如何在Swift中将Int32写入NSOutputStream

问题描述：

我正在尝试在Swift中将Int32写入NSOutputStream，但遇到了困难.在ObjC中，我会做这样的事情:

I'm trying to write an Int32 to an NSOutputStream in Swift and I'm having difficulties. In ObjC, I would have done something like this:

-(void)write4ByteField:(int32_t)value {
    [stream write:((value >> 24) & 0xff)];
    [stream write:((value >> 16) & 0xff)];
    [stream write:((value >> 8) & 0xff)];
    [stream write:(value & 0xff)];
}

但是，在Swift中，我真的不喜欢我做所有的低级位移位操作，而我放弃了在所有位置上强制转换值.

However, in Swift, it really doesn't like me doing all of that low-level bit-shifting and I gave up on casting the values all over the place.

我尝试过类似的事情:

func write4ByteField(value: Int32) {
    stream.write(&value, maxLength: sizeof(Int32))
}

但出现错误int16 is not convertible to @lvalue inout $T4

类似地，如果我尝试转到NSData，则会收到相同的错误:

Similarly, if I try to go to NSData I get the same error:

func write4ByteField(value: Int32) {
    let data = NSData(bytes: &value, length: sizeof(Int32)
    stream.write(data.bytes, maxLength: sizeof(Int32))
}

有什么建议吗?我猜我只是在以错误的方式来做.

Any suggestions? I'm guessing I am just going about this the wrong way.

答

您的最后一种方法几乎是正确的. value必须是一个变量参数这样您就可以将其用作输入输出表达式" &value，并且data.bytes需要强制转换:

Your last approach is almost correct. value needs to be a variable parameter so that you can use it as "in-out expression" &value, and data.bytes needs a cast:

func write4ByteField(var value: Int32) {
    let data = NSData(bytes: &value, length: sizeof(Int32))
    stream.write(UnsafePointer(data.bytes), maxLength: sizeof(Int32))
}

也可以在没有NSData的情况下完成，包括转换为big-endian 字节顺序:

It can also be done without NSData, including the conversion to big-endian byte order:

func write4ByteField(value: Int32) {
    var valueBE = value.bigEndian
    withUnsafePointer(&valueBE) { 
        self.stream.write(UnsafePointer($0), maxLength: sizeofValue(valueBE))
    }
}

如何在Swift中将Int32写入NSOutputStream

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