  242. <li>Overloaded methods and functions.  SWIG wrappers don't know how to resolve name
    243. 

  243. conflicts so you must give an alternative name to any overloaded method name using the
    244. 

  244. %name directive like this:
    245. 

  245. 

  246. <blockquote>
    247. 

  247. <pre>
    248. 

  248. void foo(int a);  
    249. 

  249. %name(foo2) void foo(double a, double b);
    250. 

  250. </pre>
    251. 

  251. </blockquote>
    252. 

  252. 

  253. <p>
    254. 

  254. <li>Overloaded operators.  Not supported at all. The only workaround for this is
    255. 

  255. to write a helper function. For example:
    256. 

  256. 

  257. <blockquote>
    258. 

  258. <pre>
    259. 

  259. %inline %{
    260. 

  260.     Vector *vector_add(Vector *a, Vector *b) {
    261. 

  261.           ... whatever ...
    262. 

  262.     }
    263. 

  263. %}
    264. 

  264. </pre>
    265. 

  265. </blockquote>
    266. 

  266. 

  267. <p>
    268. 

  268. <li>Namespaces.  Not supported at all. Won't be supported until SWIG2.0 (if at all).
    269. 

    270. 

  270. </ul>
    271. 

  271. 

  272. <hr>
    273. 

  273. </body>
    274. 

  274. </html>
    275. 

  275.