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Could you please explain what ATOMIC_VAR_INIT is used for? I couldn't find any useful information on that (or maybe I just coulnd't get it). As far as I understood it is used to initialize atomic variables in some special way, but what kind of initialization is done? When it might be useful? All the examples I could find was
atomic<int> t = ATOMIC_VAR_INIT(2);
why not just
atomic<int> t = 2;
what's the difference?
atomic_int i(3);
in C, but you can writeatomic_int i=ATOMIC_VAR_INIT(3);
in both C and C++.Yes, that's right. Didn't think about that. Thank you.Another thing that can be done is putting atomic classes betweenCode: [Select]#pragma pack(push)
#pragma pack(4)
// class atomic ...
#pragma pack(pop)
That wouldn't help: it just affects the layout of the atomic objects, not the alignment of the whole object.
MSVC is inconsistent: with #pragma pack(1) it obeys the alignment requirements sometimes, but not others.Thanks.
gcc always ignores alignment requirements with #pragma pack(1).
I'll put asserts in the atomic ops.
Another thing that can be done is putting atomic classes betweenCode: [Select]#pragma pack(push)
#pragma pack(4)
// class atomic ...
#pragma pack(pop)
hmmm..
#pragma pack affects default alignment, but it shouldn't affect explicit alignment.
This code outputs 8 for the size and true for is_aligned call on my machine inspite of #pragma pack(1).Code: [Select]#include <iostream>I'm not sure about gcc.
#pragma pack(1)
struct X
{
char a;
__declspec (align(4)) long b;
};
bool is_aligned(void *ptr, int boundary)
{
return ((uintptr_t)ptr & (boundary - 1)) == 0;
}
int main()
{
X x;
std::cout << sizeof(X) << std::endl;
std::cout << is_aligned(&x.b, 4) << std::endl;
}
Anyway, if this is not portable enough then assert is good solution too.
#pragma pack(push)
#pragma pack(4)
// class atomic ...
#pragma pack(pop)