OC - NSString

//定义不可变字符串.
NSString *s1 = @"abc";
//初始化
NSString *s2 = [[NSString alloc]init];
//便利构造器
NSString *s3 = [NSString string];
//以上两个初始化方法都不常用.

   
//格式化初始化字符串
    NSString *s4 = [[NSString alloc]initWithFormat:@"abc"];
    NSLog(@"%@",s4);

    NSString *s5 = [NSString stringWithFormat:@"def"];

    NSLog(@"%@",s5);
    NSString *s6 = [NSString stringWithFormat:@"%d123",456];

    NSLog(@"%@",s6);

   

//通过文件路径获取文件里的内容.

    NSString *s7 = [NSString stringWithContentsOfFile:@"/Users/root/Desk/123.txt" encoding:NSUTF8StringEncoding error:nil];

   

    NSLog(@"%@",s7);

   

//表示求s6字符串长度.

    NSLog(@"%lu",[s6 length]);

   

//判断是否有前后缀

    NSString *s8 = @"abc123";

    BOOL b1 = [s8 hasPrefix:@"abc"];

    NSLog(@"%d",b1);

    BOOL b2 = [s8 hasSuffix:@"123"];

    NSLog(@"%d",b2);
   
//大小写转换  
注意!!!一定要有返回值接收!!!   
NSString *s9 = [s8 uppercaseString];
    NSLog(@"%@",s9);

    NSString *s10 =[s9 lowercaseString];
    NSLog(@"%@",s10);

//将某个字符串里所有的单词都变成首字母大写;
    NSMutableString

*d1 = [NSMutableStringstringWithFormat:@"i
love you somuch."];

   
NSLog(@"%@",d1);

   
NSString
*d2 = [d1
capitalizedString];
   NSLog(@"%@",d
2);
//比较字符串

    NSComparisonResult r1 = [s8 compare:s9];

    NSLog(@"%ld",r1);

   

//比较字符串是否相等,也可以用第一个.

    BOOL b3 = [s8 isEqualToString:s9];

    NSLog(@"%d",b3);

   

//选取某位字符,(字符串计算从0位开始)

    NSLog(@"%c",[s8 characterAtIndex:1]);

   

//从第x为开始截取字符串一直到最后,包括第x位.

    NSString *s11 = [s8 substringFromIndex:1];

    NSLog(@"%@",s11);
   
//从x位开始,包括第x位,以后的字符串全部截掉,只保留前x位.
    NSString *s12 = [s8 substringToIndex:1];

    NSLog(@"%@",s12);
  
//以字符串中的某个字符为界限,讲字符串分成两部分.
   NSMutableString*f1
= [NSMutableStringstringWithFormat:@"20|http://www.baidu.com"];

     NSArray*arr1 = [f1

componentsSeparatedByString:@"|"];
   NSLog(@"%@",arr1);
    打印结果(必须用数组接收):
                    20,                         
                   "http://www.baidu.com"

    //从x位开始,截取长度为y的字符串.包括第x位.

    NSString *s13 = [s8 substringWithRange:NSMakeRange(1, 3)];

    NSLog(@"%@",s13);