OC字符串

//1. 通过简单的字符串创建
       NSString *str =@"hello";
       
       //2.使用NSString实例方法
       //NSString *str1 = [[NSString alloc]initWithString:str];
       NSString  *str1 = [NSStringstringWithString:str];
       //3.使用格式化的方法
       //NSString *str2 = [[NSString alloc]initWithFormat:@"str%i",4];
       NSString  *str2 = [NSStringstringWithFormat:@"str%i",4];
       //4.通过一个C语言的字符串
       NSString*str3 = [NSStringstringWithUTF8String:"hello"];
       //5.通过读文件的方式创建字符串
       NSString  *error =nil;
       NSString  *path =@"/Users/Chris/Desktop/first/OC/2.txt";
       NSString  *str4 = [NSStringstringWithContentsOfFile:pathencoding:NSUTF8StringEncodingerror:&error];
       
       if(error) {
           NSLog(@"%@",error);
        }
       
       //6.通过网页的内容创建字符串
       error =nil;
       NSURL*url = [NSURLURLWithString:@"http://www.baidu.com"];
       NSString*str5 = [NSStringstringWithContentsOfURL:urlencoding:NSUTF8StringEncodingerror:&error];
       if(error) {
           NSLog(@"%@",error);
        }