NSString其實是一個物件型別。NSString是NSObject（Cocoa Foundation的基礎物件）的子類

一、NSString的建立

1、建立常量字串。
NSString *astring = @"This is a String!";

2、建立空字串，給予賦值。
NSString *astring = [[NSString alloc] init];
astring = @"This is a String!";
[astring release];
NSLog(@"astring:%@",astring);

NSString *astring = [[NSString alloc] init];
NSLog(@"0x%.8x", astring);

[email protected]"This is a String!";
NSLog(@"0x%.8x", astring);
[astring release];
NSLog(@"astring:%@",astring);

3、在以上方法中，提升速度:initWithString方法
NSString *astring = [[NSString alloc] initWithString:@"This is a String!"];
NSLog(@"astring:%@",astring);
[astring release];

4、用標準c建立字串:initWithCString方法

char *Cstring = "This is a String!";
NSString *astring = [[NSString alloc] initWithCString:Cstring];
NSLog(@"astring:%@",astring);
[astring release];

5、建立格式化字串:佔位符（由一個%加一個字元組成）
int i = 1;
int j = 2;
NSString *astring = [[NSString alloc] initWithString:[NSString stringWithFormat:@"%d.This is %i string!",i,j]];
NSLog(@"astring:%@",astring);
[astring release];

6、建立臨時字串
NSString *astring;
astring = [NSString stringWithCString:"This is a temporary string"];
NSLog(@"astring:%@",astring);

7、寫字串到檔案:writeToFile方法    
NSString *astring = [[NSString alloc] initWithString:@"This is a String!"];
NSLog(@"astring:%@",astring);
NSString *path = @"astring.text";    
[astring writeToFile: path atomically: YES];
[astring release];  

8、從檔案讀取字串:initWithContentsOfFile方法 
NSString *path = @"astring.text";
NSString *astring = [[NSString alloc] initWithContentsOfFile:path];
NSLog(@"astring:%@",astring);
[astring release];

二、字串的比較

1、用C比較:strcmp函式
char string1[] = "string!";
char string2[] = "string!";
if(strcmp(string1, string2) = = 0)
{
NSLog(@"1");
}

2、isEqualToString方法    
NSString *astring01 = @"This is a String!";
NSString *astring02 = @"This is a String!";
BOOL result = [astring01 isEqualToString:astring02];
NSLog(@"result:%d",result);

3、compare方法(comparer返回的三種值)    
NSString *astring01 = @"This is a String!";
NSString *astring02 = @"This is a String!";    
BOOL result = [astring01 compare:astring02] = = NSOrderedSame;    
NSLog(@"result:%d",result);    
//NSOrderedSame判斷兩者內容是否相同

NSString *astring01 = @"This is a String!";
NSString *astring02 = @"this is a String!";
BOOL result = [astring01 compare:astring02] = = NSOrderedAscending;    
NSLog(@"result:%d",result);
//NSOrderedAscending判斷兩物件值的大小(按字母順序進行比較，astring02大於astring01為真)

不考慮大小寫比較字串
NSString *astring01 = @"this is a String!";
NSString *astring02 = @"This is a String!";
BOOL result = [astring01 caseInsensitiveCompare:astring02] = = NSOrderedSame;    
NSLog(@"result:%d",result);     
//NSOrderedDescending判斷兩物件值的大小(按字母順序進行比較，astring02小於astring01為真)

不考慮大小寫比較字串2
NSString *astring01 = @"this is a String!";
NSString *astring02 = @"This is a String!";
BOOL result = [astring01 compare:astring02
options:NSCaseInsensitiveSearch | NSNumericSearch] = = NSOrderedSame;    
NSLog(@"result:%d",result);     
P.S : NSCaseInsensitiveSearch:不區分大小寫比較 NSLiteralSearch:進行完全比較，區分大小寫 NSNumericSearch:比較字串的字元個數，而不是字元值。

三、改寫字串

NSString *string1 = @"A String"; 
NSString *string2 = @"String"; 
NSLog(@"string1:%@",[string1 uppercaseString]);//大寫
NSLog(@"string2:%@",[string2 lowercaseString]);//小寫
NSLog(@"string2:%@",[string2 capitalizedString]);//首字母大小

