Object-C-NSString

NSString *info=@"Hello world";

NSString *info=[[NSString alloc]initWithFormat:@"my name is %@",name];

将char 类型的字符串和 NSString 进行转换

char *cStr = "i am  c string";

NSString *str=[[NSString alloc] initWithCString: cStr encoding: (编码方法通常是utf8)];

NSString *str2=@"hello";

char *cstr2 = [str2 UTF8String];

使用快捷方法进行字符串创建和初始化，stringWith开头方法

此种方法创建的字符串对象在非ARC环境下不需要释放

　　 NSString *name =@"tom";

　　 NSString *info=[NSString stringWithFormat:@"my name is %@",name];字符串的大小比较 compare方法

　　 NSString *str1 =@"tom";

　　 NSString *str2 = @"jack";

　　 [str1 compare:str2];

NString *str1 = @"tom";

NString *str2 = @"jack";

NSComparisonResult result = [str1 compare:str2];

if(result==NSOrderedAscending)

{

NSLog(@"str1<str2");

}else if(result==NSOrdereDescending)

{

NSLog(@"str1>str2");

}else       NSLog(@"str1==str2");

字符串是否相等[username isEqualToString:@"admin"]

字符串长度

[username length];

寻找子串rangeOfString返回类型NSRange 不存在时location 为NSNotFound

NSString *str = @"hello world";

NSRange range=[str rangeOfString:@"lloc"];可以查看NSRange的类型

子串的截取

字符串和文件以及文件路径,writeToFile,initWithContentsOfFele

NSString *str =@"i am a string";

BOOL result=[str writeToFile:@"/Users/administator/Desktop/1.txt" atomically:YES encoding:NSUTF8StringEncoding error:nil];

NSString *content=[[NSString alloc]initWithContentsOfFile:@"/Users/administator/Desktop/1.txt",encoding:NSUTF8StringEncoding error:nil];

NSMutableString 是 NSString 的子类

NSMUtableString *str=[NSMutableString stringWithCapacity:20];

[str appendString:@"123"]; str后面加上123字符串

[str insertString:@"age is " atIndex:0];插入

[str deleteCharactersInRange:NSMakeRange(4,2)];删除

[str replaceCharactersInRange:NSMakeRange(5,2) withString:@"22"];替换

[str setString:;@"22"]; 重置

//一.不变字符串

        //1.常量字符串，比较字符串
//        NSString *str1 = @"hello world";
//        NSString *str2 = @"hello world";
//        if (str1==str2) {
//            NSLog(@"equal");
//        }
//        else
//        {
//            NSLog(@"unequal");
//        }
//        NSLog(@"str1 address  is %p",str1);
//        NSLog(@"str2 address  is %p",str2);
        //使用init方法进行创建
//        NSString *name = @"tom";
//        NSString *info = [[NSString alloc] initWithFormat:@"my name is %@",name];
//        NSLog(@"%@",info);
        //2.使用快捷方法进行字符串的创建和初始化
//        NSString *name = @"tom";
//        NSString *info = [NSString stringWithFormat:@"my name is %@",name];
//        NSLog(@"%@",info);
       //3.大小写转换及前后缀
//        NSLog(@"\"Hello world!\" to upper is %@",[@"Hello world!" uppercaseString]);
//        NSLog(@"\"Hello world!\" to lowwer is %@",[@"Hello world!" lowercaseString]);
          //前缀
         // NSLog(@"has prefix ab? %i",[@"abcdef" hasPrefix:@"abd"]);
//          //后缀
         // NSLog(@"has suffix ab? %i",[@"abcdef" hasSuffix:@"ef"]);
        //4.字符串的比较
       // NSString *str1 = @"tom";
//        NSString *str2 = @"eric";
//        NSComparisonResult result= [str1 compare:str2];
//        if (result==NSOrderedAscending) {
//            NSLog(@"str1<str2");
//        }
//        else if (result ==NSOrderedDescending)
//        {
//            NSLog(@"str1>str2");
//        }
//        else
//        {
//            NSLog(@"str1==str2");
//        }

