[英]Converting array of C strings to Swift string array
In Swift 3, C function with signature const char *f()
is mapped to UnsafePointer<Int8>! f()
在Swift 3中,带有签名const char *f()
C函数被映射到UnsafePointer<Int8>! f()
UnsafePointer<Int8>! f()
on import. UnsafePointer<Int8>! f()
关于进口。 It's result can be converted to a Swift string as: 它的结果可以转换为Swift字符串:
let swiftString = String(cString: f())
The question is, how a NULL terminated C array of C strings can be mapped to Swift array of strings? 问题是,如何将NULL终止的C字符串C字符串映射到Swift字符串数组?
The original C signature: 原始C签名:
const char **f()
Imported Swift signature: 导入的Swift签名:
UnsafeMutablePointer<UnsafePointer<Int8>?>! f()
Swift array of strings: Swift数组字符串:
let stringArray: [String] = ???
There is no built-in method as far as I know. 据我所知,没有内置方法。 You have to iterate over the returned pointer array, converting C strings to Swift String
s, until a nil
pointer is found: 你必须遍历返回的指针数组,将C字符串转换为Swift String
,直到找到一个nil
指针:
if var ptr = f() {
var strings: [String] = []
while let s = ptr.pointee {
strings.append(String(cString: s))
ptr += 1
}
// Now p.pointee == nil.
print(strings)
}
Remark: Swift 3 uses optional pointers for pointers that can be nil
. 备注: Swift 3使用可选指针作为nil
指针。 In your case, f()
returns an implicitly unwrapped optional because the header file is not "audited": The compiler does not know whether the function can return NULL
or not. 在您的情况下, f()
返回一个隐式解包的可选项,因为头文件未被“审计”:编译器不知道该函数是否可以返回NULL
。
Using the "nullability annotations" you can provide that information to the Swift compiler: 使用“nullability annotations”,您可以将该信息提供给Swift编译器:
const char * _Nullable * _Nullable f(void);
// Imported to Swift as
public func f() -> UnsafeMutablePointer<UnsafePointer<Int8>?>?
if the function can return NULL
, and 如果函数可以返回NULL
,和
const char * _Nullable * _Nonnull f(void);
// Imported to Swift as
public func f() -> UnsafeMutablePointer<UnsafePointer<Int8>?>
if f()
is guaranteed to return a non-NULL result. 如果f()
保证返回非NULL结果。
For more information about the nullability annotations, see for example Nullability and Objective-C in the Swift blog. 有关可空性注释的更多信息,请参阅Swift博客中的Nullability和Objective-C 。
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