swift - 在Swift 3(libxml2)中将字符串转换为UnsafePointer <xmlChar>的快捷方法

我正在为libxml2 C库开发一个Swift 3包装器。

有两种方便的方法可以将String转换为UnsafePointer<xmlChar>，反之亦然。在libxml2中，xmlChar声明为unsigned char。

UnsafePointer<xmlChar>到String并不复杂

func stringFrom(xmlchar: UnsafePointer<xmlChar>) -> String {
    let string = xmlchar.withMemoryRebound(to: CChar.self, capacity: 1) {
        return String(validatingUTF8: $0)
    }
    return string ?? ""
}

对于String到UnsafePointer<xmlChar>，我尝试了很多事情，例如

let bytes = string.utf8CString.map{ xmlChar($0) }
return UnsafePointer<xmlChar>(bytes)

但这是行不通的，我发现的唯一可行的解​​决方案是

func xmlCharFrom(string: String) -> UnsafePointer<xmlChar> {
    let pointer = (string as NSString).utf8String
    return unsafeBitCast(pointer, to: UnsafePointer<xmlChar>.self)
}

如果没有将桥梁转换为NSString和unsafeBitCast的方法，是否有更好，更快捷的方法？

最佳答案

我能想到的最快方法是只使用bitPattern:初始化程序:
let xmlstr = str.utf8CString.map { xmlChar(bitPattern: $0) }
这将为您提供Array的xmlChar。卡在上面，当您需要将Array传递给某些东西时，请使用withUnsafeBufferPointer的UnsafePointer方法:
xmlstr.withUnsafeBufferPointer { someAPIThatWantsAPointer($0.baseAddress!) }
不要让UnsafePointer从闭包中逸出，因为它在外面不合法。

编辑:这是如何妥协的？与其让函数返回指针，不如让它闭包。

func withXmlString<T>(from string: String, handler: (UnsafePointer<xmlChar>) throws -> T) rethrows -> T {
    let xmlstr = string.utf8CString.map { xmlChar(bitPattern: $0) }

    return try xmlstr.withUnsafeBufferPointer { try handler($0.baseAddress!) }
}

或者，作为String的扩展:

extension String {
    func withXmlString<T>(handler: (UnsafePointer<xmlChar>) throws -> T) rethrows -> T {
        let xmlstr = self.utf8CString.map { xmlChar(bitPattern: $0) }

        return try xmlstr.withUnsafeBufferPointer { try handler($0.baseAddress!) }
    }
}

关于swift - 在Swift 3(libxml2)中将字符串转换为UnsafePointer <xmlChar>的快捷方法，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/45965523/