四、搜尋字串

NSString *string1 = @"This is a string";
NSString *string2 = @"string";
NSRange range = [string1 rangeOfString:string2];
int location = range.location;
int leight = range.length;
NSString *astring = [[NSString alloc] initWithString:[NSString stringWithFormat:@"Location:%i,Leight:%i",location,leight]];
NSLog(@"astring:%@",astring);
[astring release];

五、字串的擷取

1.-substringToIndex: 從字串的開頭一直擷取到指定的位置，但不包括該位置的字元
NSString *string1 = @"This is a string";
NSString *string2 = [string1 substringToIndex:3];
NSLog(@"string2:%@",string2);

2.-substringFromIndex: 以指定位置開始（包括指定位置的字元），幷包括之後的全部字元
NSString *string1 = @"This is a string";
NSString *string2 = [string1 substringFromIndex:3];
NSLog(@"string2:%@",string2);

3.-substringWithRange: //按照所給出的位置，長度，任意地從字串中擷取子串
NSString *string1 = @"This is a string";
NSString *string2 = [string1 substringWithRange:NSMakeRange(0, 4)];
NSLog(@"string2:%@",string2);

4.擷取NSString最後一位符號後的東西

方法1.

NSString *str = @"/Users/yangiori/Library/Application Support/iPhone Simulator/5.1/Applicati*****/8724956B-407E-4ACD-BBA6-95C7D033C33D/Documents/content/chapters/8";
NSString *temp1 = [[str componentsSeparatedByString:@"/"] lastObject];
NSLog(@"%@",temp1);

結果：8

方法2.

NSString *str = @"/Users/yangiori/Library/Application Support/iPhone Simulator/5.1/Applicati*****/8724956B-407E-4ACD-BBA6-95C7D033C33D/Documents/content/chapters/8";

NSString *temp2 = [str substringFromIndex:[str length]-1];

NSLog(@"%@",temp2);

結果：8

5.從指定位置擷取字串

NSString * str =[NSString stringWithFormat:@"********************Documents/image%i.jpg",2];

NSRange range = [str rangeOfString:@"Documents"]; 

NSString * result = [str substringFromIndex:range.location]; 

NSLog(@"%@",result);

六、其他操作

1.擴充套件路徑
NSString *Path = @"~/NSData.txt";
NSString *absolutePath = [Path stringByExpandingTildeInPath];
NSLog(@"absolutePath:%@",absolutePath);
NSLog(@"Path:%@",[absolutePath stringByAbbreviatingWithTildeInPath]);

2.副檔名
NSString *Path = @"~/NSData.txt";
NSLog(@"Extension:%@",[Path pathExtension]);

NSMutableString

基本用法

1.給字串分配容量

stringWithCapacity:
NSMutableString *String;
String = [NSMutableString stringWithCapacity:40];

2.在已有字串後面新增字元

appendString: and appendFormat:
NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is a NSMutableString"];
[String1 appendString:@", I will be adding some character"];
[String1 appendFormat:[NSString stringWithFormat:@", I will be adding some character"]];
NSLog(@"String1:%@",String1);

3.在已有字串中按照所給出範圍和長度刪除字元

deleteCharactersInRange:
NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is a NSMutableString"];
[String1 deleteCharactersInRange:NSMakeRange(0, 5)];
NSLog(@"String1:%@",String1);

4.在已有字串後面在所指定的位置中插入給出的字串

-insertString: atIndex:
NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is a NSMutableString"];
[String1 insertString:@"Hi! " atIndex:0];
NSLog(@"String1:%@",String1);

5.將已有的空符串換成其它的字串

-setString:
NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is a NSMutableString"];
[String1 setString:@"Hello Word!"];
NSLog(@"String1:%@",String1);

6.按照所給出的範圍，和字串替換的原有的字元

-setString:
NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is a NSMutableString"];
[String1 replaceCharactersInRange:NSMakeRange(0, 4) withString:@"That"];
NSLog(@"String1:%@",String1);

7.判斷字串內是否還包含別的字串(字首，字尾)

01：檢查字串是否以另一個字串開頭- (BOOL) hasPrefix: (NSString *) aString;
NSString *String1 = @"NSStringInformation.txt";
[String1 hasPrefix:@"NSString"] = = 1 ?  NSLog(@"YES") : NSLog(@"NO");
[String1 hasSuffix:@".txt"] = = 1 ?  NSLog(@"YES") : NSLog(@"NO");

02：查詢字串某處是否包含其它字串 - (NSRange) rangeOfString: (NSString *) aString，這一點前面在串中搜索子串用到過;