/tags/rel-1-3-24/SWIG/Examples/perl5/class/index.html

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  3. <title>SWIG:Examples:perl5:class</title>
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  7. 

  8. 

  9. <tt>SWIG/Examples/perl5/class/</tt>
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  10. <hr>
    11. 

  11. 

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

  13. 

  14. <tt>$Header$</tt><br>
    15. 

  15. 

  16. <p>
    17. 

  17. This example illustrates the most primitive form of C++ class wrapping performed
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  18. by SWIG.  In this case, C++ classes are simply transformed into a collection of
    19. 

  19. C-style functions that provide access to class members.
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  20. 

  21. <h2>The C++ Code</h2>
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  22. 

  23. Suppose you have some C++ classes described by the following (and admittedly lame) 
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  24. header file:
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  25. 

  26. <blockquote>
    27. 

  27. <pre>
    28. 

  28. /* File : example.h */
    29. 

  29. 

  30. class Shape {
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  31. public:
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  32.   Shape() {
    33. 

  33.     nshapes++;
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  34.   }
    35. 

  35.   virtual ~Shape() {
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  36.     nshapes--;
    37. 

  37.   };
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  38.   double  x, y;   
    39. 

  39.   void    move(double dx, double dy);
    40. 

  40.   virtual double area() = 0;
    41. 

  41.   virtual double perimeter() = 0;
    42. 

  42.   static  int nshapes;
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  43. };
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  44. 

  45. class Circle : public Shape {
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  46. private:
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  47.   double radius;
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  48. public:
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  49.   Circle(double r) : radius(r) { };
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  50.   virtual double area();
    51. 

  51.   virtual double perimeter();
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  52. };
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  53. 

  54. class Square : public Shape {
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  55. private:
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  56.   double width;
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  57. public:
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  58.   Square(double w) : width(w) { };
    59. 

  59.   virtual double area();
    60. 

  60.   virtual double perimeter();
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  61. };
    62. 

  62. </pre>
    63. 

  63. </blockquote>
    64. 

  64. 

  65. <h2>The SWIG interface</h2>
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  66. 

  67. A simple SWIG interface for this can be built by simply grabbing the header file
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  68. like this:
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  69. 

  70. <blockquote>
    71. 

  71. <pre>
    72. 

  72. /* File : example.i */
    73. 

  73. %module example
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  74. 

  75. %{
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  76. #include "example.h"
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  77. %}
    78. 

  78. 

  79. /* Let's just grab the original header file here */
    80. 

  80. %include "example.h"
    81. 

  81. </pre>
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  82. </blockquote>
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  83. 

  84. Note: when creating a C++ extension, you must run SWIG with the <tt>-c++</tt> option like this:
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  85. <blockquote>
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  86. <pre>
    87. 

  87. % swig -c++ -python example.i
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  88. </pre>
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  89. </blockquote>
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  90. 

  91. <h2>A sample Perl script</h2>
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  92. 

  93. Click <a href="runme.pl">here</a> to see a script that calls the C++ functions from Perl.
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  94. 

  95. <h2>Key points</h2>
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  96. 

  97. <ul>
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  98. <li>To create a new object, you call a constructor like this:
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  99. 

  100. <blockquote>
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  101. <pre>
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  102. $c = example::new_Circle(10.0);
    103. 

  103. </pre>
    104. 

  104. </blockquote>
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  105. 

  106. <p>
    107. 

  107. <li>To access member data, a pair of accessor functions are used.
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  108. For example:
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  109. 

  110. <blockquote>
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  111. <pre>
    112. 

  112. example::Shape_x_set($c,15);    # Set member data
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  113. $x = example::Shape_x_get($c);   # Get member data
    114. 

  114. </pre>
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  115. </blockquote>
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  116. 

  117. Note: when accessing member data, the name of the class in which
    118. 

  118. the data member is defined is used.  For example <tt>Shape_x_get()</tt>.
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  119. 

  120. <p>
    121. 

  121. <li>To invoke a member function, you simply do this
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  122. 

  123. <blockquote>
    124. 

  124. <pre>
    125. 

  125. print "The area is ", example::Shape_area($c);
    126. 

  126. </pre>
    127. 

  127. </blockquote>
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  128. 

  129. <p>
    130. 

  130. <li>Type checking knows about the inheritance structure of C++. For example:
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  131. 

  132. <blockquote>
    133. 

  133. <pre>
    134. 

  134. example::Shape_area($c);       # Works (c is a Shape)
    135. 

  135. example::Circle_area($c);      # Works (c is a Circle)
    136. 

  136. example::Square_area($c);      # Fails (c is definitely not a Square)
    137. 

  137. </pre>
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  138. </blockquote>
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  139. 

  140. <p>
    141. 

  141. <li>To invoke a destructor, simply do this
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  142. 

  143. <blockquote>
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  144. <pre>
    145. 

  145. example::delete_Shape($c);     # Deletes a shape
    146. 

  146. </pre>
    147. 

  147. </blockquote>
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  148. 

  149. <p>
    150. 

  150. <li>Static member variables are wrapped as C global variables.  For example:
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  151. 

  152. <blockquote>
    153. 

  153. <pre>
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  154. $n = $example::Shape_nshapes;     # Get a static data member
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  155. $example::Shapes_nshapes = 13;   # Set a static data member
    156. 

  156. </pre>
    157. 

  157. </blockquote>
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  158. 

  159. </ul>
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  160. 

  161. <h2>General Comments</h2>
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  162. 

  163. <ul>
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  164. <li>This low-level interface is not the only way to handle C++ code.  Shadow classes
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  165. provide a much higher-level interface.
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  166. 

  167. <p>
    168. 

  168. <li>SWIG *does* know how to properly perform upcasting of objects in an inheritance
    169. 

  169. hierarchy (including multiple inheritance).  Therefore it is perfectly safe to pass
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  170. an object of a derived class to any function involving a base class.
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  171. 

  172. <p>
    173. 

  173. <li>A wide variety of C++ features are not currently supported by SWIG.  Here is the
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  174. short and incomplete list:
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  175. 

  176. <p>
    177. 

  177. <ul>
    178. 

  178. <li>Overloaded methods and functions.  SWIG wrappers don't know how to resolve name
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  179. conflicts so you must give an alternative name to any overloaded method name using the
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  180. %name directive like this:
    181. 

  181. 

  182. <blockquote>
    183. 

  183. <pre>
    184. 

  184. void foo(int a);  
    185. 

  185. %name(foo2) void foo(double a, double b);
    186. 

  186. </pre>
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  187. </blockquote>
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  188. 

  189. <p>
    190. 

  190. <li>Overloaded operators.  Not supported at all. The only workaround for this is
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  191. to write a helper function. For example:
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  192. 

  193. <blockquote>
    194. 

  194. <pre>
    195. 

  195. %inline %{
    196. 

  196.     Vector *vector_add(Vector *a, Vector *b) {
    197. 

  197.           ... whatever ...
    198. 

  198.     }
    199. 

  199. %}
    200. 

  200. </pre>
    201. 

  201. </blockquote>
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  202. 

  203. <p>
    204. 

  204. <li>Namespaces.  Not supported at all. Won't be supported until SWIG2.0 (if at all).
    205. 

    206. 

  206. </ul>
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  207. 

  208. <hr>
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  209. </body>
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  210. </html>
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