Array element count in C

Question

I've always used following paradigm for iterating over statically-defined arrays in C:

struct foo { ... };
struct foo array[10];

for (int i; i < sizeof(array) / sizeof(array[0]); i++)
    ...

And, well, this worked every time so far ;-)

But it makes wonder, could this not break if the struct was actually of length that doesn't align naturally, e.g.:

struct foo { long a; char b; };

Shouldn't the compiler decide that sizeof(struct foo) == 7 while sizeof(array) == 32 due to alignment (LP64 data model)?

Answer 1

As the C99 standard, section 6.5.3.4 states about sizeof operator:

When applied to an operand that has array type, the result is the total number of bytes in the array.

And:

EXAMPLE 2 Another use of the sizeof operator is to compute the number of elements in an array:

     `sizeof array / sizeof array[0]`

So the size of array will always be a multiple of size of it's elements.

And from the same paragraph about structs:

When applied to an operand that has structure or union type, the result is the total number of bytes in such an object, including internal and trailing padding.

Answer 2

No.

There is no "dead space" in an array; if there's padding, it's included in the struct size.