Objective-C字符串初识（上）

1.创建字符串

 1         // 1 直接创建字符串
 2         NSString * str = @"abc";
 3
 4 //       NSString * stra = [[NSString alloc] initWithString:@"def"];
 5         // 2 用C语言字符串创建OC字符串
 6　　　　　 char * p = "你好";

 7         NSString * strc = [[NSString alloc] initWithCString:p encoding:NSUTF8StringEncoding];

 8         NSLog(@"cstr %@",strc);
 9         // 3 格式化的方式创建字符串
10         // format
11         int age = 19;
12
13         NSString * strf = [[NSString alloc] initWithFormat:@"%d岁上的%@",age,@"大二"];
14         NSLog(@"%@",strf);

2. 字符串的拼接

 1     /*
 2      //1.已知有两个字符串NSString * str1 = @“hello” NSString * str2 =  @“world”，将两个字符串拼接到一起，生成新字符串str，中间用空格分开。
 3
 4      @"hello world"
 5      */
 6
 9         // 用printf函数打印 "hello world"
10         printf("%s %s",a,b);
11         NSString * str1 = @"hello";
12         NSString * str2 = @"world";
13
14         NSLog(@"%@ %@",str1,str2);
15
16         NSString * str3 = [[NSString alloc] initWithFormat:@"%@ %@",str1,str2];
17
18         NSLog(@"format: %@",str3);
19         

3.获取长度以及单个字符

 1         // 1 获取字符串的长度
 2         NSString * str = @"qianfeng";
 3         // 获取长度
 4         NSUInteger length = [str length];
 5         NSLog(@"%lu",length);
 6
 7         // 2 获取单个字符
 8         unichar c = [str characterAtIndex:7];
 9         // %c
10         NSLog(@"%C",c);

4.获取子串

　　4.1 index截取前/后 子串

1         // 截取从index开始到结尾的字符串(包括index)
2         NSString * subString1 = [str substringFromIndex:2];
3         NSLog(@"%@",subString1);
4         // 截取从开始到index的字符串(不包括index)
5         NSString * subString2 = [str substringToIndex:3];
6         NSLog(@"%@",subString2);

　　4.2 从X开始截取Y长度的子串

1         // www.baidu.com
2         // 截取 baidu
3         NSString * strB = @"www.baidu.com";
4         NSRange rangeB = NSMakeRange(4, 5);
5         NSString * subB = [strB substringWithRange:rangeB];
6         NSLog(@"%@",subB);

　　4.2 获取子串范围

 1             //3.已知字符串NSString * str2 = @“I love Beijing!”;
 2             //找出love的范围
 3
 4             NSString * str = @"I love Beijing!";
 5             NSRange range = [str rangeOfString:@"love"];
 6             if (range.location != NSNotFound) {
 7                 NSLog(@"%@",NSStringFromRange(range));
 8             } else {
 9                 NSLog(@"不存在");
10             }

1           //5.将字符串@"When I was young, I loved a girl in neighbor class."中，从young提取到girl。但是不许数。
2             NSString * str = @"When I was young, I loved a girl in neighbor class.";
3
4             NSRange rangeYoung = [str rangeOfString:@"young"];
5             NSRange rangeGirl = [str rangeOfString:@"girl"];
6             // 1234567 6-2
7             NSRange range = {rangeYoung.location,rangeGirl.location-rangeYoung.location+rangeGirl.length};
8             NSString * newStr = [str substringWithRange:range];
9             NSLog(@"%@",newStr);    

5.字符串的判断

　　5.1 空字符的判断

　　　　nil和@""都是空字符

1         NSString * str1 = @" ";
2         NSString * str = nil;
3         NSString * str2 = @"";
4         if (str1 == nil || [str1 length] == 0) {
5             NSLog(@"空字符串");
6         } else {
7             NSLog(@"非空");
8         }

　　5.2 判断是否以指定内容开头/结尾　　

 1         // 2 判断字符串是否以指定的内容开头
 2         NSString * str3 = @"www.qianfeng.com";
 3         BOOL hasPre = [str3 hasPrefix:@"www"];
 4         // YES NO
 5         NSLog(@"%d",hasPre);
 6         if (hasPre) {
 7             NSLog(@"是一个网址");
 8         } else {
 9             NSLog(@"不是一个网址");
10         }
11
12         // qianfeng.txt
13         NSString * str4 = @"qianfeng.txt";
14         BOOL hasSuf = [str4 hasSuffix:@"txt"];
15         if (hasSuf) {
16             NSLog(@"是txt");
17         } else {
18             NSLog(@"不是txt");
19         }

　　5.3判断字符串是否相等

 1         NSString * str5 = @"qianfeng";
 2         NSString * str6 = [[NSString alloc] initWithFormat:@"qianfeng"];
 3         NSString * str7 = @"qianfeng";
 4         NSString * str8 = [[NSString alloc] initWithFormat:@"qianfeng"];
 5         NSLog(@"%p %p %p",str5,str6,str7);
 6         // 判断地址是否相等
 7         if (str5 == str6) {
 8             NSLog(@"相等");
 9         } else {
10             NSLog(@"不相等");
11         }
12         // 判断内容是否相等
13         if ([str5 isEqualToString:str6]) {
14             NSLog(@"相等");
15         } else {
16             NSLog(@"不相等");
17         }
18         

　　5.4 字符串大小比较

　　　　compare方法

 1         NSString * str9 = @"1235";
 2         NSString * str10 = @"124";
 3         // compare
 4         NSComparisonResult result = [str9 compare:str10];
 5         switch (result) {
 6             case NSOrderedAscending:
 7                 NSLog(@"左边<右边");
 8                 break;
 9             case NSOrderedSame:
10                 NSLog(@"左边=右边");
11                 break;
12             case NSOrderedDescending:
13                 NSLog(@"左边>右边");
14                 break;
15             default:
16                 break;