OC字符串的一些常用的函数。

1）//获取字符串长度
NSUInteger len= str.length;
（2） //通过指定索引返回对应的字符
unichar ch =[str characterAtIndex:5];
（3）//通过指定格式对字符串进行初始化
NSString *str1=[NSStringstring];
        NSLog(@"%@",str1);
        NSString *str2=[[NSString alloc] initWithFormat:@"this is a %@",@"cat" ];
        NSLog(@"%@",str2);
        NSString *str3=[NSString stringWithFormat:@"this is a %@",@"cat"];
        NSLog(@"%@",str3);
（4）//将c语言字符数组转换成oc语言字符串；
        char *chs="guiyang";
        //printf("%s",chs);
        NSString *str5=[[NSString alloc]initWithCString:chs encoding:NSUTF8StringEncoding];
        NSLog(@"%@",str5);
        NSString *str6=[[NSString alloc]initWithUTF8String:chs];
        NSLog(@"%@",str6);
        NSString *str7=[NSString stringWithUTF8String:chs];
        NSLog(@"%@",str7);
        NSString *str8=[NSString stringWithCString:chs encoding:NSJapaneseEUCStringEncoding];
        NSLog(@"%@",str8);
int c=a-b;
        NSString *str1=[NSString stringWithFormat:@"%d",c];
        NSLog(@"%@",str1);
（5） //将oc语言变成C语言
        NSString *ch1=@"student";
        char *ch2=(char *)[ch1 UTF8String];
        NSLog(@"%s",ch2);
（6）//从字符串第7个数开始，往后输出
        NSString *str10=@"guiyangxueyuan";
        NSString *ch3=[str10 substringFromIndex:7];
        NSLog(@"%@",ch3);
（7） //从字符串一直输出到第7个，
        NSString *str10=@"guiyangxueyuan";
        NSString *ch4=[str10 substringToIndex:7];
        NSLog(@"%@",ch4);
（8） //范围结构体 两个参数，第一个 位置，第二个 个数
        NSString *str10=@"guiyangxueyuan";
        NSRange range;
        range.location=7;
        range.length=3;
        NSString *ch5=[str10 substringWithRange:range];
        NSLog(@"%@",ch5);
（9） //输出@前面的字符串
        NSString *str11=@"张云江@qq.com";
        NSRange  range1=[str11 rangeOfString:@"@"];
        if (range1.location==NSNotFound) {
            NSLog(@"sorry");
        }
        else{
        NSString *ch6=[str11 substringToIndex:range1.location];
            NSLog(@"hello,%@",ch6);
        }
    }
(10)//判断两个字符串是否相等
        NSString *ch=[NSString stringWithFormat:@"ABC"];
        NSString *ch1=[NSString stringWithFormat:@"abc"];
        BOOL result=[ch1 isEqualToString:ch];
        （a）查看地址
        NSLog(@"%p",[str2 description]);
        NSLog(@"%p",[str3 description]);]);
(11) //比较字符串大小，-1 0 1；
        NSString *str1=@"guiyang";
        NSString *str2=@"GuiYang";
        NSLog(@"%ld",[str1 caseInsensitiveCompare:str2]);
        NSLog(@"%ld",[str1 compare:str2 options:NSCaseInsensitiveSearch]);
        NSComparisonResult result =  [str1 compare:str2];

        NSLog(@"result=%ld",result);
        if ([str1 compare:str2]==NSOrderedAscending) {
            NSLog(@"小于");
        }
        else if ([str1 compare:str2]==NSOrderedDescending)
        {
            NSLog(@"大于");
        }
        else {
            NSLog(@"相等");/        }
    //方法1忽略大小写
        NSComparisonResult result1=[ch compare:ch1 options:NSCaseInsensitiveSearch];
        NSLog(@"%ld",result1);
    //方法2忽略大小写
        NSLog(@"%ld",[ch caseInsensitiveCompare:ch1]);

(12)//判断开头和结尾
NSString *ch2=[NSString stringWithFormat:@"https//baidu.com"];
        bool bol=[ch2 hasSuffix:@".com"];
        NSLog(@"%d",bol);
        bool bol1=[ch2 hasPrefix:@"https"];
        NSLog(@"%d",bol1);

(13)//字符串转换为整型
        NSString *sh=@"1200";
        NSLog(@"%d",[sh intValue]+3000)；

(14)//将字母大写
        NSString *sh1=@"name is xxx";
        NSLog(@"%@",[sh1 uppercaseString]);
        //将首字母大写
        NSLog(@"%@",[sh1 capitalizedString]);

(15)//改变
        NSString *ch=@"guiyangxueyuan";
        NSString *ch1=[ch stringByReplacingOccurrencesOfString:@"yuan" withString:@"YUAN"];
        NSLog(@"%@",ch1);
(16)//分段
        NSString *ch=@"136-2561-2365";
        NSArray *rr=[ch componentsSeparatedByString:@"-"];
        NSLog(@"%@",rr);
(17)//连接字符串
        NSMutableString *sh=[NSMutableString stringWithCapacity:100];
        [sh appendFormat:@"我的名字叫李斯 "];
        [sh appendFormat:@"今年22岁"];
        NSLog(@"%ld",[sh length]);
        NSLog(@"%@",sh);
(18)//中间插入字符串
        [sh insertString:@"我的自我介绍：" atIndex:0];
        NSLog(@"%@",sh);
(19)//修改
        NSRange range=[sh rangeOfString:@"我的自"];
        [sh replaceCharactersInRange:range withString:@"这是"];
        NSLog(@"%@",sh);
(20)//字符串 替换函数
        NSString *str12=@"集训ios开班典礼";

        NSString *str13 =[str12 stringByReplacingOccurrencesOfString:@"开班" withString:@"结业"];

        NSLog(@"%@",str13);
(21)//删除
      NSRange range1=[sh rangeOfString:@"叫李"];
        [sh deleteCharactersInRange:range1];
        NSLog(@"%@",sh);
(22)//给可变字符串分配空间（初始化）
       NSMutableString *str1 =[NSMutableString stringWithCapacity:10];
(23)//可变字符串追加方法
        [str1 appendFormat:@"name is %@",@"lisi,"];
        [str1 appendString:@"age is 22,"];
        [str1 appendString:@"addr is guiyang"];