Objective-C学习笔记-NSString

1.NSString是OC中用来保存字符串的对象，可以通过在C字符串常量前加上一个@符号来创建一个NSString对象，例如

NSString *strTest=@"my name is xy";

2.也可以使用NSSring的方法来创建，例如，其中stringWithFormat的用法和NSLog一样

        const char* test="my name is xy";
        NSString *strTest=[NSString stringWithFormat:@"%s",test];
        NSString *strTest=[NSString stringWithCString:test encoding:NSASCIIStringEncoding];
        NSString *strTest=[[NSString alloc] initWithCString:test encoding:NSASCIIStringEncoding];

3.NSString也可以转换为一个C字符串，例如

NSLog(@"%s",[strTest cStringUsingEncoding:NSASCIIStringEncoding]);

4.获取NSString字符串长度，注意，这里%zd对应的数字类型是size_t，代表和机器类型相关的unsigned类型，即和NSUInteger一样，这里也可以使用%ld或者%d

NSLog(@"str length is %zd",[strTest length]);

5.两个NSString对象之间比较是否相同，区分大小写，相同则返回true

NSLog(@"str cmp result is %@",[strTest isEqualToString:@"hello world"]?@"true":@"false");

6.不区分大小写比较，相同返回0

NSLog(@"str cmp result is %ld",[strTest compare:@"my name is xY" options:NSCaseInsensitiveSearch]);
NSLog(@"str cmp result is %ld",[strTest caseInsensitiveCompare:@"my name is xY"]);

7.判断NSString是否以某个字符串开头

NSLog(@"str has Prefix %s",[strTest hasPrefix:@"m1"]?"true":"false");

8.判断NSString是否以某个字符串结尾

NSLog(@"str has Suffix %s",[strTest hasSuffix:@"xy"]?"true":"false");

9.字符串查找，下面输出结果为location is 3，len is 4

        NSRange range=[strTest rangeOfString:@"Name" options:NSCaseInsensitiveSearch];
        if (range.location==NSNotFound){
            NSLog(@"not found");
        }else{
            NSLog(@"loaction is %ld,len is %ld",range.location,range.length);
        }

10.从后往前查找

        NSRange range=[strTest rangeOfString:@"Name" options:NSCaseInsensitiveSearch |
                       NSBackwardsSearch];
        if (range.location==NSNotFound){
            NSLog(@"not found");
        }else{
            NSLog(@"loaction is %ld,len is %ld",range.location,range.length);
        }

11.指定范围查找

        NSRange searchRange=NSMakeRange(0, 9);
        NSRange range=[strTest rangeOfString:@"Name" options:NSCaseInsensitiveSearch |
                       NSBackwardsSearch range:searchRange];
        if (range.location==NSNotFound){
            NSLog(@"not found");
        }else{
            NSLog(@"loaction is %ld,len is %ld",range.location,range.length);
        }

12.返回字符串的小写，不会修改原有字符串

NSLog(@"%@",[strTest lowercaseString]);

13.返回字符串的大写，不会修改原有字符串

NSLog(@"%@",[strTest uppercaseString]);

14.返回单词首字母大写的字符串，不会修改原有字符串

NSLog(@"%@",[strTest capitalizedString]);

15.返回指定位置上的字符

NSLog(@"%c",[@"123456" characterAtIndex:0]);

16.字符串转基本类型，例如int，float，double等，值得一提的是，如果字符串格式不正确不会产生异常，而是会返回0或者0.000

NSLog(@"%d",[@"122" intValue]);
NSLog(@"%f",[@"122.3" floatValue]);
NSLog(@"%f",[@"3.14154343" doubleValue]);

17.字符串截取

NSLog(@"%@",[@"123456" substringFromIndex:2]);
NSLog(@"%@",[@"123456" substringToIndex:2]);
NSLog(@"%@",[@"123456" substringWithRange:NSMakeRange(0, 2)]);

18.字符串分割转数组

NSArray *array = [@"1,2,3,4,5,6" componentsSeparatedByString:@","];
NSLog(@"%@",array);

19.字符串数组拼接为路径

NSMutableArray *components = [NSMutableArray array];
[components addObject:@"Users"];
[components addObject:@"CentralPerk"];  
[components addObject:@"Desktop"];
NSString *path = [NSString pathWithComponents:components];
NSLog(@"%@",path);

20.路径分割成字符串数组

NSArray *array = [@"user/xy/music" pathComponents];
NSLog(@"%@",array);

21.判断是否为绝对路径(依据：是否以'/'开始)

NSString *path = @"/Users/CentralPerk/Desktop";
NSLog(@"%i",[path isAbsolutePath]);

22.获取路径中最后一个目录

NSLog(@"%@",[@"user/xy/music" lastPathComponent]);

23.删除路径中最后一个目录，不会影响原有路径

NSString *path=@"user/xy/music";
NSLog(@"%@,%@",[path stringByDeletingLastPathComponent],path);

24.字符串拼接

NSString *path=@"user/xy/music";
NSLog(@"%@",[path stringByAppendingPathComponent:@"111"]);
NSLog(@"%@",[path stringByAppendingString:@"222"]);
NSLog(@"%@",[path stringByAppendingFormat:@"%@%@",@"b",@"c"]);

25.文件扩展名操作，不影响原有字符串

NSString *path=@"user/xy/music/1.mp3";
//获取文件扩展名
NSLog(@"%@",[path pathExtension]);
//添加拓展名,不需要带.
NSLog(@"%@",[path stringByAppendingPathExtension:@"mp3"]);
//删除拓展名,带.一块删除
NSLog(@"%@",[path stringByDeletingPathExtension]);

26.字符串替换

NSString *path=@"user/xy/music/1.mp3";
NSLog(@"%@",[path stringByReplacingOccurrencesOfString:@"xy" withString:@"daxiongmao"]);