        //5.char类型和NSString类型转换
//        char *str= "test case";
//        NSString *str3= [[NSString alloc] initWithCString:str encoding:NSUTF8StringEncoding];
//        char *str4 = (char *)[str3 UTF8String];
//        NSLog(@"%s",str4);
        //6.字符串值的比较
//        NSString *username = @"admin";
//        NSString *password = @"123456";
//        if ([username isEqualToString:@"admin"] && [password isEqualToString:@"123456"]) {
//            NSLog(@"值相等");
//        }
//        else
//        {
//            NSLog(@"值不相等");
//        }
        // 7.字符串的长度
//        NSString *str =@"alfred";
//        if ([str length]>=6) {
//            NSLog(@"the length is %lu",[str length]);
//        }
//        else
//        {
//            NSLog(@"ok");
//        }
        //8.字符串截取
//        NSLog(@"%@",[@"abcdef" substringFromIndex:3]);//从第三个索引开始（包括第三个索引对应的字符）截取到最后一位
//        //结果：def
       // NSLog(@"%@",[@"abcdef" substringToIndex:3]);////从0开始截取到第三个索引（不包括第三个索引对应的字符）
//        //结果：abc
       // NSLog(@"%@",[@"abcdef" substringWithRange:NSMakeRange(2, 3)]);

        //9.数值转换
//        NSString *value1 = @"10";
//        NSString *value2 = @"3.6";
//        float sum = [value1 intValue] +[value2 floatValue];
//        NSLog(@"%0.2f",sum);
        //10.文件相关
//        NSString *str =@"i am a string abc";
//        [str writeToFile:@"/Users/admin/Desktop/test2.txt" atomically:YES encoding:NSUTF8StringEncoding error:nil];
//        NSString * str2 = [[NSString alloc] initWithContentsOfFile:@"/Users/admin/Desktop/test2.txt" encoding:NSUTF8StringEncoding error:nil];
//        NSLog(@"%@",str2);
        //NSString *str3 = [NSString alloc]
//        

        //二.可变字符串

      //NSMutableString *str = [NSMutableString stringWithCapacity:20];
        NSMutableString *str2 = [[NSMutableString alloc]init];
        [str2 setString:@"test case"];
     //   [str appendString:@"12"];
//        NSString *name = @"tom";
//        [str appendFormat:@",name is %@",name];
       // [str replaceCharactersInRange:NSMakeRange(4, 2) withString:@"22"];
       // [str insertString:@"it is" atIndex:3];
        [str2 deleteCharactersInRange:NSMakeRange(, )];
         NSLog(@"str = %@",str2);

ie

  NSMutableArray *array = [[NSMutableArray alloc] init];
         [array addObject:@"tom"];
         NSNumber *num = [NSNumber numberWithInt:]; //装箱
         [array addObject:num];
         [array addObject:[NSNumber numberWithFloat:3.5]];
         NSNumber *numobj=[array objectAtIndex:];
         NSLog(@"%d",[numobj intValue]); //拆箱

         //NSValue
         NSRange range;
         range.location =;
         range.length =;
         NSValue *value=[NSValue valueWithRange:range];
         NSLog(@"%@",value);
         //NSNull
         NSArray *arr = [NSArray arrayWithObjects:@"tom" ,[NSNull null],nil];
         for (int i =; i<[arr count]; i++) {
             if ([arr objectAtIndex:i]!=[NSNull null]) {
                 NSLog(@"%@",[arr objectAtIndex:i]);
             }
             else
             {
                 NSLog(@"第%d个元素是空值",i);
             }
         }
         //测试NSNull单例
         NSNull *nl=[NSNull null];
         NSNull *nl2=[NSNull null];
         NSLog(@"%i",nl==nl2);//由于是单例所以地址相等,结果：1
         NSArray *array1=[NSArray arrayWithObjects:@"abc",nl,@, nil];
         NSLog(@"%@",array1);