Changes from Version 1 of DontReturnStackDelegateExample

Author:

jcc7 (IP: 68.97.93.38)

Timestamp:

11/12/05 05:05:59 (18 years ago)

Comment:

--

DontReturnStackDelegateExample

@@ +1 @@
+= Don't Return a Stack Delegate =
+
+''Part of'' DelegateCategory
+
+== Description ==
+
+This shows code that is '''broken''', namely returning a stack delegate from a function.
+
+== Example ==
+
+{{{
+#!d
+
+/* NOTE NOTE NOTE
+ *
+ * THIS CODE IS BROKEN.  This is an example of something that you
+ * should NOT do!
+ *
+ * You can never return a stack delegate because the data pointer of that
+ * delegate points to the stack frame where the delegate was created.  Once
+ * you return from the function, that stack frame goes away and the memory
+ * is reused by some other function.
+ *
+ * Most likely, when you call this stack delegate, your program won't crash
+ * (since the pointer points to a valid address in the stack), but you will be
+ * reading trash values, since the memory has been reused by some other
+ * function.
+ *
+ * Of course, if one of the variables is a pointer, then you would crash when
+ * you read & follow the pointer that is no longer valid.
+ */
+
+import std.stdio;
+
+int delegate() foo() {
+    int a = 1;
+    int b = 2;
+
+    writefln("int delegate() foo() is called. Locals a = %d, b = %d", a, b);
+    writefln("BUG!  You must NEVER return a stack delegate!");
+
+    return delegate int() { return a+b; };
+}
+
+
+int main() { 
+    foo();
+    return 0;
+}
+}}}
+
+== Source ==
+
+Original contribution by Russ Lewis. Changed based on suggestions by Blandger.
+
+|| Link || http://www.dsource.org/tutorials/index.php?show_example=109 ||
+|| Edited by || jcc7 ||
+|| Date/Time || Thu Jul 29, 2004 9:42 pm ||