CODEWITHSUNDEEP
x86alignment
orpqK
orpqK

Reputation: 2785

Alignments on IA32 machine x86

enter image description here

Why are the offsets: 0 4 8 16 and 24? int = 4 bytes, double = 8 bytes. Why are there x's on the markings? How do you know when to use x's?

How does the other 2 structs and union offsets work?

Upvotes: 2

Views: 664

Answers (1)

paxdiablo
paxdiablo

Reputation: 881363

Because a data type generally aligns to its size. So a four-byte integer will usually begin on a multiple of four bytes. This is not always necessary but it's often an efficiency method. It is necessary in some architectures in that they'll actually crash (raise some sort of error) if you try to access misaligned data.

The reason you have the x characters is because they're the padding required to align the following data item.

Upvotes: 3

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