On Sat, Mar 10, 2012 at 12:10 AM, Manohar Vanga <manohar.vanga@gmail.com> wrote:
Also, from the archives: http://www.mail-archive.com/kernelnewbies@nl.linux.org/msg12320.html
Thank you for links which gives good explanation. But I am not able to understand the part accessing a member through NULL pointer like ((size_t) &((TYPE *)0)->MEMBER) How it is handled? In C code if we access a member through NULL pointer like this will cause the code to crash. Am I missing something?
On Fri, Mar 9, 2012 at 7:21 PM, Vijay Chauhan <kernel.vijay@gmail.com> wrote:
Hi,
I'm checking the container_of and offsetof macro
#define container_of(ptr, type, member) ({ \ const typeof( ((type *)0)->member ) *__mptr = (ptr); (type *)( (char *)__mptr - offsetof(type,member) );})
#define offsetof(TYPE, MEMBER) \ ((size_t) &((TYPE *)0)->MEMBER)
I did not understand the first line of both macro. Will it not create the NULL pointer dereference problem? I know it works and read some article but it did not explain this part, so can anyone explain why the NULL pointer error is not coming. Am I missing something? Any C language specification of such example.
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-- /manohar