“That is either genius, or a seriously diseased mind.” – Linus Torvalds (opens in new tab)

(lkml.org)

76 pointssooham6y ago5 comments

5 comments

In that post Linus says something I don't understand in that post:

"... So with a constant, we have

  sizeof( 1 ? NULL : (int *) 1)

and the rule is that if one of the sides of a ternary operation with pointers is NULL, the end result is the other type (int *)."

Is Linus saying that the condition of the ternary operation doesn't matter if one of the sides is NULL? That it then always evaluates to the other side? That's not what happens when I try it. Or are there special rules when sizeof is applied?

roelschroeven6y ago

Oh, I get it now: Linus wasn't talking about the values, but about the types. In this case, the result will be a NULL pointer of type (int *).

Sorry, nothing to see here.

cbsks6y ago

I just had the same confusion. Thanks for figuring it out so I didn’t have to!

rurban6y ago

I really need this for libc optimizations. So far it only worked in C++ mode or newer clang's, but not in gcc.

msarnoff6y ago

Isn't this what GCC's `__builtin_constant_p()` does?

j / k navigate · click thread line to collapse

5 comments

roelschroeven6y ago

In that post Linus says something I don't understand in that post:

"... So with a constant, we have

  sizeof( 1 ? NULL : (int *) 1)

and the rule is that if one of the sides of a ternary operation with pointers is NULL, the end result is the other type (int *)."

roelschroeven6y ago

Oh, I get it now: Linus wasn't talking about the values, but about the types. In this case, the result will be a NULL pointer of type (int *).

Sorry, nothing to see here.

cbsks6y ago

I just had the same confusion. Thanks for figuring it out so I didn’t have to!

rurban6y ago

I really need this for libc optimizations. So far it only worked in C++ mode or newer clang's, but not in gcc.

msarnoff6y ago

Isn't this what GCC's `__builtin_constant_p()` does?

j / k navigate · click thread line to collapse