[cfe-dev] sizeof(sizeof(...))

Mike Stump mrs at apple.com
Sat Dec 15 01:31:20 PST 2007

On Dec 14, 2007, at 12:30 PM, Ted Kremenek wrote:
> Does anyone have any insights on the semantics of expressions of the  
> form sizeof(sizeof(...))?

As you suspected the argument isn't evaluated because the type of the  
argument isn't a variable length array.  Put on your recursion hat and  
just think about the first bit of the operand....

sizeof (...)  has type size_t.

size_t isn't a VLA.

no need to consider anything instead of the (...).

For fun, try the follow on the old gray matter:

struct { char o[n][m]; } foo(int n, int m) { }

int main() {
   return sizeof(foo(3,4));


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