How a reference address become NULL in C++?

Question

I have a coredump,it shows a reference address is NULL....

details:

(gdb) bt
#0  0xffffe410 in __kernel_vsyscall ()
#1  0x005b6c10 in raise () from /lib/libc.so.6
#2  0x005b8521 in abort () from /lib/libc.so.6
#3  0xf749e641 in Application::fatalSignal () at Application.cc:277
#4  <signal handler called>
#5  SdlProcess::procedureReturn (this=0x0, aSignal=0, aArg1=1, aArg2=0x0)
    at /include/c++/4.1.1/bits/stl_list.h:652
#6  0x08112edb in Sdl::authFailurer (aSdlProcess=@0x0, aLabel=0, aSignal=0, arg2=0x0) at /Mgr/SdlAuth.cc:1781
#7  0x00000000 in ?? ()
================
define:
Sdl::authFailurer(SdlProcess& aSdlProcess, int aLabel, int aSignal, int /*arg1*/, void* arg2)

#5 aSdlProcess.procedureReturn(0, 1, 0);

and in stl_list.h:652

 bool empty() const

      { return this->_M_impl._M_node._M_next == &this->_M_impl._M_node; }    ---->652
in procedureReturn()
{
   ...
  if (!mProcedureStack.empty())---->here,mProcedureStack is a datamember of SdlProcess
   ...
  {
  ...}
}

A reference can only become NULL through undefined behaviour, such as dereferencing a NULL pointer. — Seth Carnegie
– Seth Carnegie, Commented Sep 26, 2012 at 3:14

Mark Ransom · Accepted Answer · 2012-09-26 03:16:44Z

1

You can get a NULL reference by dereferencing a NULL pointer. I'm not sure how that could happen in this particular case, unless mProcedureStack is a reference.

answered Sep 26, 2012 at 3:16

Mark Ransom

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1 Comment

yiweng Over a year ago

list<SdlProcedureStatus*> mProcedureStack;

epsalon · Accepted Answer · 2012-09-26 03:16:55Z

1

The most often cause of this problem is when you return a dangling reference, such as:

int& foo() {
   int bar = 5;
   return bar;
}

The returned reference for foo now points to the stack and will contain undefined data.

answered Sep 26, 2012 at 3:16

epsalon

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