我一直在谷歌搜索如何做到这一点，但我将如何扭转NSString？例如：你好了：ih
我正在寻找最简单的方法。
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。当我单击完成按钮时，它不会反转文本，UILabel只显示我输入的UITextField文本。有什么问题？
答案 0 :(得分：103)
阻止版本。
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
答案 1 :(得分：51)
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"
在您的情况下：
// 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;
答案 2 :(得分：10)
jano的回答是正确的。不幸的是，它会产生许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缓冲区将内存分配保持在最低限度。
- (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;
}
我在100,000个随机多字节Unicode字符串上测试了这个，长度在1到128之间。这个版本比jano快了4-5倍。
Enumerate substrings: 2.890528
MemCopy: 0.671090
Enumerate substrings: 2.840411
MemCopy: 0.662882
测试代码位于https://gist.github.com/prachigauriar/9739805。
更新：我只需转换为UTF-32缓冲区并将其反转即可再次尝试此操作。
- (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3-4倍。上述要点已使用最新版本的代码进行了更新。
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
答案 3 :(得分：8)
我想我会抛出另一个版本以防万一有兴趣..个人而言，我喜欢使用NSMutableString的更干净的方法，但如果性能是最高优先级，那么这个更快：
- (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];
}
我还写了一个快速测试，将它与更传统的NSMutableString方法（我在下面也包括在内）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（如下） - ＆＃34;在3.720631秒内反转＆＃34;
使用unichar *缓冲方法（上图） - ＆＃34;在0.032604秒内反转＆＃34;
仅供参考，这里是用于此比较的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;
}
答案 4 :(得分：3)
对任何对象使用方法：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
答案 5 :(得分：2)
如果你只迭代超过一半的字符串交换两端的字符会更快吗？因此，对于5个字符的字符串，您可以交换字符1 + 5，然后2 + 4和3不需要与任何东西交换。
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----
完成了一些测试后，答案是“否”，它比循环所有内容的版本慢约6倍。减慢我们速度的事情是为replaceCharactersInRange：withString方法创建临时NSStrings。这是一种通过直接操作字符数据只创建一个NSString的方法，在简单测试中似乎要快得多。
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);
答案 6 :(得分：2)
Swift 2.0：
1）让str =＆＃34;你好，世界！＆＃34; let reversed = 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)
简短的方法：
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())
在Play Ground上测试：
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
}
答案 7 :(得分：1)
使用递归反转字符串：
@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
答案 8 :(得分：1)
这些答案似乎都没有考虑多字节字符，所以这里是我的示例代码。它假设你只传入一个长于一个字符的字符串。
- (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 );
}
答案 9 :(得分：1)
+ (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];
}
示例：Apple_is---＆gt; si_elppA
答案 10 :(得分：1)
NSMutableString *result = [NSMutableString stringWithString:@""];
for (long i = self.length - 1; i >= 0; i--) {
[result appendFormat:@"%c", [self characterAtIndex:i]];
}
return (NSString *)result;
答案 11 :(得分：0)
我们也可以按如下方式实现反向字符串。
NSString *originalString = @"Hello";
NSString *reverseString;
for (NSUInteger index = originalString.length; index > 0; index--) {
char character = [originalString characterAtIndex:index];
reverseString = [reverseString stringByAppendingString:[NSString stringWithFormat:@"%c", character]];
}
或
NSString *originalString = @"Hello";
NSString *reverseString;
for (NSUInteger index = originalString.length; index > 0; index--) {
char *character = [originalString characterAtIndex:index];
reverseString = [reverseString stringByAppendingString:[NSString stringWithFormat:@"%s", character]];
}
答案 12 :(得分：0)
-(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;
}
答案 13 :(得分：0)
夫特：
let string = "reverse"
let reversedStringCollection = string.characters.reversed()
for character in reversedStringCollection {
reversedString.append(character)
print(reversedString)
}
答案 14 :(得分：0)
以下是Objective-C中的类别集合，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'
答案 15 :(得分：-1)
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]];
}
答案 16 :(得分：-1)
为NSString添加一个类别，以便将来可以在任何NSString上调用reverse，如下所示：
#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
答案 17 :(得分：-2)
为此目的，我有两个简单的解决方案：
+(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，让我们测试吧！
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
更多的结果是：
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
与上述功能相同的文字：
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，选择表现！
答案 18 :(得分：-2)
我写了一个类别：D
//的NSString + Reversed.h #import
//
// NSString+Reversed.h
// HTMLPageFormatter
// Created by beit46 on 21.06.13.
//
@interface NSString (Reversed)
- (NSString *)reversedString;
@end
//的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