#字符串学习总结

##1. 创建

//构造方法
NSString *s1 = [[NSString alloc] initWithFormat:@"%@ 真简单", @"iOS开发"];
//类方法
NSString *s2 = [NSString stringWithFormat:@"%@ 好简单啊", @"OC"];
// 将 C 语言字符串转换成 OC 字符串
NSString *s3 = [[NSString alloc] initWithUTF8String:"hello iOS"];
//从文件读取
NSString *file = [[NSString alloc] initWithContentsOfFile:@"/Users/apple/Desktop/Launchable.h" encoding:NSUTF8StringEncoding error:nil];
//从url读取
NSString *html = [[NSString alloc] initWithContentsOfURL:[NSURL URLWithString:@"http://www.youdao.com"] encoding:NSUTF8StringEncoding error:nil];

##2. 查看
//1. 比较
BOOL isEqual = [@”123” isEqualToString:@”123”];
//下面这个方法可以根据options进行排序,常见的有按数字排序(options:NSNumericSearch),
//有按照字符串排序, 还可以根据正则表达式排序
NSComparisonResult result = [@”123” compare:@”124” options:NSNumericSearch]);

//2. 判断字符串的前后缀, 返回值均为bool类型
[@"123.txt" hasSuffix:@".txt"]
[@"http://www.baidu.com hasPrefix:@"http://"]

//3. 根据range取字符串
//3.1 从字符串中获得子字符串的range
 NSRange range = [@"abcdefgcdefg"; rangeOfString:@"acd"];
 //可以通过判断range.location 判断有没有找到
 if(range.location == NSNotFound) {
     NSLog(@"没有找到");
 }


 //3.2下面是一个例子寻找字符串中所有包含子字符串的位置和长度, 
   str = @"123abcd456defg123ab45qw";


    NSRange range = NSMakeRange(0, 0);
    do {
        NSUInteger loc = range.location + range.length;
        NSUInteger len = str.length - loc;
        range = [str rangeOfString:@"3a" options:1 range:NSMakeRange(loc, len)];

        if (range.location != NSNotFound) {
            NSLog(@"%@", NSStringFromRange(range));
        }
    } while (range.location != NSNotFound);

  //4. 获取子字符串
  // 子字符串 substring
    NSString *str = @"0123456789";
    NSString *s1 = [str substringFromIndex:5];
    NSLog(@"%@", s1);
    NSString *s2 = [str substringToIndex:5];
    NSLog(@"%@", s2);
    // 在科学计算中有一个习惯, 表示范围的时候, 左边取得到, 右边取不到
    // arc4random_uniform(10)
    // 左闭右开区间
    NSRange range = NSMakeRange(3, 3);
    NSString *s3 = [str substringWithRange:range];
    NSLog(@"%@", s3);

//5. 通过正则匹配字符串
// 正则表达式, regular expression
    // [^字符] 含义是非该字符的字符
    // [^<] 不是 < 的任意字符
    // + 放在通配符的后面, 表示多个的意思
    // [^<]+ 就是任意多个不由<组合而来的字符串
    NSString *mark = @"<sapn style\"color:red\">1234567890987654321qazwsxedc</span>";
    NSRange range = [mark rangeOfString:@">[^<]+<" options:1024];
    range = NSMakeRange(range.location + 1, range.length - 2);
    NSString *res = [mark substringWithRange:range];
    NSLog(@"%@", res);

 //6. 其他用法
 //去掉首尾空格
 NSString *str1 = @"   admin    ";
    NSLog(@"|%@|", str1);
    str1 = [str1 stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
    NSLog(@"|%@|", str1);
   //去掉收尾大写 
    NSString *str2 = @"ABCadminDEF";
    NSLog(@"|%@|", str2);
    str2 = [str2 stringByTrimmingCharactersInSet:[NSCharacterSet uppercaseLetterCharacterSet]];
    NSLog(@"|%@|", str2);
    去掉首尾小写
    NSString *str3 = @"abcADMINdefg";
    NSLog(@"|%@|", str3);
    str3 = [str3 stringByTrimmingCharactersInSet:[NSCharacterSet lowercaseLetterCharacterSet]];
    NSLog(@"|%@|", str3);
    //去掉/
    NSString *path = @"/Users/apple/Destop/";
    path = [path stringByTrimmingCharactersInSet:[NSCharacterSet characterSetWithCharactersInString:@"/"]];
    NSLog(@"path = %@", path);