反向NSString文本

我一直在如何做到这一点，但我怎么会扭转一个NSString？ 例如：嗨将成为：呃

我正在寻找最简单的方法来做到这一点。

谢谢！

@Vince我做了这个方法：

- (IBAction)doneKeyboard { // first retrieve the text of textField1 NSString *myString = field1.text; NSMutableString *reversedString = [NSMutableString string]; NSUInteger charIndex = 0; while(myString && charIndex < [myString length]) { NSRange subStrRange = NSMakeRange(charIndex, 1); [reversedString appendString:[myString substringWithRange:subStrRange]]; charIndex++; } // reversedString is reversed, or empty if myString was nil field2.text = reversedString; } 

我把这个方法连接到textfield1的didendonexit。 当我点击完成button，它不会扭转文字，UILabel只显示我input的UITextField的文字。 哪里不对？

Answer 1

写一个简单的循环来做到这一点：

 // myString is "hi" NSMutableString *reversedString = [NSMutableString string]; NSInteger charIndex = [myString length]; while (charIndex > 0) { charIndex--; NSRange subStrRange = NSMakeRange(charIndex, 1); [reversedString appendString:[myString substringWithRange:subStrRange]]; } NSLog(@"%@", reversedString); // outputs "ih" 

在你的情况下：

 // first retrieve the text of textField1 NSString *myString = textField1.text; NSMutableString *reversedString = [NSMutableString string]; NSInteger charIndex = [myString length]; while (myString && charIndex > 0) { charIndex--; NSRange subStrRange = NSMakeRange(charIndex, 1); [reversedString appendString:[myString substringWithRange:subStrRange]]; } // reversedString is reversed, or empty if myString was nil textField2.text = reversedString; 

Answer 2

块版本。

 NSString *myString = @"abcdefghijklmnopqrstuvwxyz"; NSMutableString *reversedString = [NSMutableString stringWithCapacity:[myString length]]; [myString enumerateSubstringsInRange:NSMakeRange(0,[myString length]) options:(NSStringEnumerationReverse | NSStringEnumerationByComposedCharacterSequences) usingBlock:^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop) { [reversedString appendString:substring]; }]; // reversedString is now zyxwvutsrqponmlkjihgfedcba 

Answer 3

jano的回答是正确的。 不幸的是，它创造了很多不必要的临时对象。 这是一个更快（更复杂）的实现，基本上做同样的事情，但使用memcpy和unichar缓冲区来保持内存分配到最低限度。

 - (NSString *)reversedString { NSUInteger length = [self length]; if (length < 2) { return self; } unichar *characters = calloc(length, sizeof(unichar)); unichar *reversedCharacters = calloc(length, sizeof(unichar)); if (!characters || !reversedCharacters) { free(characters); free(reversedCharacters); return nil; } [self getCharacters:characters range:NSMakeRange(0, length)]; NSUInteger i = length - 1; NSUInteger copiedCharacterCount = 0; // Starting from the end of self, copy each composed character sequence into reversedCharacters while (copiedCharacterCount < length) { NSRange characterRange = [self rangeOfComposedCharacterSequenceAtIndex:i]; memcpy(reversedCharacters + copiedCharacterCount, characters + characterRange.location, characterRange.length * sizeof(unichar)); i = characterRange.location - 1; copiedCharacterCount += characterRange.length; } free(characters); NSString *reversedString = [[NSString alloc] initWithCharactersNoCopy:reversedCharacters length:length freeWhenDone:YES]; if (!reversedString) { free(reversedCharacters); } return reversedString; } 

我testing了这个长度在1到128之间的100,000个随机多字节Unicodestring。这个版本比jano的速度快了4-5倍。

 Enumerate substrings: 2.890528 MemCopy: 0.671090 Enumerate substrings: 2.840411 MemCopy: 0.662882 

testing代码在https://gist.github.com/prachigauriar/9739805 。

更新 ：我再次尝试通过简单地转换为UTF-32缓冲区，并扭转。

 - (NSString *)qlc_reversedStringWithUTF32Buffer { NSUInteger length = [self length]; if (length < 2) { return self; } NSStringEncoding encoding = NSHostByteOrder() == NS_BigEndian ? NSUTF32BigEndianStringEncoding : NSUTF32LittleEndianStringEncoding; NSUInteger utf32ByteCount = [self lengthOfBytesUsingEncoding:encoding]; uint32_t *characters = malloc(utf32ByteCount); if (!characters) { return nil; } [self getBytes:characters maxLength:utf32ByteCount usedLength:NULL encoding:encoding options:0 range:NSMakeRange(0, length) remainingRange:NULL]; NSUInteger utf32Length = utf32ByteCount / sizeof(uint32_t); NSUInteger halfwayPoint = utf32Length / 2; for (NSUInteger i = 0; i < halfwayPoint; ++i) { uint32_t character = characters[utf32Length - i - 1]; characters[utf32Length - i - 1] = characters[i]; characters[i] = character; } return [[NSString alloc] initWithBytesNoCopy:characters length:utf32ByteCount encoding:encoding freeWhenDone:YES]; } 

