Add example of modifying an AST and printing out modified code

examples/func_defs_add_param.py

@@ -0,0 +1,58 @@
+#-----------------------------------------------------------------
+# pycparser: func_defs_add_param.py
+#
+# Example of rewriting AST nodes to add parameters to function
+# definitions. Adds an "int _hidden" to every function.
+#
+# Eli Bendersky [https://eli.thegreenplace.net/]
+# License: BSD
+#-----------------------------------------------------------------
+from __future__ import print_function
+import sys
+
+from pycparser import c_parser, c_ast, c_generator
+
+text = r"""
+void foo(int a, int b) {
+}
+
+void bar() {
+}
+"""
+
+
+class ParamAdder(c_ast.NodeVisitor):
+    def visit_FuncDecl(self, node):
+        ty = c_ast.TypeDecl(declname='_hidden',
+                            quals=[],
+                            type=c_ast.IdentifierType(['int']))
+        newdecl = c_ast.Decl(
+                    name='_hidden',
+                    quals=[],
+                    storage=[],
+                    funcspec=[],
+                    type=ty,
+                    init=None,
+                    bitsize=None,
+                    coord=node.coord)
+        if node.args:
+            node.args.params.append(newdecl)
+        else:
+            node.args = c_ast.ParamList(params=[newdecl])
+
+
+if __name__ == '__main__':
+    parser = c_parser.CParser()
+    ast = parser.parse(text)
+    print("AST before change:")
+    ast.show(offset=2)
+
+    v = ParamAdder()
+    v.visit(ast)
+
+    print("\nAST after change:")
+    ast.show(offset=2)
+
+    print("\nCode after change:")
+    generator = c_generator.CGenerator()
+    print(generator.visit(ast))