Function has corrupt return value

Question

I have a situation in Visual C++ 2008 that I have not seen before. I have a class with 4 STL objects (list and vector to be precise) and integers.

It has a method:

inline int id() { return m_id; }

The return value from this method is corrupt, and I have no idea why.

I'd like to believe its a stack smash, but as far as I know, I have no buffer over-runs or allocation issues.

Answer 1

You seem to be using a pointer to an invalid class somehow. The return value shown is the value that VS usually uses to initialize memory with:

2^32 - 842150451 = 0xCDCDCDCD

Answer 2

1. You probably have not initialized the class that this function is a member of.
2. Without seeing more of the code in context.. it might be that the m_id is out of the scope you expect it to be in.

Answer 3

I don't really know how best to post the code snippets I have , but here's my best shot at it. Please do let me know if they are insufficient:

Class DnsHeader has an object m_header inside DnsPacket.

Main body:

DnsPacket *p ;
p = new DnsPacket(r);
assert (_CrtCheckMemory());
p->add_bytes(buf, r); // add bytes to a vector m_bytes inside DnsPacket
if (p->parse())
{
read_packet(sin, *p);
}

p->parse:

size_t size = m_bytes.size(); // m_bytes is a vector
  unsigned char *bytes = new u_char[m_bytes.size()];
  copy(m_bytes.begin(), m_bytes.end(), bytes); 

m_header = new DnsHeader();
  eprintf("m_header allocated at %x\n", m_header);
  assert(_CrtCheckMemory());
  if (m_header->init(bytes, size)) // just set the ID and a bunch of other ints here.
{
    size_t pos = DnsHeader::SIZE; // const int
    if (pos != size)
      ; // XXX perhaps generate a warning about extraneous data?

    if (ok)
      m_parsed = true;

  }
  else
  {
    m_parsed = false;
  }

  if (!ok) {
    m_parsed = false;
  }
  return m_parsed;
}

read_packet:

  DnsHeader& h = p.header();
  eprintf("The header ID is %d\n", h.id()); // ID is wrong here
...

DnsHeader constructor:

m_id = -1;
  m_qdcount = m_ancount = m_nscount = m_arcount = 0;

  memset(&m_flags, 0, sizeof(m_flags)); // m_flags is a struct
  m_flags.rd = 1;

p.header():

return *m_header;

m_header->init: (u_char* bytes, int size)

header_fmt *h = (header_fmt *)bytes;
m_id = ntohs(h->id);
eprintf("Assigning an id of %d/%d\n", ntohs(h->id), m_id); // ID is correct here
m_qdcount = ntohs(h->qdcount);
m_ancount = ntohs(h->ancount);
m_nscount = ntohs(h->nscount);
m_arcount = ntohs(h->arcount);

Answer 4

Some more observations Here's something that puts me off. The debugger prints right values in the place mentioned // wrong ID.

  m_header = new DnsHeader();
  assert(_CrtCheckMemory());

  if (m_header->init(bytes, size))
  {
    eprintf("0The header ID is %d\n", m_header->id()); // wrong ID!!!

inside m_header->init()

 m_qdcount = ntohs(h->qdcount);
    m_ancount = ntohs(h->ancount);
    m_nscount = ntohs(h->nscount);
    m_arcount = ntohs(h->arcount);
    eprintf("The details are %d,%d,%d,%d\n", m_qdcount, m_ancount, m_nscount, m_arcount);

    // copy the flags
    // this doesn't work with a bitfield struct :(
    // memcpy(&m_flags, bytes + 2, sizeof(m_flags));
    //unpack_flags(bytes + 2); //TODO
    m_init = true;
  }
  eprintf("Assigning an id of %d\n", m_id); // Correct ID.
  return

m_header->id() is an inline function in the header file

inline int id() { return m_id; }

Answer 5

Reinstalled VC++. That fixed everything.

Thank you for your time and support everybody! :) Appreciate it!