address changes on function call

[Evan]

Hi everyone,

I am experiencing the following strange and fatal behavior.  Given the
function below:

VectorN MatrixN::get_row1(unsigned i) const
{
  VectorN v;
  get_row2(i, v);
  return v;
}

The variable 'v' has the address '0x7ffff8c4d988'.  Stepping through
gdb to get_row2(), where 'v' is passed in by reference, reports:

MatrixN::get_row2 (this=0x7fff31c34940, i=0, result=@0x7fff31c34a50)

The address of 'v' (called 'result' in get_row2) has suddenly
changed!  Even stranger, 'print v' while in get_row1() indicates:

$4 = {
  _vptr.VectorN = 0x7fff31c34a50,
...
}

So, vptr (I assume this has to do with the fact that VectorN has
virtual methods) actually points to the address that is passed to
get_row2()!  Regardless of this occurrence, any changes that I make to
'result' in get_row2() do not show up as they should in 'v' in get_row1
().

Unfortunately, this behavior is not reproducible in a small test
program, just in my library of 70k lines of code :)

Any elucidation about what might be happening would be greatly
appreciated.

Thanks!
Evan