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vector 的数据存在堆中，&vec 获得的只是栈中 vec 的结构的地址，始终不变，而 &vec[0] 是堆中 vector 存储的真正的元素地址，每次动态扩容后都会改变）")]),t._v(" "),s("p",[t._v("好我们回到 Rust。")]),t._v(" "),s("p",[s("strong",[t._v("遍历 vector")])]),t._v(" "),s("div",{staticClass:"language-rust extra-class"},[s("pre",{pre:!0,attrs:{class:"language-rust"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("fn")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function-definition function"}},[t._v("test03")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("let")]),t._v(" v "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token macro property"}},[t._v("vec!")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),s("span",{pre:!0,attrs:{class:"token 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的标准库还包含了很多其它的字符串类型，例如：OsString，OsStr、CString、CStr")]),t._v(" "),s("ul",[s("li",[t._v("String vs Str 后缀：拥有或借用的变体")]),t._v(" "),s("li",[t._v("可存储不同编码的文本或在内存中以不同的形式展现")]),t._v(" "),s("li",[t._v("Library crate 针对存储字符串可提供更多的选项")])]),t._v(" "),s("h3",{attrs:{id:"_2-1-字符串的创建"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2-1-字符串的创建"}},[t._v("#")]),t._v(" 2.1 字符串的创建")]),t._v(" "),s("ul",[s("li",[t._v("很多 "),s("code",[t._v("Vec<T>")]),t._v(" 都可用于 "),s("code",[t._v("String")])]),t._v(" "),s("li",[t._v("利用 "),s("code",[t._v("String::new()")]),t._v(" 创建字符串")]),t._v(" "),s("li",[t._v("使用初始值来创建 String：\n"),s("ul",[s("li",[s("code",[t._v("to_string()")]),t._v(" "),s("strong",[t._v("方法")]),t._v("，可用于实现了 Display trait 的类型，包括字符串字面值")]),t._v(" "),s("li",[s("code",[t._v("String::from()")]),t._v(" "),s("strong",[t._v("函数")]),t._v("，从字面值创建 String 类型")])])])]),t._v(" "),s("div",{staticClass:"language-rust 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"),s("span",{pre:!0,attrs:{class:"token macro property"}},[t._v("println!")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"{}"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" s1"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),s("span",{pre:!0,attrs:{class:"token macro property"}},[t._v("println!")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"{}"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" s2"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])])]),s("p",[t._v("上述例子中，我们发现 "),s("code",[t._v("s1")]),t._v(" 不能再使用了，而 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"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// let s3 = s1 + "-" + &s2 + "-" + &s3;')]),t._v("\n "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// println!("{}", s3);')]),t._v("\n\n "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("let")]),t._v(" res "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token macro property"}},[t._v("format!")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"{}-{}-{}"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" s1"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" s2"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" s3"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n "),s("span",{pre:!0,attrs:{class:"token macro property"}},[t._v("println!")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"{}"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" res"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])])]),s("p",[t._v("上述例子中将三个字符串之间用 "),s("code",[t._v("-")]),t._v(" 连接，如果代码太多显得很繁琐，采用 "),s("code",[t._v("format!")]),t._v(" 宏不仅可以使得代码简单易读，更重要的是不会取得所有变量的所有权。