/tags/Root-branch-php-utl/SWIG/Examples/python/class/index.html

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

  8. 

  9. <tt>SWIG/Examples/python/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>
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  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) 
    24. 

  24. header file:
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  25. 

  26. <blockquote>
    27. 

  27. <pre>
    28. 

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

  30. class Shape {
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  31. public:
    32. 

  32.   Shape() {
    33. 

  33.     nshapes++;
    34. 

  34.   }
    35. 

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

  37.   };
    38. 

  38.   double  x, y;   
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  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:
    69. 

  69. 

  70. <blockquote>
    71. 

  71. <pre>
    72. 

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

  73. %module example
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  74. 

  75. %{
    76. 

  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 Python script</h2>
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  92. 

  93. Click <a href="example.py">here</a> to see a script that calls the C++ functions from Python.
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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>
    101. 

  101. <pre>
    102. 

  102. c = example.new_Circle(10.0)
    103. 

  103. </pre>
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  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
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  118. the member data was must be used.  In this case, <tt>Shape_x_get()</tt>
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  119. and <tt>Shape_x_set()</tt> are used since 'x' was defined in Shape.
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  120. 

  121. <p>
    122. 

  122. <li>To invoke a member function, you simply do this
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  123. 

  124. <blockquote>
    125. 

  125. <pre>
    126. 

  126. print "The area is ", example.Shape_area(c)
    127. 

  127. </pre>
    128. 

  128. </blockquote>
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  129. 

  130. <p>
    131. 

  131. <li>Type checking knows about the inheritance structure of C++. For example:
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  132. 

  133. <blockquote>
    134. 

  134. <pre>
    135. 

  135. example.Shape_area(c)       # Works (c is a Shape)
    136. 

  136. example.Circle_area(c)      # Works (c is a Circle)
    137. 

  137. example.Square_area(c)      # Fails (c is definitely not a Square)
    138. 

  138. </pre>
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  139. </blockquote>
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  140. 

  141. <p>
    142. 

  142. <li>To invoke a destructor, simply do this
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  143. 

  144. <blockquote>
    145. 

  145. <pre>
    146. 

  146. example.delete_Shape(c)     # Deletes a shape
    147. 

  147. </pre>
    148. 

  148. </blockquote>
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  149. 

  150. (Note: destructors are currently not inherited. This might change later).
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  151. 

  152. <p>
    153. 

  153. <li>Static member variables are wrapped as C global variables.  For example:
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  154. 

  155. <blockquote>
    156. 

  156. <pre>
    157. 

  157. n = example.cvar.Shape_nshapes     # Get a static data member
    158. 

  158. example.cvar.Shapes_nshapes = 13   # Set a static data member
    159. 

  159. </pre>
    160. 

  160. </blockquote>
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  161. 

  162. </ul>
    163. 

  163. 

  164. <h2>General Comments</h2>
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  165. 

  166. <ul>
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  167. <li>This low-level interface is not the only way to handle C++ code.
    168. 

  168. Shadow classes provide a much higher-level interface.
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  169. 

  170. <p>
    171. 

  171. <li>SWIG *does* know how to properly perform upcasting of objects in
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  172. an inheritance hierarchy (including multiple inheritance).  Therefore
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  173. it is perfectly safe to pass an object of a derived class to any
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  174. function involving a base class.
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  175. 

  176. <p>
    177. 

  177. <li>A wide variety of C++ features are not currently supported by SWIG.  Here is the
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  178. short and incomplete list:
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  179. 

  180. <p>
    181. 

  181. <ul>
    182. 

  182. <li>Overloaded methods and functions.  SWIG wrappers don't know how to resolve name
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  183. conflicts so you must give an alternative name to any overloaded method name using the
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  184. %name directive like this:
    185. 

  185. 

  186. <blockquote>
    187. 

  187. <pre>
    188. 

  188. void foo(int a);  
    189. 

  189. %name(foo2) void foo(double a, double b);
    190. 

  190. </pre>
    191. 

  191. </blockquote>
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  192. 

  193. <p>
    194. 

  194. <li>Overloaded operators.  Not supported at all. The only workaround for this is
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  195. to write a helper function. For example:
    196. 

  196. 

  197. <blockquote>
    198. 

  198. <pre>
    199. 

  199. %inline %{
    200. 

  200.     Vector *vector_add(Vector *a, Vector *b) {
    201. 

  201.           ... whatever ...
    202. 

  202.     }
    203. 

  203. %}
    204. 

  204. </pre>
    205. 

  205. </blockquote>
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  206. 

  207. <p>
    208. 

  208. <li>Namespaces.  Not supported at all. Won't be supported until SWIG2.0 (if at all).
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    210. 

  210. <p>
    211. 

  211. <li>Dave's snide remark: Like a large bottle of strong Tequilla, it's better to
    212. 

  212. use C++	in moderation.
    213. 

  213. 

  214. </ul>
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  215. 

  216. <hr>
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  217. </body>
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  218. </html>
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