Objective-C:NSString类的常见用法

几种常见的用法为：字符串的创建、字符串的搜索、字符串的比较、字符串的转换

用途一：字符串的创建

 void ex1()
 {
     //1.常量字符串的对象
     NSString *str1 = @"hello world";
     NSLog(@"str1 = %@",str1);
     //2.通过类方法创建字符串
     NSString *str2 = [NSString stringWithString:str1];
     NSLog(@"str2 = %@",str2);
     //3.通过实例方法创建
     NSString *str3 = [[NSString alloc]initWithString:str1];
     NSLog(@"str3 = %@",str3);
     //4.格式化字符串方式创建
     NSString *str4 = [NSString stringWithFormat:@"name=%@,password=%@",@"admin",@""];
     NSLog(@"str4 = %@",str4);
     //5.通过C语言字符串的创建
     char *pstr = "how are you?";
     NSString *str5 = [NSString stringWithUTF8String:pstr];
     NSLog(@"str5 = %@",str5);
     //6.通过文件的方式创建字符串
     NSError *error = nil;
     NSUInteger enc;
     NSString *str6 = [[NSString alloc]initWithContentsOfFile:@"/Users/mac/Java/IO/2.txt" usedEncoding:&enc error: &error];
     if(!error)
     {
         NSLog(@"str6 = %@",str6);
     }
     else
     {
         NSLog(@"读取文件失败:%@",error);
     }
     //7.通过网络数据创建字符串
     NSURL *url = [NSURL URLWithString:@"http://www.baidu.com"];
     NSString *str7 = [NSString stringWithContentsOfURL:url encoding:NSUTF8StringEncoding error:&error];
     if(!error)
     {
         NSLog(@"str7 = %@",str7);
     }
     else
     {
         NSLog(@"读取网络失败:%@",error);
     }
 }

用途二：字符串的搜索

 void ex2()
 {
     //1.搜索字符串
     NSString *str = @"this is a test";
     NSRange nsr = [str rangeOfString:@"test"];//返回一个结构体
     if(nsr.length != )//找到字符串
     {
       NSLog(@"location=%lu,length=%lu",nsr.location,nsr.length);
     }
     //2.查找字符串是不是以什么前缀开始
     NSString *str2 = @"http://www.sina.com.cn";
     if([str2 hasPrefix:@"http"])
     {
         NSLog(@"http协议");
     }
     //3.查找字符串是不是以什么后缀开始
     NSString *str3 = @"1.txt";
     if([str3 hasSuffix:@"txt"])
     {
         NSLog(@"文本文件");
     }
     //4.在字符串中截取字串
     NSString *str4 = @"http://www.sxt.cn?user=admin&password=1233456";
     NSRange range1 = [str4 rangeOfString:@"user="];
     NSRange range2 = [str4 rangeOfString:@"&password="];

     //求出user的字符串区间并输出字符串
       //用户名起始位置
     NSUInteger location = range1.location + range1.length;
       //用户名的有效长度
     NSUInteger length = range2.location - location;

     NSRange range3 = NSMakeRange(location,length);
     NSString *user = [str4 substringWithRange:range3];

     //求出password的字符串
     NSString *password = [str4 substringFromIndex:range2.location+range2.length];

     NSLog(@"user=%@,password=%@",user,password);
 }

用途三：字符串的比较

 void ex3()
 {
     //对象比较
     //1.判断两个对象是不是同一个对象
     NSString *str1 = @"hello world";
     NSString *str2 = @"how are you";
     NSString *str3 = str1;
     if(str1 == str3)
     {
         NSLog(@"str1和str3是同一个对象");
     }
     //或者
     if([str1 isEqual:str3])
     {
         NSLog(@"str1和str3是同一个对象");
     }
     //或者
     if([str1 isEqualTo:str3])
     {
         NSLog(@"str1和str3是同一个对象");
     }

     //2.判断字符串是否相等
     if([str1 isEqualToString:@"hello world"])
     {
         NSLog(@"字符串相等");
     }

     //3.字符串的比较
     NSComparisonResult result = [str1 compare:str2];
     if(result== NSOrderedSame)
     {
         NSLog(@"两个字符串相等");
     }
     else if(result == NSOrderedAscending)
     {
         NSLog(@"第一个小于第二个字符串");
     }
     else
     {
         NSLog(@"第一个大于第二个字符串");
     }
 }

用途四：字符串的转换

 void ex4()
 {
     //1.其它类型转换成字符串
     NSString *str1 = [NSString stringWithFormat:@"%D,%.2f,%c,%s",,12.34,'A',"hello world"];
     NSLog(@"str1 = %@",str1);

     //2.字符串转换为整型
     NSString *str2 = @"";
     NSInteger  i = [str2 integerValue];
     NSLog(@"i = %ld",i);

     //3.字符串转换为实型
     NSString *str3 = @"12.34";
     CGFloat f = [str3 doubleValue];
     NSLog(@"f = %.2f",f);

     //4.字符串转换为C语言的字符串
     NSString *str4 = @"how are you";
     const char *pstr = [str4 UTF8String];
     NSLog(@"pstr = %s",pstr);

 }