这个宏和 "),s("code",[t._v("println!")]),t._v(" 很像，只不过 "),s("code",[t._v("format!")]),t._v(" 宏是将结果返回，这里可以用一个变量去接收。")]),t._v(" "),s("h3",{attrs:{id:"_2-3-字符串的索引"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2-3-字符串的索引"}},[t._v("#")]),t._v(" 2.3 字符串的索引")]),t._v(" "),s("p",[t._v("不可以按照索引的语法对 String 某部分进行访问，因为 String 类型没有实现 "),s("code",[t._v("Index<Integer>")]),t._v(" trait，例如：")]),t._v(" "),s("div",{staticClass:"language-rust extra-class"},[s("pre",{pre:!0,attrs:{class:"language-rust"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("fn")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function-definition function"}},[t._v("test")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("let")]),t._v(" s "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("String")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("::")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("from")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Hello"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("let")]),t._v(" s1 "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" s"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//这样是错误的")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])])]),s("p",[t._v("之所以无法通过索引进行访问是因为，字符串是用 UTF-8 进行编码，每一个字符都对应一个 Unicode 编码。在英文中，一个字符是 "),s("code",[t._v("1B")]),t._v("，而对于某些语言，一个字符可能对应 "),s("code",[t._v("2B")]),t._v("，而中文一个字符对应 "),s("code",[t._v("3B")]),t._v("，因此用索引进行访问的话，无法知道应该取一个字节还是两个字节。")]),t._v(" "),s("p",[t._v("当然 Rust 不允许通过索引进行访问的另一个原因是，索引操作理应只消耗 "),s("code",[t._v("O(1)")]),t._v(" 的时间，但是为了保证不会越界，需要使用 "),s("code",[t._v("O(n)")]),t._v(" 的时间进行遍历字符串长度。")]),t._v(" "),s("p",[s("strong",[t._v("String 内部表示")])]),t._v(" "),s("p",[t._v("String 实际上是对 "),s("code",[t._v("Vec<u8>")]),t._v(" 进行的包装，可以用 "),s("code",[t._v("len()")]),t._v(" 方法获得字符串长度")]),t._v(" "),s("p",[t._v("字节（Bytes），标量值（Scalar Values），字形簇（Grapheme Clusters）")]),t._v(" "),s("p",[t._v("Rust有三种看待字符串的方式：")]),t._v(" "),s("ul",[s("li",[t._v("字节")]),t._v(" "),s("li",[t._v("标量值")]),t._v(" "),s("li",[t._v("字形簇（最接近所谓的“字母”）")])]),t._v(" "),s("h3",{attrs:{id:"_2-4-切割-string"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2-4-切割-string"}},[t._v("#")]),t._v(" 2.4 切割 String")]),t._v(" "),s("p",[t._v("可以使用 "),s("code",[t._v("[]")]),t._v(" 和 "),s("code",[t._v("一个范围")]),t._v(" 来创建一个字符串的切片")]),t._v(" "),s("ul",[s("li",[t._v("要谨慎使用")]),t._v(" "),s("li",[t._v("如果切割时越过边界就会 panic")])]),t._v(" "),s("div",{staticClass:"language-rust extra-class"},[s("pre",{pre:!0,attrs:{class:"language-rust"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("fn")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function-definition function"}},[t._v("test05")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("let")]),t._v(" hello "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("String")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("::")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("from")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"你好吗"')]),s("span",{pre:!0,attrs:{class:"token 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s"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])])]),s("p",[t._v("上面我们说了在 Rust 中一个中文字符占 "),s("code",[t._v("3B")]),t._v("，因此我们获取字符串 hello 的前 3 个字节，输出结果为 "),s("code",[t._v("你")]),t._v("，但是要注意的是，所获取的字节必须能够构成所定义的字符，比如只获取前两字节最后运行就会报错（但是编译不会报错）。")]),t._v(" "),s("h3",{attrs:{id:"_2-5-遍历-string"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2-5-遍历-string"}},[t._v("#")]),t._v(" 2.5 遍历 String")]),t._v(" "),s("ul",[s("li",[t._v("对于标量值：chars() 方法")]),t._v(" "),s("li",[t._v("对于字节：bytes() 方法")]),t._v(" "),s("li",[t._v("对于字形簇，过于复杂，标准库未提供")])]),t._v(" "),s("div",{staticClass:"language-rust extra-class"},[s("pre",{pre:!0,attrs:{class:"language-rust"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("fn")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function-definition 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"),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("151")]),t._v("\n")])])]),s("p",[s("strong",[t._v("String不简单")])]),t._v(" "),s("ul",[s("li",[t._v("Rust 选择将正确处理 String 数据作为所有 Rust 程序的默认行为——程序员必须在处理 UTF-8 数据之前投入更多的精力")]),t._v(" "),s("li",[t._v("可防止在开发后期处理涉及非 ASCII 字符的错误")])]),t._v(" "),s("h3",{attrs:{id:"各种类型的编码"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#各种类型的编码"}},[t._v("#")]),t._v(" 各种类型的编码")]),t._v(" "),s("ul",[s("li",[t._v("1967 年 ASCII，包含英文字母，阿拉伯数字，西文字符和控制字符")]),t._v(" "),s("li",[t._v("1980 年 GB2312，包含简体中文，拉丁字母和日文假名")]),t._v(" "),s("li",[t._v("1984 年 BIG5，增加了繁体字")]),t._v(" "),s("li",[t._v("1993 年 GB130001，包含了中日韩三国文字")]),t._v(" "),s("li",[t._v("1995 年 GBK，不支持韩文")]),t._v(" "),s("li",[t._v("2000 年 GB18030，兼容更多的字符")])]),t._v(" "),s("p",[t._v("在 1994 年诞生的 Unicode 实现了编码的全球化。")]),t._v(" "),s("p",[t._v("那么这时候如何表示字符呢，英文所需要表示的二进制位和汉字所要表示的二进制位肯定是不同的，也就是说一个英文字符可能要占 1B，而汉字要占 2B，编码时都是将二进制连接在一起，那么怎么知道当前的一个字节所要表示的是英文还是中文呢？