使用Xcode Playground的Swift代码中的EXC_I386_GPFLT

Question

I ran the same code in Xcode 7beta/rc Playground project and got an error:

Execution was interrupted, reason: EXC_BAD_ACCESS(code=EXC_I386_GPFLT)

in

let n: Int = Int(Process.arguments[1])!

How do I solve in Playground project since other solutions don't seem to be related?

Binary tree: http://benchmarksgame.alioth.debian.org/u64q/program.php?test=binarytrees&lang=swift&id=1

class TreeNode {
    var left, right : TreeNode?
    var item : Int

    init(_ left: TreeNode?, _ right: TreeNode?, _ item: Int) {
        self.left = left
        self.right = right
        self.item = item
    }

    func check() -> Int {
        guard let left = left, let right = right else {
            return item
        }
        return item + left.check() - right.check()
    }
}

func bottomUpTree(item: Int, _ depth: Int) -> TreeNode {
    if depth > 0 {
        return
            TreeNode(
                bottomUpTree(2*item-1, depth-1),
                bottomUpTree(2*item, depth-1),
                item
        )
    }
    else {
        return
            TreeNode(nil,nil,item)
    }
}


let n: Int = Int(Process.arguments[1])!
let minDepth = 4
let maxDepth = n
let stretchDepth = n + 1

let check = bottomUpTree(0,stretchDepth).check()
print("stretch tree of depth \(stretchDepth)\t check: \(check)")

let longLivedTree = bottomUpTree(0,maxDepth)

var depth = minDepth
while depth <= maxDepth {
    let iterations = 1 << (maxDepth - depth + minDepth)
    var check = 0
    for i in 0..<iterations {
        check += bottomUpTree(i,depth).check()
        check += bottomUpTree(-i,depth).check()
    }
    print("\(iterations*2)\t trees of depth \(depth)\t check: \(check)")
    depth += 2
}

print("long lived tree of depth \(maxDepth)\t check: \(longLivedTree.check())")

Answer 1

Process.arguments holds the value that is passed as arguments for a command-line application.

But you're using it in a Playground: there's no access to command line input from a Playground (they are Sandboxed), so Process.arguments is nil and your app crashes when you're doing Process.arguments[1] .

The solution is to use this in an actual application, not in a Playground.

Answer 2

You can use a custom "readLine()" function and a global input variable, each element in the input array is presenting a line:

import Foundation

var currentLine = 0
let input = ["5", "5 6 3"]

func readLine() -> String? {
    if currentLine < input.endIndex {
        let line = input[currentLine]
        currentLine += 1
        return line
    } else {
        return nil
    }
}

let firstLine = readLine() //  5
let secondLine = readLine() // 5 6 3
let thirdLine = readLine() // nil