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",@"123456"];
    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 != 0)//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",10,12.34,'A',"hello world"];
    NSLog(@"str1 = %@",str1);
    
    //2.字符串转换为整型
    NSString *str2 = @"20";
    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);
    
}