OC语法--NSString对象

1.创建NSString对象

void stringCreate() {
    //这种方式创建，不需要释放内存
    NSString *str1 = @"A String";//
    //
    NSString *str2 = [[NSString alloc] init];
    str2 = @"B String";
    [str2 release];

    NSString *str3 = [[NSString alloc]initWithString:@"C string!"];
    [str3 release];

    //静态方法创建对象，不需要管理内存
    str3 = [NSString stringWithString:@"c string!"];

    NSString *str4 = [[NSString alloc] initWithUTF8String:"D string!"];
    [str4 release];

    NSString *str5 = [[NSString alloc] initWithFormat:
                      @"my age is %i and height is %.2f",28,1.65f];
    NSLog(@"str5:%@",str5);
    [str5 release];
}

2.NSString的导入与导出：从文件或url读取内容，以及写文件

void stringCreate2(){
    NSString *path=@"/Users/luteresa/Desktop/hello.txt";
    //NSString *str1 = [NSString stringWithContentsOfFile:path];
    NSError *perror;
    NSString *str2 = [NSString stringWithContentsOfFile:path encoding:(NSUTF8StringEncoding) error:&perror];
    if (perror) {
        NSLog(@"读取错误：%@",perror);
    } else {
        NSLog(@"%@",str2);
    }
}
void stringCreate3(){
    NSString *path = @"/Users/luteresa/Desktop/abc/abc.txt";

    //NSURL *url = [NSURL URLWithString:@"file:///Users/luteresa/Desktop/abc.txt"];
// NSURL *url = [NSURL URLWithString:@""];
// NSString *str2 = [NSString stringWithContentsOfURL: url encoding:NSUTF8StringEncoding error:nil];
// //NSLog(@"%@",str2);
    NSString *str = @"123456";
    NSError *perror;
    //[perror localizedDescription];
    [str writeToFile:path atomically:YES encoding:NSUTF8StringEncoding error:&perror];
    if (perror) {
        NSLog(@"写入失败，%@", [perror localizedDescription]);
    } else {
        NSLog(@"写入成功");
    }
}
void stringToFile(){
    NSString *path = @"/Users/luteresa/Desktop/test.txt";
    NSString *str1 = @"123457890";
    [str1 writeToFile:path atomically:YES encoding:NSUTF8StringEncoding error:nil];
}

3.NSString常用方法：

(1) 大小写处理

(NSString *)lowercaseString;  //全部转为小写字母
(NSString *)capitalizedString;//首字符变大写，其他变小写

(2)字符串比较

void compare() {
    // 检测字符串的内容是否相同
    BOOL result = [@"abc" isEqualToString:@"abc"];
    NSLog(@"%i", result);

    // NSOrderedAscending  右边的字符串比左边大
    // NSOrderedSame  两个字符串的内容相同
    // NSOrderedDescending  左边的字符串比右边的大
    NSComparisonResult result2 = [@"abc" compare:@"Abc"];
    if (result2 == NSOrderedSame) {
        NSLog(@"两个字符串的内容相同");
    } else if (result2 == NSOrderedAscending) {
        NSLog(@"右边 > 左边");
    } else if (result2 == NSOrderedDescending) {
        NSLog(@"右边 < 左边");
    }
}

还有一个忽略大小写的比较方法，用法余compare一样

- (NSComparisonResult)caseInsensitiveCompare:(NSString *)string;

(3) 搜索字符串

void search() {
    NSString *str = @"123456456.txt";

    NSLog(@"是否以22开头：%i", [str hasPrefix:@"22"]);
    NSLog(@"是否以txt结尾：%i", [str hasSuffix:@"txt"]);

    // 搜索字符串
    NSRange range = [str rangeOfString:@"456"];
    // range.length == 0
    if (range.location == NSNotFound) {
        NSLog(@"不能找到");
    } else {
        NSLog(@"找到的范围是：%@", NSStringFromRange(range));
    }

    // 从尾部开始搜索字符串
    range = [str rangeOfString:@"456" options:NSBackwardsSearch];
    NSLog(@"%@", NSStringFromRange(range));

