我说常说v这个变量时，表示它是在栈里。
我们说v这个对象，表示是v这个变量指向的对象，但凡是指向的某个对象，都是在堆里。

字符串的一些常用方法

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {

    [super viewDidLoad];

#if 0

    NSString *str = @"hello world";

    

    NSString *str2 = @"hello world_";

//    str2 = str;

    

    NSLog(@"str = %p",str);

    NSLog(@"str2 = %p",str2);

    

    NSString *s1 = @"hello world";

    s1 = @"hello welcome";

#endif

    

    NSString *str = @"hello world welcome to here";

    //从下标0位打印到10止

    NSString *subString = [str substringWithRange:NSMakeRange(0, 10)];

    NSLog(@"subString = %@",subString);

    //从下标第6位打印到结束

    subString = [str substringFromIndex:6];

    NSLog(@"subString = %@",subString);

    //打印到第6位结束

    subString = [str substringToIndex:6];

    NSLog(@"subString = %@",subString);

   

#if 0

    NSString *str1 = @"hello world";

    NSString *str2 = @"hello world_";

    

    if(str1 == str2){

    

        NSLog(@"==");

    }

#endif

   

#if 0

    NSString *url = @"http://xxx.xxx.com";

    

    //打印conrains包含的

    if([url containsString:@"xxx"]){

    

        NSLog(@"xxx");

    }

    //打印以这个结尾的

    if([url hasSuffix:@"com"]){

    

        NSLog(@"com");

    }

    //打印以这个开头的

    if([url hasPrefix:@"http"]){

    

        NSLog(@"http");

    }

    

#endif

    

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

    NSLog(@"%ld",range.location);

    if(range.location == NSNotFound){

    

    }

   

    //拼接地址

    NSString *basePath = @"base";

    //不会自动生成 / 符号

    NSString *finalPath = [basePath stringByAppendingString:@"/Documents"];

    //自动生成 / 符号

    [basePath stringByAppendingPathComponent:@"Documents"];

    

    //整数转化为字符串

    NSString *numStr = @"55";

    numStr.integerValue;

    NSInteger a = 55;

    [NSString stringWithFormat:@"%ld",a];

    

    //全部都转换为小写

    NSString *name = @"ZhangSAN";

    NSLog(@"name = %@",[name lowercaseString]);

    

    //把数据转换成UTF-8

    NSData *data = [@"hello world" dataUsingEncoding:NSUTF8StringEncoding];

    

    //将字符串转化为数组

    NSArray *arr = [str componentsSeparatedByString:@"world"];

    NSLog(@"arr = %@",arr);

    

    //打印的zhangsan这个名字前面有很多的空格，空格是占用空间的。

    NSString *userName = @"       zhangsan";

    NSLog(@"userName = %@",userName);

    //这个方法是把多余的空格都去掉。

    NSString *finalUserName = [userName stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];

    NSLog(@"finalUserName = %@",finalUserName);

    

    //把特定的字符都改写成我们需要的字符，让某些内容不显示出来。比如说把world，改写成*号

    NSString *secrStr = [str stringByReplacingOccurrencesOfString:@"world" withString:@"*"];

    

    //把某个地址或者网址的文章，读取到文件里。

    NSString *contents = [NSString stringWithContentsOfFile:@"--filePath--" encoding:NSUTF8StringEncoding error:nil];

    //把某个地址或者网站的文章，写入到文件里。

    [@"contetns" writeToFile:@"--target path" atomically:YES encoding:NSUTF8StringEncoding error:nil];
   

}

@end