这比memcpy版本快大约3-4倍。 上述要点已经更新了最新版本的代码。

 Enumerate substrings: 2.168705 MemCopy: 0.488320 UTF-32: 0.150822 Enumerate substrings: 2.169655 MemCopy: 0.481786 UTF-32: 0.147534 Enumerate substrings: 2.248812 MemCopy: 0.505995 UTF-32: 0.154531 

Answer 4

我认为我会抛出另一个版本，以防万一有人感兴趣..个人而言，我喜欢使用NSMutableString更干净的方法，但如果性能是最高优先级，这是更快：

 - (NSString *)reverseString:(NSString *)input { NSUInteger len = [input length]; unichar *buffer = malloc(len * sizeof(unichar)); if (buffer == nil) return nil; // error! [input getCharacters:buffer]; // reverse string; only need to loop through first half for (NSUInteger stPos=0, endPos=len-1; stPos < len/2; stPos++, endPos--) { unichar temp = buffer[stPos]; buffer[stPos] = buffer[endPos]; buffer[endPos] = temp; } return [[NSString alloc] initWithCharactersNoCopy:buffer length:len freeWhenDone:YES]; } 

我也写了一个快速testing，以便将其与更传统的NSMutableString方法（我也在下面包括）进行比较：

 // test reversing a really large string NSMutableString *string = [NSMutableString new]; for (int i = 0; i < 10000000; i++) { int digit = i % 10; [string appendFormat:@"%d", digit]; } NSTimeInterval startTime = [[NSDate date] timeIntervalSince1970]; NSString *reverse = [self reverseString:string]; NSTimeInterval elapsedTime = [[NSDate date] timeIntervalSince1970] - startTime; NSLog(@"reversed in %f secs", elapsedTime); 

结果是：

• 使用NSMutableString方法（下面） – “在3.720631秒倒”

• 使用unichar *缓冲方法（上面） – “在0.032604秒内逆转”

仅供参考，以下是用于此比较的NSMutableString方法：

 - (NSString *)reverseString:(NSString *)input { NSUInteger len = [input length]; NSMutableString *result = [[NSMutableString alloc] initWithCapacity:len]; for (int i = len - 1; i >= 0; i--) { [result appendFormat:@"%c", [input characterAtIndex:i]]; } return result; } 

Answer 5

如果你只迭代一半string交换每个字符的末尾，会更快吗？ 所以对于一个5字符的string，你交换字符1 + 5，然后2 + 4和3不需要交换任何东西。

 NSMutableString *reversed = [original mutableCopyWithZone:NULL]; NSUInteger i, length; length = [reversed length]; for (i = 0; i < length / 2; i++) { // Store the first character as we're going to replace with the character at the end // in the example, it would store 'h' unichar startChar = [reversed characterAtIndex:i]; // Only make the end range once NSRange endRange = NSMakeRange(length - i, 1); // Replace the first character ('h') with the last character ('i') // so reversed now contains "ii" [reversed replaceCharactersInRange:NSMakeRange(i, 1) withString:[reversed subStringWithRange:endRange]; // Replace the last character ('i') with the stored first character ('h) // so reversed now contains "ih" [reversed replaceCharactersInRange:endRange withString:[NSString stringWithFormat:@"%c", startChar]]; } 

编辑—-

做了一些testing后，答案是否定的，比慢慢的慢6倍。 让我们放慢速度的是为replaceCharactersInRange：withString方法创build临时NSString。 这里是一个只通过直接操作字符数据来创build一个NSString的方法，在简单的testing中似乎要快得多。

 NSUInteger length = [string length]; unichar *data = malloc(sizeof (unichar) * length); int i; for (i = 0; i < length / 2; i++) { unichar startChar = [string characterAtIndex:i]; unichar endChar = [string characterAtIndex:(length - 1) - i]; data[i] = endChar; data[(length - 1) - i] = startChar; } NSString *reversed = [NSString stringWithCharacters:data length:length]; free(data); 

Answer 6

使用任何对象的方法：NSString，NSNumber等。：

 NSLog(@"%@",[self reverseObject:@12345]); NSLog(@"%@",[self reverseObject:@"Hello World"]); 

方法：

 -(NSString*)reverseObject:(id)string{ string = [NSString stringWithFormat:@"%@",string]; NSMutableString *endString = [NSMutableString new]; while ([string length]!=[endString length]) { NSRange range = NSMakeRange([string length]-[endString length]-1, 1); [endString appendString: [string substringWithRange:range]]; } return endString;} 

