深入理解蘋果系統（Unicode）字串的排序方法

Localized string comparisons are based on the Unicode Collation Algorithm, as tailored for different languages by CLDR (Common Locale Data Repository). Both are projects of the Unicode Consortium. Unicode is a registered trademark of Unicode, Inc.

Collation is the general term for the process and function of determining the sorting order of strings of characters.

NSArray *rawArray = @[@"愛你", @"一生一世",@"㊀", @"上",@"㊤",@"μ",@"язык",@"..",@"123",@"@",@"AA",@"abc",@"abb"];
//1. 預設排序方式
NSArray *defaultedSortedArray = [rawArray sortedArrayUsingComparator:^NSComparisonResult(id_Nonnull obj1, id_Nonnull obj2) {
return [obj1 compare:obj2 options:NSCaseInsensitiveSearch];
}];
__block NSMutableArray *codeUnits = [NSMutableArray array];
[defaultedSortedArray enumerateObjectsUsingBlock:^(NSString*_Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
[codeUnits addObject:@([obj characterAtIndex:0])];
}];
NSLog(@"預設Unicode碼點值排序 %@ 對應的各個字串的首字元碼點值是 %@", [defaultedSortedArray descriptionWithLocale:cnLocal], codeUnits);

排序結果 
 ..123@AAabbabcμязык㊀㊤一生一世上愛你 
 對應的各個字串的首字元碼點值是 
 46496465979795611031292812964199681997829233

0000; [.0000.0000.0000] # <NULL>
0001; [.0000.0000.0000] # <START OF HEADING>
0002; [.0000.0000.0000] # <START OF TEXT>
0003; [.0000.0000.0000] # <END OF TEXT>

NSLocale *enLocale = [[NSLocale alloc] initWithLocaleIdentifier:@"en"];
defaultedSortedArray = [rawArray sortedArrayUsingComparator:^NSComparisonResult(NSString*_Nonnull obj1, NSString*_Nonnull obj2) {
return [obj1 compare:obj2 options:0 range:NSMakeRange(0, obj1.length) locale:enLocale];
}];
NSLog(@"預設排序規則或者指定地區為locale後的排序結果是 %@", [defaultedSortedArray descriptionWithLocale:cnLocal]);

預設排序規則或者指定地區為en後的排序結果是 
 ..（ch(en@123AAabbabcμязык㊀一生一世上㊤愛你

預設排序規則或者指定地區為zh_CN後的排序結果是 
 ..（ch(en@0124123艾你愛你産上㊤㊀一生一世重逢重要aaAAabbμязык 
 
 預設排序規則或者指定地區為ru_CN後的排序結果是 
 ..（ch(en@0124123языкaaAAabbμ㊀一生一世上㊤愛你産艾你重要重逢

public func localizedStandardCompare(_ string: String) -> ComparisonResult {
return compare(string, options: [.caseInsensitive, .numeric, .widthInsensitive, .forcedOrdering], range: NSRange(location: 0, length: length), locale: Locale.current._bridgeToObjectiveC())
}

NSCaseInsensitiveSearch//大小寫不敏感
NSNumericSearch //對字串中出現的數字字元進行數字化的大小比較，比如Foo2.txt < Foo7.txt < Foo25.txt
NSWidthInsensitiveSearch //忽略寬度，按照實際表示的意思來對比，如'a' = UFF41
NSForcedOrderingSearch //強制返回Ascending或者Descending，和NSCaseInsensitiveSearch結合起來就是例如"aaa" > "AAA"

if (numerically && ((0 == strBuf1Len) && (str1Char <= '9') && (str1Char >= '0')) && ((0 == strBuf2Len) && (str2Char <= '9') && (str2Char >= '0'))) { // If both are not ASCII digits, then don't do numerical comparison here
uint64_t intValue1 = 0, intValue2 = 0;// !!! Doesn't work if numbers are > max uint64_t
CFIndex str1NumRangeIndex = str1Index;
CFIndex str2NumRangeIndex = str2Index;

do {
intValue1 = (intValue1 * 10) + (str1Char - '0');
str1Char = CFStringGetCharacterFromInlineBuffer(&inlineBuf1, ++str1Index);
} while ((str1Char <= '9') && (str1Char >= '0'));

do {
intValue2 = intValue2 * 10 + (str2Char - '0');
str2Char = CFStringGetCharacterFromInlineBuffer(&inlineBuf2, ++str2Index);
} while ((str2Char <= '9') && (str2Char >= '0'));

if (intValue1 == intValue2) {
if (forceOrdering && (kCFCompareEqualTo == compareResult) && ((str1Index - str1NumRangeIndex) != (str2Index - str2NumRangeIndex))) {
compareResult = (((str1Index - str1NumRangeIndex) < (str2Index - str2NumRangeIndex)) ? kCFCompareLessThan : kCFCompareGreaterThan);
numericEquivalence = true;
forcedIndex1 = str1NumRangeIndex;
forcedIndex2 = str2NumRangeIndex;
}

continue;
} else if (intValue1 < intValue2) {
if (freeLocale && locale) {
CFRelease(locale);
}
return kCFCompareLessThan;
} else {
if (freeLocale && locale) {
CFRelease(locale);
}
return kCFCompareGreaterThan;
}
}