引用於GitHub：https://github.com/xiaoxiaocainiao/HostToIP/blob/master/HostToIP/ViewController.swift
這裡又根據自己需要做了少許改動，在此感謝下作者的無私提供。

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        getIPAddress("www.baidu.com")
    }

    override
 
 func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    // 域名解析
    func getIPAddress(domainName: String) -> String {
    var result = ""
        let host = CFHostCreateWithName(nil,domainName as CFString).takeRetainedValue()
        CFHostStartInfoResolution(host, .addresses, nil)
        var
 
 success: DarwinBoolean = false
        if let addresses = CFHostGetAddressing(host, &success)?.takeUnretainedValue() as NSArray?,
            let theAddress = addresses.firstObject as? NSData {
            var hostname = [CChar](repeating: 0, count: Int(NI_MAXHOST))
            if getnameinfo(theAddress.bytes.assumingMemoryBound(to: sockaddr.self), socklen_t(theAddress.length),
                           &hostname, socklen_t(hostname.count), nil, 0
 
, NI_NUMERICHOST) == 0 {
                let numAddress = String(cString: hostname)
                result = numAddress
                print(numAddress)
            }
        }
        return result
    }

}