日志：

 2014-04-16 11:20:25.312 TEST[23733:60b] 54321 2014-04-16 11:20:25.313 TEST[23733:60b] dlroW olleH 

Answer 7

使用recursion来反转string：

 @implementation NSString (Reversed) + (NSString *)reversedStringFromString:(NSString *)string { NSUInteger count = [string length]; if (count <= 1) { // Base Case return string; } else { NSString *lastLetter = [string substringWithRange:NSMakeRange(count - 1, 1)]; NSString *butLastLetter = [string substringToIndex:count - 1]; return [lastLetter stringByAppendingString:[self reversedStringFromString:butLastLetter]]; } } @end 

Answer 8

没有一个答案似乎考虑多字节字符，所以这里是我的示例代码。 它假设你只能传递比一个字符长的string。

 - (void)testReverseString:(NSString *)string { NSMutableString *rString = [NSMutableString new]; NSInteger extractChar = [string length] - 1; while (extractChar >= 0) { NSRange oneCharPos = [string rangeOfComposedCharacterSequenceAtIndex:extractChar]; for (NSUInteger add = 0; add < oneCharPos.length; ++ add) { unichar oneChar = [string characterAtIndex:oneCharPos.location + add]; [rString appendFormat:@"%C", oneChar]; } extractChar -= oneCharPos.length; } NSLog(@"%@ becomes %@", string, encryptedString ); } 

Answer 9

• NSString到char utf32（总是32位（unsigned int））
• 相反
• 将utf32字符转换成NSString

---

 + (NSString *)reverseString3:(NSString *)str { unsigned int *cstr, buf, len = [str length], i; cstr = (unsigned int *)[str cStringUsingEncoding:NSUTF32LittleEndianStringEncoding]; for (i=0;i < len/2;i++) buf = cstr[i], cstr[i] = cstr[len -i-1], cstr[len-i-1] = buf; return [[NSString alloc] initWithBytesNoCopy:cstr length:len*4 encoding:NSUTF32LittleEndianStringEncoding freeWhenDone:NO]; } 

例如：Apple_is—>si_elppA

Answer 10

 NSMutableString *result = [NSMutableString stringWithString:@""]; for (long i = self.length - 1; i >= 0; i--) { [result appendFormat:@"%c", [self characterAtIndex:i]]; } return (NSString *)result; 

Answer 11

Swift 2.0：

1）let str =“你好，世界！” 让reverse = String（str.characters.reverse（））打印（反转）

简而言之：

 String("This is a test string.".characters.reverse()) 

2）

 let string = "This is a test string." let characters = string.characters let reversedCharacters = characters.reverse() let reversedString = String(reversedCharacters) 

简而言之：

 String("This is a test string.".characters.reverse()) 

要么

 let string = "This is a test string." let array = Array(string) let reversedArray = array.reverse() let reversedString = String(reversedArray) The short way : String(Array("This is a test string.").reverse()) 

在游戏场地testing：

 import Cocoa //Assigning a value to a String variable var str = "Hello, playground" //Create empty character Array. var strArray:Character[] = Character[]() //Loop through each character in the String for character in str { //Insert the character in the Array variable. strArray.append(character) } //Create a empty string var reversedStr:String = "" //Read the array from backwards to get the characters for var index = strArray.count - 1; index >= 0;--index { //Concatenate character to String. reversedStr += strArray[index] } 

较短的版本：

 var str = “Hello, playground” var reverseStr = “” for character in str { reverseStr = character + reverseStr } 

Answer 12

Google是你的朋友 ：

 -(NSString *) reverseString { NSMutableString *reversedStr; int len = [self length]; // Auto released string reversedStr = [NSMutableString stringWithCapacity:len]; // Probably woefully inefficient... while (len > 0) [reversedStr appendString: [NSString stringWithFormat:@"%C", [self characterAtIndex:--len]]]; return reversedStr; } 

Answer 13

以下是Objective-C中的一组类别，它们将反转NSStrings和NSAttributedStrings（同时保留字符属性）： TextFlipKit

例如：

 NSString *example = @"Example Text"; NSString *reversed = example.tfk_reversed; NSLog(@"Reversed: %@", reversed); //prints 'Reversed: txeT elpmaxE' 

Answer 14

迅速：

 let string = "reverse" let reversedStringCollection = string.characters.reversed() for character in reversedStringCollection { reversedString.append(character) print(reversedString) } 