    // 指定范围进行搜索
     range = [str rangeOfString:@"456" options:NSBackwardsSearch range:NSMakeRange(1, 10)];
    NSLog(@"%@", NSStringFromRange(range));}

(4) 字符串截取

void subString() {
    NSString *str = @"123456";

    // 从索引3开始截取到尾部(包括3)
    NSLog(@"%@", [str substringFromIndex:3]);

    // 从头部开始截取到索引3之前(不包括3)
    NSLog(@"%@", [str substringToIndex:3]);

    // 指定范围进行截取
    NSRange range = NSMakeRange(2, 3);
    NSLog(@"%@", [str substringWithRange:range]);

    NSString *str2 = @"a-b-c-d-5";
    NSArray *array = [str2 componentsSeparatedByString:@"-"];
    NSLog(@"%@", array);

    NSString *str3 = [array objectAtIndex:0];
    NSLog(@"%@", str3);
}

(5)#pragma mark 与路径相关

void pathTest() {
    // 快速创建一个自动释放的数组
    NSMutableArray *components = [NSMutableArray array];
    [components addObject:@"Users"];
    [components addObject:@"MJ"];
    [components addObject:@"Desktop"];
    // 将数组中的所有字符串拼接成一个路径
    NSString *path = [NSString pathWithComponents:components];
    NSLog(@"%@", path);

    // 将路径分解成一个数组
    NSArray *cmps = [path pathComponents];
    NSLog(@"%@", cmps);

    // path是一个字符串常量，是不可变的
    path = @"/users/mj/test";
    // 判断是够为绝对路径（依据是前面有无/）
    NSLog(@"%i", [path isAbsolutePath]);
    NSLog(@"最后一个目录：%@", [path lastPathComponent]);
    // 删除最后一个目录
    NSLog(@"%@", [path stringByDeletingLastPathComponent]);
    // 在最后面拼接一个目录
    NSLog(@"%@", [path stringByAppendingPathComponent:@"abc"]);
}

(6）#pragma mark 拓展名处理

void extension() {
    NSString *str = @"/User/MJ/test.txt";

    NSLog(@"拓展名：%@", [str pathExtension]);
    // 删除拓展名
    NSLog(@"%@", [str stringByDeletingPathExtension]);
    // 添加拓展名
    NSLog(@"%@", [@"abc" stringByAppendingPathExtension:@"mp3"]);

 //修改文件名
    NSString *tmp,*str2 = @"/User/leon/hello.txt";
    NSString *extensionName =[str2 pathExtension];
   tmp = [[[[str2 stringByDeletingPathExtension]stringByDeletingLastPathComponent]
      stringByAppendingPathComponent:@"world"]stringByAppendingPathExtension:extensionName];

    NSLog(@"%@",tmp);
}

(7）#pragma mark 其他用法，NSString类与基本类型转换等

void other() {
    NSString *str = @"12";
    int a = [str intValue];
    NSLog(@"%i", a);

    // 计算字数，不是计算字符数
    NSLog(@"length=%zi", [@"我是字符串123" length]);

    // 取出对应的字符
    unichar c = [@"abc" characterAtIndex:0];
    NSLog(@"%c", c);

    // 返回C语言中的字符串
    const char *s = [@"abc" UTF8String];
    NSLog(@"%s", s);
}

NSMutableString：NSString子类，可变字符串

#pragma mark 可变字符串的创建
void stringCreate() {
    // 预先分配10个字数的存储空间
    NSMutableString *str = [[NSMutableString alloc] initWithCapacity:10];
    // 设置字符串内容
    [str setString:@"1234"];

    // 拼接一个字符串
    [str appendString:@"567"];
    // 拼接字符串
    [str appendFormat:@"age is %i and height is %.2f", 27, 1.55f];

    // 替换字符串
    NSRange range = [str rangeOfString:@"height"];
    //NSRange range = NSMakeRange(7, 3);
    [str replaceCharactersInRange:range withString:@"no"];

    // 插入字符串
    [str insertString:@"abc" atIndex:2];

    // 删除字符串
    range = [str rangeOfString:@"age"];
    [str deleteCharactersInRange:range];

    NSLog(@"%@", str);

    // 释放对象
    [str release];
}