什么是 String.Encoding.unicode？

Question

Swift 提供了一系列字符串编码。在我写这篇文章的时候，none of them are documented，这使得这比应该的更加混乱......

我能理解.ascii means it's ASCII encoded, .utf8 means the string is UTF-8 encoded, and .utf16BigEndian means the string is UTF-16 but big-endian。这些显然映射到真实的文本编码。

然后是.unicode. There is no "Unicode" encoding. The Unicode standard defines UTF-8, UTF-16, and UTF-32，正如我上面所说，已经在Swift中定义了。

算出最适合系统的那个是花哨的吗？它是 .utf8 的别名吗？是不是有些奇怪的 Apple Unicode 编码？

Answer 1

它似乎是 .utf16 的别名。来自 CFString.h:

#define kCFStringEncodingInvalidId (0xffffffffU)
typedef CF_ENUM(CFStringEncoding, CFStringBuiltInEncodings) {
    kCFStringEncodingMacRoman = 0,
    kCFStringEncodingWindowsLatin1 = 0x0500, /* ANSI codepage 1252 */
    kCFStringEncodingISOLatin1 = 0x0201, /* ISO 8859-1 */
    kCFStringEncodingNextStepLatin = 0x0B01, /* NextStep encoding*/
    kCFStringEncodingASCII = 0x0600, /* 0..127 (in creating CFString, values greater than 0x7F are treated as corresponding Unicode value) */
    kCFStringEncodingUnicode = 0x0100, /* kTextEncodingUnicodeDefault  + kTextEncodingDefaultFormat (aka kUnicode16BitFormat) */
    kCFStringEncodingUTF8 = 0x08000100, /* kTextEncodingUnicodeDefault + kUnicodeUTF8Format */
    kCFStringEncodingNonLossyASCII = 0x0BFF, /* 7bit Unicode variants used by Cocoa & Java */

    kCFStringEncodingUTF16 = 0x0100, /* kTextEncodingUnicodeDefault + kUnicodeUTF16Format (alias of kCFStringEncodingUnicode) */
    kCFStringEncodingUTF16BE = 0x10000100, /* kTextEncodingUnicodeDefault + kUnicodeUTF16BEFormat */
    kCFStringEncodingUTF16LE = 0x14000100, /* kTextEncodingUnicodeDefault + kUnicodeUTF16LEFormat */

    kCFStringEncodingUTF32 = 0x0c000100, /* kTextEncodingUnicodeDefault + kUnicodeUTF32Format */
    kCFStringEncodingUTF32BE = 0x18000100, /* kTextEncodingUnicodeDefault + kUnicodeUTF32BEFormat */
    kCFStringEncodingUTF32LE = 0x1c000100 /* kTextEncodingUnicodeDefault + kUnicodeUTF32LEFormat */
};

您可以通过以下方式确认：

print(String.Encoding.unicode.rawValue, String.Encoding.utf16.rawValue)

什么是 String.Encoding.unicode？

What is String.Encoding.unicode?

string

unicode

encoding

swift

swift-string