IBM Swift Sandbox無法解析對CoreFoundation函數的調用

Question

我正忙於IBM Swift沙箱的測試版;有沒有人知道爲什麼我得到下面的代碼的以下錯誤？：

LLVM錯誤：程序使用的外部函數CFAbsoluteTimeGetCurrent'無法解決！

// A demonstration of both iterative and recursive algorithms for computing the Fibonacci numbers. 

import CoreFoundation 

// A recursive algorithm to compute the Fibonacci numbers. 
func fibRec (n : Int) -> Double { 
    return (Double)(n < 3 ? 1 : fibRec(n - 1) + fibRec(n - 2)) 
} 

// An iterative algorithm to compute the Fibonacci numbers. 
func fibIter (n : Int) -> Double { 
    var f2 = 0.0 
    var f1 = 1.0 
    var f0 = 1.0 

    for _ in 0 ..< n { 
     f2 = f1 + f0 
     f0 = f1 
     f1 = f2 
    } 
    return f0 
} 

// Initialise array to hold algorithm execution times. 
var fibTimes = [Double]() 

// i is the ith Fibonacci number to be computed. 
for i in 120..<129 { 

    var fibNum = 0.0 
    var fibSum = 0.0 

    // j is the number of times to compute F(i) to obtain average. 
    for j in 0..<5 { 

     // Set start time. 
     let startTime = CFAbsoluteTimeGetCurrent() 

     // Uses the recursive algorithm. 
     //    fibNum = fibRec(i) 

     // Uses the iterative algorithm. 
     fibNum = fibIter(i) 
     fibTimes.insert(CFAbsoluteTimeGetCurrent() - startTime, atIndex: j) 
    } 

    // Compute the average execution time. 
    for p in fibTimes { 
     fibSum += p 
    } 
    fibSum = fibSum/5 

    print("Fibonacci number \(i) is: \(fibNum)") 
    print("Execution time:   \(fibSum) seconds") 
} 

Answer 1

你只需要import Foundation以及。

我不知道爲什麼需要這樣做（我希望有人知道，可以對此有所瞭解），但它是有效的。

Answer 2

要澄清，你必須導入他們兩個。

import Foundation 
import CoreFoundation 

另外，Glibc有clock（），它返回一個Int代替。例如：

import Glibc 
struct StartTimer { 
    let start = clock() 
    var elapsed = -1 
    mutating func stop() { elapsed = clock() - start } 
} 

var timer = StartTimer() 
/* do your work */ 
timer.stop() 
print("Elapsed Time: \(timer.elapsed)")