Swift: How to use sizeof?

Question

In order to integrate with C API\'s while using Swift, I need to use the sizeof function. In C, this was easy. In Swift, I am in a labyrinth of type errors.

I have

Answer 1

Updated for Swift 3

Be careful that MemoryLayout.size means something different than sizeof in C/Obj-C. You can read this old thread https://devforums.apple.com/message/1086617#1086617

Swift uses an generic type to make it explicit that the number is known at compile time.

To summarize, MemoryLayout.size is the space required for a single instance while MemoryLayout.stride is the distance between successive elements in a contiguous array. MemoryLayout.stride in Swift is the same as sizeof(type) in C/Obj-C.

To give a more concrete example:

struct Foo {
  let x: Int
  let y: Bool
}

MemoryLayout.size      // returns 8 on 64-bit
MemoryLayout.size     // returns 1
MemoryLayout.size      // returns 9
MemoryLayout.stride    // returns 16 because of alignment requirements
MemoryLayout.alignment // returns 8, addresses must be multiples of 8