NSString Reverse Text

Question

I understand so much about how to do this, but how would I turn NSString? Example: hi would become: ih

I am looking for the easiest way to do this.

Thank!

@Vince I made this method:

- (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; } 

I hooked this method to textfield1 didendonexit. When I click Finish, it does not cancel the text, UILabel just shows the text of the UITextField that I entered. What's wrong?

Answer 1

Write a simple loop for this:

 // 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" 

In your case:

 // 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

Block version.

 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

Janos answer is correct. Unfortunately, it creates a lot of unnecessary temporary objects. Here is a much faster (more complicated) implementation that basically does the same thing, but uses memcpy and unichar buffers to minimize memory allocations.

 - (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; } 

I tested this on 100,000 random Unicode multibyte strings with lengths from 1 to 128. This version is about 4-5 times faster than janos.

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

The test code is at https://gist.github.com/prachigauriar/9739805 .

Update . I tried this again by simply translating it into the UTF-32 buffer and changing it.

 - (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]; } 

This is about 3-4 times faster than the memcpy version. The above text has been updated with the latest code.

 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

It seemed to me that I would choose a different version there, if someone is interested. Personally, I like the cleaner approach using NSMutableString, but if performance is the highest priority, it's faster:

 - (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]; } 

I also wrote a quick test to compare it with the more traditional NSMutableString method (which I also included below):

 // 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); 

Results:

• using the NSMutableString method (below) - "canceled in 3.720631 sec"

• using the unichar * buffer method (above) - "canceled in 0.032604 sec"

For reference, the NSMutableString method is used here for this comparison:

 - (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

Would it be faster if you only repeated more than half the line, replacing the characters at each end? So, for a line with 5 characters you change the characters 1 + 5, then 2 + 4 and 3 do not need to be replaced.

 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]]; } 

edit ----

After doing some tests, the answer is "No", about 6 times slower than the version that iterates over everything. The thing that slows us down is creating temporary NSStrings for the replaceCharactersInRange: withString method. Here is a method that creates only one NSString, manipulating character data directly and in simple tests much faster.

 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

Use the method with any objects: NSString, NSNumber, etc .:

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

Method:

 -(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;} 

Log:

 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

Cancel the line using recursion:

 @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

None of the answers deal with multibyte characters, so here is a sample code. It is assumed that you only ever go in a string longer than one character.

 - (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 in char utf32 (always 32 bits (unsigned int))
• Back
• char utf32 in 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]; } 

Example: 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 = "Hello world!" let reverseed = String (str.characters.reverse ()) print (in reverse order)

In short:

 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) 

Shortcut:

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

OR

 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()) 

Tested on the playground:

 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] } 

Shorter version:

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

Answer 12

Google is your friend :

 -(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

Here is a set of categories in Objective-C that will override both NSStrings and NSAttributedStrings (while preserving character attributes): TextFlipKit

For example:

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

Answer 14

Swift:

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

Answer 15

Add a category to NSString so that in the future you can call a callback for any NSString as follows:

 #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

I wrote an ove category that one: 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

I have two simple solutions for this purpose:

 +(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]; } 

Now let's test it!

 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]); 

Results:

 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 

And the result was:

 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 

The same text with the above functions:

 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 

So, choose your performance!

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: @""]; }