OC中Foundation框架之NSString

 1 1)直接赋值
 2     NSString *str =@"abc";
 3 2）创建对象
 4     NSString *str2 = [[NSString alloc]init];
 5                     str2 =@"abc"
 6 3）格式化创建
 7      NSString *str3=[NSString stringWithFromat :@"@",@"abc"];
 8                      
 9 4)从文件中获取
10     NSString strand =[NSString stringWithContentsOfFile:@"/Users/apple/Desktop/test.txt" usedEncoding:NSUTF8StringEncoding error:&err];
11 
12 
13 5)把字符串写入到文件
14     NSString *str7 = @"abc";
15                                             //路径                            //原子性
16                     str7 writeToFile :(NNString *) atomically :(BOOL)
17               //编码格式                         //错误信息
18  encoding:(NSStringEncoding) error:(NSError **);
19 
20 
21     NSERROR *err=nil;
22     BOOL flag=str7 writeToFile:@"/Users/apple/Desktop/test.txt" atomically:NO encoding : NSUTF8StringEncoding error:(&err];
23     if(flag){
24         NSLog(@"写入成功");
25     }
26 
27     if(err != nil){
28         NSLog(@"写入失败");
29     }else{
30         NSLog(@"写入成功");
31     }

 1 //1)使用NSURL 写入字符串数据到文件中
 2 
 3 NSURL *writeUrl = [NSURL URLWithString:@"file:///Users/apple/Desktop/1.txt"];
 4 
 5 NSString *str =@"itcast";
 6 
 7 BOOL isSucess = str writeToURL :writeUrl atomically:NO encoding:NSUTF8StringEncoding error:nil];
 8 
 9 if(isSucess){
10     NSLog(@"写入成功");
11 }
12 
13 
14 
15 //2)使用NSURL读取字符串到文件
16 
17 NSURL *readUrl =[NSURL URLWithString:@"file:////Users/apple/Desktop/1.txt"]
18 NSString *straighten = [NSString stringWithContentsOfURL:readUrl encoding :NSUTF8StringEncoding error:nil];
19 NSLog(@"%@",str2);