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I agree with you, but it'd be nicer if it were easier to figure this out from the standard --- either I'm missing something or else you have to infer it from re

I agree with you, but it'd be nicer if it were easier to figure this out from the standard --- either I'm missing something or else you have to infer it from reading between the lines: 6.7.2.1 para 15 of the C11 standard: Within a structure object, the non-bit-field members and the units in which bit-fields reside have addresses that increase in the order in which they are declared. A pointer to a structure object, suitably converted, points to its initial member (or if that member is a bit-field, then to the unit in which it resides), and vice versa. 6.7.2.1 para 17: There may be unnamed padding at the end of a structure or union. 6.2.5 para 20: An array type describes a contiguously allocated nonempty set of objects with a particular member object type, called the element type. http://www.open-std.org/jtc1/sc22/WG14/www/docs/n1570.pdf http://www.open-std.org/jtc1/sc22/WG14/www/docs/n1570.pdf So, on a platform with strict alignment, in order to achieve contiguous packing of structures (required by the last) and to achieve each structure member having a valid pointer (required by the first) the implementation must add enough optional padding (allowed by the middle) to make the size of the structure aligned. > You should also be using the fixed-width numeric types. I believe the parent is referring to the int8_t, int16_t types rather than the implementation-defined int, short, long types here.

vonmoltke 10y ago
> I agree with you, but it'd be nicer if it were easier to figure this out from the standard --- either I'm missing something or else you have to infer it from reading between the lines: > So, on a platform with strict alignment, in order to achieve contiguous packing of structures (required by the last) and to achieve each structure member having a valid pointer (required by the first) the implementation must add enough optional padding (allowed by the middle) to make the size of the structure aligned. It's not in the standard per se. It's a requirement for machine code to function on certain platforms. The standard basically just says that in all cases compilers have to generate machine code that works properly. It is imposed by the designers of the processor, not the C standard. > I believe the parent is referring to the int8_t, int16_t types rather than the implementation-defined int, short, long types here. This is indeed what I was talking about.

vonmoltke 10y ago

> I agree with you, but it'd be nicer if it were easier to figure this out from the standard --- either I'm missing something or else you have to infer it from reading between the lines: > So, on a platform with strict alignment, in order to achieve contiguous packing of structures (required by the last) and to achieve each structure member having a valid pointer (required by the first) the implementation must add enough optional padding (allowed by the middle) to make the size of the structure aligned. It's not in the standard per se. It's a requirement for machine code to function on certain platforms. The standard basically just says that in all cases compilers have to generate machine code that works properly. It is imposed by the designers of the processor, not the C standard. > I believe the parent is referring to the int8_t, int16_t types rather than the implementation-defined int, short, long types here. This is indeed what I was talking about.