UnsafePointer< Uint8>的问题在Swift的SQLite项目中 [英] Issue with UnsafePointer<Uint8> in SQLite project in Swift

问题描述

我们正在使用Swift在iOS中实现SQLite，而不使用包装器或Objective-C桥接。一切正常，除了在进行查询和提取结果时。问题在于从Swite中的SQLite返回的 UnsafePointer< UInt8> ，如下所示：

We are implementing SQLite in iOS, in Swift, without using wrappers or Objective-C bridging. Everything works fine, except when doing a query and extracting the result. The issue is with the UnsafePointer<UInt8> that is returned from SQLite in Swift as follows:

var querySQL = "SELECT address, phone FROM CONTACTS WHERE NAME = 'myName'"
var cQuery = querySQL.cStringUsingEncoding(NSUTF8StringEncoding)
var statement: COpaquePointer = nil
if sqlite3_prepare_v2(contactsDB, cQuery!, -1, &statement, nil) == SQLITE_OK {
   if sqlite3_step(statement) == SQLITE_ROW {
   var address : UnsafePointer<UInt8> = sqlite3_column_text(statement, 0)
   var data = NSData(bytes: address, length: 10)
   var string = NSString(data: data, encoding: NSUTF8StringEncoding)
   println(string)

正如您所看到的，如果我们知道对象的长度，我们可以将指针转换为String（在这个案例10）

As you can see, we can convert the pointer to String if we know the length of the object (in this case 10)

为了深入研究这个问题，我有以下例子

To dig into this issue, I have the following example

let pointerFromString: UnsafePointer<Int8> = "xyz".cStringUsingEncoding(NSUTF8StringEncoding)
let stringFromPointer = String.fromCString(anotherPointerFromString_Int8)                    println(stringFromPointer!)

鉴于 CChar 是 Int8 的别名，我可以转换 String to UnsafePointer< Int8> 使用 .cStringUsingEncoding（），然后返回 String 使用 .fromCString（< UnsafePointer_CChar>）

Given that CChar is an alias of Int8, I can convert a String to UnsafePointer<Int8> using .cStringUsingEncoding(), and then back to String using .fromCString(<UnsafePointer_CChar>)

问题是我的SQLite结果是 UnsafePointer_UInt8 ，它不能用于 .fromCString（）

The problem is that my SQLite result is a UnsafePointer_UInt8, that can´t be used with .fromCString()

底线问题是：是否可以将 UnsafePointer_UInt8 转换或转换为 UnsafePointer_Int8

The bottom line question is: Is it possible to convert or cast a UnsafePointer_UInt8 to UnsafePointer_Int8

推荐答案

这应该有效：

let address = sqlite3_column_text(statement, 0)
let string = String.fromCString(UnsafePointer<CChar>(address))

Swift 3更新（Xcode 8），比较 Swift 3：转换以null结尾的UnsafePointer< UINT8>到字符串：

let string = String(cString: sqlite3_column_text(statement, 0))

这篇关于UnsafePointer&lt; Uint8&gt;的问题在Swift的SQLite项目中的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！