Answer 15

将一个类别添加到NSString中，以便将来可以在任何NSString上调用reverse：

 #import "NSString+Reverse.h" @implementation NSString (Reverse) -(NSString*)reverse { char* cstring = (char*)[self UTF8String]; int length = [self length]-1; int i=0; while (i<=length) { unichar tmp = cstring[i]; cstring[i] = cstring[length]; cstring[length] = tmp; i++; length--; } return [NSString stringWithCString:cstring encoding:NSUTF8StringEncoding]; } @end 

Answer 16

 str=@"india is my countery"; array1=[[NSMutableArray alloc] init]; for(int i =0 ;i<[str length]; i++) { NSString *singleCharacter = [NSString stringWithFormat:@"%c", [str characterAtIndex:i]]; [array1 addObject:singleCharacter]; } NSMutableString* theString = [NSMutableString string]; for (int i=[array1 count]-1; i>=0;i--){ [theString appendFormat:@"%@",[array1 objectAtIndex:i]]; } 

Answer 17

我写了一个类别：D

//NSString+Reversed.h #import

 // // NSString+Reversed.h // HTMLPageFormatter // Created by beit46 on 21.06.13. // @interface NSString (Reversed) - (NSString *)reversedString; @end 

//NSString+Reversed.m

 // // NSString+Reversed.m // HTMLPageFormatter // Created by beit46 on 21.06.13. #import "NSString+Reversed.h" @implementation NSString (Reversed) - (NSString *)reversedString { NSMutableString *reversedString = [NSMutableString stringWithCapacity:[self length]]; [self enumerateSubstringsInRange:NSMakeRange(0,[self length]) options:(NSStringEnumerationReverse | NSStringEnumerationByComposedCharacterSequences) usingBlock:^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop) { [reversedString appendString:substring]; }]; return [reversedString copy]; } @end 

Answer 18

我有两个简单的解决scheme：

 +(NSString*)reverseString:(NSString *)str { NSMutableString* reversed = [NSMutableString stringWithCapacity:str.length]; for (int i = (int)str.length-1; i >= 0; i--){ [reversed appendFormat:@"%c", [str characterAtIndex:i]]; } return reversed; } +(NSString*)reverseString2:(NSString *)str { char* cstr = (char*)[str UTF8String]; int len = (int)str.length; for (int i = 0; i < len/2; i++) { char buf = cstr[i]; cstr[i] = cstr[len-i-1]; cstr[len-i-1] = buf; } return [[NSString alloc] initWithBytes:cstr length:len encoding:NSUTF8StringEncoding]; } 

现在，让我们testing一下！

 NSString* str = @"Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language"; NSLog(@"REV 1: %@", [Util reverseString:str]); start = [NSDate date]; for (int i = 0 ; i < 1000; ++i) [Util reverseString:str]; end = [NSDate date]; NSLog(@"Time per 1000 repeats: %f", [end timeIntervalSinceDate:start]); NSLog(@"REV 2: %@", [Util reverseString2:str]); start = [NSDate date]; for (int i = 0 ; i < 1000; ++i) [Util reverseString2:str]; end = [NSDate date]; NSLog(@"Time per 1000 repeats: %f", [end timeIntervalSinceDate:start]); 

结果：

 ConsoleTestProject[68292:303] REV 1: egaugnal gnimmargorp C eht ot gnigassem elyts-klatllamS sdda taht egaugnal gnimmargorp detneiro-tcejbo ,esoprup-lareneg a si C-evitcejbO ConsoleTestProject[68292:303] Time per 1000 repeats: 0.063880 ConsoleTestProject[68292:303] REV 2: egaugnal gnimmargorp C eht ot gnigassem elyts-klatllamS sdda taht egaugnal gnimmargorp detneiro-tcejbo ,esoprup-lareneg a si C-evitcejbO ConsoleTestProject[68292:303] Time per 1000 repeats: 0.002038 

而更多的字符结果是：

 ConsoleTestProject[68322:303] chars: 1982 ConsoleTestProject[68322:303] Time 1 per 1000 repeats: 1.014893 ConsoleTestProject[68322:303] Time 2 per 1000 repeats: 0.024928 

与上述function相同的文字：

 ConsoleTestProject[68366:303] Time 1 per 1000 repeats: 0.873574 ConsoleTestProject[68366:303] Time 2 per 1000 repeats: 0.019300 ConsoleTestProject[68366:303] Time 3 per 1000 repeats: 0.342735 <-Vladimir Gritsenko ConsoleTestProject[68366:303] Time 4 per 1000 repeats: 0.584012 <- Jano 

所以，select性能！

Answer 19

 -(NSString *) reverseString: (NSString *) string { NSMutableArray *letters = [[NSMutableArray alloc] init]; for (int i=0; i<[string length]; i++) [letters addObject: [string substringWithRange: NSMakeRange(i, 1)]]; NSArray *reversed = [[letters reverseObjectEnumerator] allObjects]; return [reversed componentsJoinedByString: @""]; }