[Assorted-commits] SF.net SVN: assorted:[1058] sandbox/trunk/src/cc/overload_new.cc

[<yan...@us...>]

Revision: 1058
          http://assorted.svn.sourceforge.net/assorted/?rev=1058&view=rev
Author:   yangzhang
Date:     2008-11-06 05:09:46 +0000 (Thu, 06 Nov 2008)

Log Message:
-----------
added demo of overloading new

Added Paths:
-----------
    sandbox/trunk/src/cc/overload_new.cc

Added: sandbox/trunk/src/cc/overload_new.cc
===================================================================
--- sandbox/trunk/src/cc/overload_new.cc	                        (rev 0)
+++ sandbox/trunk/src/cc/overload_new.cc	2008-11-06 05:09:46 UTC (rev 1058)
@@ -0,0 +1,76 @@
+// Great thread: http://bytes.com/forum/thread521533.html
+//
+// - "operator new" != "new operator"
+//   - "new operator" consists of (1) allocation and (2) construction
+//   - "operator new" is the (1) allocation in "new operator"
+//
+// See also: man g++, search for -fcheck-new
+
+// #include <cstddef> // size_t
+#include <new> // bad_alloc, size_t
+#include <cstdlib> // malloc
+#include <iostream> // cout, endl
+
+// You can globally *replace* operator new.  There are two ways to replace
+// operator new.
+
+#if 1
+
+// Option 1: You can throw an exception when something goes awry.
+
+void *
+operator new(std::size_t sz) throw(std::bad_alloc)
+{
+  std::cout << "calling operator new that throws exceptions" << std::endl;
+  // If you uncomment this line, the compiler will complain.
+  // return NULL;
+  void *p = malloc(sz);
+  if (!p) throw std::bad_alloc();
+  return p;
+}
+
+#else
+
+// Option 2: You can return NULL when something goes awry.
+
+void *
+operator new(std::size_t sz) throw()
+{
+  std::cout << "calling operator new that returns NULL" << std::endl;
+  return malloc(sz);
+}
+
+#endif
+
+// You can also *overload* operator new for a specific class.  As with global
+// replacement, you can either go with a NULL-returning new or an
+// exception-throwing new.
+
+class C
+{
+  public:
+    int x;
+
+    void *
+    operator new(std::size_t sz) throw(std::bad_alloc)
+    {
+      std::cout << "calling C::operator new" << std::endl;
+      // Must use ::, otherwise will recurse into self infinitely.
+      return ::operator new(sz);
+    }
+};
+
+int
+main()
+{
+  // You can actually call operator new directly anywhere.
+  void *p = operator new(1024);
+  C *c = new C;
+  return 0;
+}
+
+// Output:
+//
+// calling operator new that throws exceptions
+// calling C::operator new
+// calling operator new that throws exceptions


This was sent by the SourceForge.net collaborative development platform, the world's largest Open Source development site.