Overloaded delete operator bug

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2 total messages Started by Graeme Dixon Mon, 10 Apr 1989 12:26

#1837

Author: Graeme Dixon
Date: Mon, 10 Apr 1989 12:26

73 lines
1985 bytes

There is a bug in the code generated by g++ when the delete operator
is overloaded that results in the delete operator being called once for
each derived class in a hierarchy. The following program illustrates
the bug:

#include <stream.h>

class A
{
public:
    A()  { cout << "A::A\n"; }
    ~A() { cout << "A::~A\n"; }

    void* operator new(long size)  { cout << "A::new\n"; return malloc(size); }
    void operator delete(A* todel) { cout << "A::delete\n"; free(todel); }
};

class B: public A
{
public:
    B()  { cout << "B::B\n"; }
    ~B() { cout << "B::~B\n"; }
};

class C: public B
{
public:
    C()  { cout << "C::C\n"; }
    ~C() { cout << "C::~C\n"; }
};

main()
{
    B *b = new B;
    delete b;      // OK

    C *c = new C;
    delete c;      // not OK - delete called twice
}

and produces the following when compiled with g++ (version 1.34.0) and
linked with /usr/lib/debug/malloc.o (using
g++ -o bug bug.cc /usr/lib/debug/malloc.o):

A::new
A::A
B::B
B::~B
A::~A
A::delete
A::new
A::A
B::B
C::C
C::~C
B::~B
A::~A
A::delete
A::delete
free: block 0x21804 was already free

Abort (core dumped)

Each successively derived class results in an additional invocation of
the delete operator when an instance of that class is deleted.

Graeme Dixon -
  Computing Laboratory, University of Newcastle upon Tyne, UK

JANET = Graeme.Dixon@uk.ac.newcastle
ARPA  = GraemeDixon@newcastle.ac.uk
UUCP  = ...!ukc!newcastle.ac.uk!Graeme.Dixon
PHONE = +44 91 222 8067

Overloaded delete operator bug

#1844

Author: Michael Tiemann
Date: Mon, 10 Apr 1989 16:26

76 lines
2962 bytes

Here is a fix for GNU C++ wrt overloading operator delete.  Your line
numbers will vary.

yahi% diff -c2 cplus-init.c~ cplus-init.c
*** cplus-init.c~	Sun Apr  2 04:03:25 1989
--- cplus-init.c	Mon Apr 10 09:20:40 1989
***************
*** 2600,2603 ****
--- 2604,2608 ----
        tree exprstmt = NULL_TREE;
        tree parent_auto_delete = auto_delete;
+       tree cond;
  
        /* If this type does not have a destructor, but does have
***************
*** 2608,2616 ****
  	{
  	  parent_auto_delete = integer_zero_node;
! 	  expr = build_opfncall (DELETE_EXPR, addr, addr);
! 	  if (expr == error_mark_node)
! 	    return error_mark_node;
! 	  exprstmt = build_tree_list (NULL_TREE, expr);
  	}
  
        if (basetype && TYPE_NEEDS_DESTRUCTOR (basetype))
--- 2613,2641 ----
  	{
  	  parent_auto_delete = integer_zero_node;
! 	  if (auto_delete == integer_zero_node)
! 	    cond = NULL_TREE;
! 	  else
! 	    {
! 	      expr = build_opfncall (DELETE_EXPR, addr, addr);
! 	      if (expr == error_mark_node)
! 		return error_mark_node;
! 	      if (auto_delete != integer_one_node)
! 		cond = build (COND_EXPR, void_type_node,
! 			      build (NE_EXPR, integer_type_node, auto_delete, integer_zero_node),
! 			      expr,
! 			      build (NOP_EXPR, void_type_node, integer_zero_node));
! 	      else cond = expr;
! 	    }
! 	}
!       else if (basetype == NULL_TREE
! 	       || ! TYPE_NEEDS_DESTRUCTOR (basetype))
! 	{
! 	  cond = build (COND_EXPR, void_type_node,
! 			build (NE_EXPR, integer_type_node, auto_delete, integer_zero_node),
! 			build_function_call (BID, build_tree_list (NULL_TREE, addr)),
! 			build (NOP_EXPR, void_type_node, integer_zero_node));
  	}
+       if (cond)
+ 	exprstmt = build_tree_list (NULL_TREE, cond);
  
        if (basetype && TYPE_NEEDS_DESTRUCTOR (basetype))
***************
*** 2625,2639 ****
  				  exprstmt);
  	}
-       else
- 	{
- 	  tree cond = build (COND_EXPR, void_type_node,
- 			     build (NE_EXPR, integer_type_node, auto_delete, integer_zero_node),
- 			     (TREE_GETS_DELETE (type)
- 			      ? build_opfncall (DELETE_EXPR, addr, addr)
- 			      : build_function_call (BID, build_tree_list (NULL_TREE, addr))),
- 			     build (NOP_EXPR, void_type_node, integer_zero_node));
- 
- 	  exprstmt = build_tree_list (NULL_TREE, cond);
- 	}
  
        for (i = 2; i <= n_baseclasses; i++)
--- 2650,2653 ----


Michael

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