因此直接将每个字符用编号表示无法正确区分每个字符的边界。")]),t._v(" "),s("p",[t._v("一种解决方法是 "),s("strong",[t._v("定长编码")]),t._v("，即每个字符都用统一长度表示，位数不够前面补 0。但是这样又出现了一个问题，一个英文字母要占两个字节，要忍受前面全是 0 的情况，只会占用更多的内存。")]),t._v(" "),s("p",[s("img",{attrs:{src:"https://raw.githubusercontent.com/CherryYang05/PicGo-image/master/images/20220519005429.png",alt:"定长编码"}})]),t._v(" "),s("p",[t._v("解决方法也很简单，可以采用 "),s("strong",[t._v("变长编码")]),t._v("，那么如何区分字符边界呢？其实和计组中的 "),s("strong",[t._v("拓展操作码")]),t._v("，"),s("strong",[t._v("IP 地址")]),t._v("，"),s("strong",[t._v("哈夫曼编码")]),t._v(" 都很类似，如下图所示：")]),t._v(" "),s("p",[s("img",{attrs:{src:"https://raw.githubusercontent.com/CherryYang05/PicGo-image/master/images/20220519005820.png",alt:"变长编码"}})]),t._v(" "),s("p",[t._v("这就是 "),s("strong",[t._v("UTF-8 编码")])]),t._v(" "),s("h2",{attrs:{id:"_3-hashmap"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-hashmap"}},[t._v("#")]),t._v(" 3. HashMap")]),t._v(" "),s("p",[t._v("和各种语言中的 HashMap 一样，也是通过键值对来存储数据，通过键（Key）来寻找数据，而不是索引")]),t._v(" "),s("h3",{attrs:{id:"_3-1-创建-hashmap"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-1-创建-hashmap"}},[t._v("#")]),t._v(" 3.1 创建 HashMap")]),t._v(" "),s("ul",[s("li",[t._v("创建空 HashMap：new() 函数")]),t._v(" "),s("li",[t._v("添加数据：insert() 方法")])]),t._v(" "),s("div",{staticClass:"language-rust extra-class"},[s("pre",{pre:!0,attrs:{class:"language-rust"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("use")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token namespace"}},[t._v("std"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("::")]),t._v("collections"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("::")])]),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("HashMap")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("fn")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function-definition function"}},[t._v("main")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("let")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("mut")]),t._v(" hash"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("HashMap")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("String")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("i32")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("HashMap")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("::")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("new")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n hash"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("insert")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("String")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("::")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("from")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Cherry"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("23")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])])]),s("p",[t._v("若声明的时候没有指定类型，则必须要插入数据才不会报错，若声明时已经指定类型了，那么不用插入数据也不会报错。")]),t._v(" "),s("ul",[s("li",[t._v("HashMap 用的较少，不在 Prelude中")]),t._v(" "),s("li",[t._v("标准库对其支持较少，没有内置的宏来创建")]),t._v(" "),s("li",[t._v("HashMap 数据存储在 heap 上")]),t._v(" "),s("li",[t._v("同构的。一个 HashMap 中\n"),s("ul",[s("li",[t._v("所有的 K 必须是同一种类型")]),t._v(" "),s("li",[t._v("所有的 V 必须是同一种类型")])])])]),t._v(" "),s("p",[s("strong",[t._v("另一种创建 HashMap 的方式：collect 方法")])]),t._v(" "),s("p",[t._v("在元素类型为 Tuple 的 Vector 上使用 collect 方法，可以组建一个 HashMap")]),t._v(" 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