将Objective-C方法转换为Swift for NSInputStream（将字节转换为double） [英] Convert an Objective-C method into Swift for NSInputStream (convert bytes into double)

问题描述

我在Objective-C中有以下代码：

I have the following code in Objective-C:

- (double)readDouble
{
    double value = 0.0;

    if ([self read:(uint8_t *)&value maxLength:8] != 8)
    {
        NSLog(@"***** Couldn't read double");
    }

    return value;
}

它有效。但我不知道如何将其转换为Swift。这是我的代码：

It works. But I don't know how to convert it to Swift. Here is my code:

public func readDouble() -> Double {

    var value : Double = 0.0

    var num = self.read((uint8_t *)&value, maxLength:8) // got compiling error here!
    if num != 8 {

    }
}

错误信息是：

无法使用类型'的参数列表调用'&'（$ T4，maxLength：
IntegerLiteralConvertible）'

Cannot invoke '&' with an argument list of type '($T4, maxLength: IntegerLiteralConvertible)'

有人可以帮忙吗？谢谢

我正在使用的测试数据（1.25）：

The testing data I'm using (1.25):

14 AE 47 E1 7A 14 F4 3F

更新：

一个简单的c解决方案，但是如何在Swift中执行此操作？

A simple c solution, but how to do this in Swift?

double d = 0;
unsigned char buf[sizeof d] = {0};

memcpy(&d, buf, sizeof d);

推荐答案

这应该有效：

let num = withUnsafeMutablePointer(&value) {
    self.read(UnsafeMutablePointer($0), maxLength: sizeofValue(value))
}

解释： withUnsafeMutablePointer（）使用设置为地址的唯一参数
（ $ 0 ，以简写表示法）调用闭包（块）值。

Explanation: withUnsafeMutablePointer() calls the closure (block) with the only argument ($0 in shorthand notation) set to the address of value.

$ 0 的类型为 UnsafeMutablePointer< Double> 和 read（）期望
UnsafeMutablePointer< UInt8> 作为第一个参数，因此另一个转换
是必要的。然后将闭包的返回值分配给 num 。

$0 has the type UnsafeMutablePointer<Double> and read() expects an UnsafeMutablePointer<UInt8> as the first argument, therefore another conversion is necessary. The return value of the closure is then assigned to num.

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