Re: [Mingw-users] Variable Initialization

[J. G. <jg-...@jg...>]

Hi,

on the 29/04/04 16:12, Michael Gerdau wrote:
>> #include <iostream>
>> int main (void)
>> {
>>   int x;
>>   int *y = new int;
>>   std::cout << x << y;
>>   delete y;
>>   return 0;
>> }
>> 
>> What should it print? Zeros? Anything it wants?
> 
> For x definitely anything it wants.

Unless x ends up in the .bss section (which depends on compilation and
linking specifics), you could check this using objectdump and looking at
the symbol.  BSS section is zeroed upon load by expansion, as these are
all considered 0.

> For y I could imagine the memory to be initialized with 0.

The new operator is just simple memory allocation wrapper (likely even
just malloc in many cases), and malloc does not set to zero.  You could
create a "new" which did zero, it would be like this:

void * operator new_cleared(std::size_t size) throw (std::bad_alloc)
{
	void * result = calloc(size, 1);
	
	// if calloc was unable to allocate and clear (NULL returned),
	// then throw exception
	// (could check errno to be sure!)
     	if (result != NULL)
	{
         	throw std::bad_alloc();
	}

	return result;
};

// this is untested


You could even create a "renew" operator too, as C++ lacks this because
they prefer the use of containers instead of functions and classes
managing their own memory.  A renew operator could work with a realloc()
style allocator.


Kind regards

JG