小编Jer*_* Xu的帖子

我的代码中没有调用didOutputSampleBuffer函数.我不知道为什么会这样.这是代码:

import UIKit
import AVFoundation
import Accelerate

class ViewController: UIViewController {

var captureSession: AVCaptureSession?
var dataOutput: AVCaptureVideoDataOutput?
var customPreviewLayer: AVCaptureVideoPreviewLayer?

@IBOutlet weak var camView: UIView!

override func viewWillAppear(animated: Bool) {
    super.viewDidAppear(animated)
    captureSession?.startRunning()
    //setupCameraSession()
}

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
    //captureSession?.startRunning()
    setupCameraSession()
}

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

func setupCameraSession() {
    // Session
    self.captureSession = AVCaptureSession()
    captureSession!.sessionPreset = …

在我的计算机上，long最大值为9223372036854775807。但是，当我unsigned long对较大的值感到厌倦时，编译器会发出警告，指出需要将其解释为unsigned long已经定义了该值。为什么会这样？

//assigning maximum value of a long integer. (No error)
long max_l = 9223372036854775807L;

//assigning an unsigned long integer.
unsigned long max_ul = 9223372036854775808L; //warning: integer literal is too large to be represented in a signed
                                             //integer type, interpreting as unsigned [-Wimplicitly-unsigned-literal]

cc --version
Apple LLVM version 10.0.1 (clang-1001.0.46.4)