2022-08-04 06:59:33 +00:00
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2023-06-26 17:30:52 +00:00
< ol class = "chapter" > < li class = "chapter-item expanded affix " > < a href = "../index.html" > Go语言圣经< / a > < / li > < li class = "chapter-item expanded affix " > < a href = "../preface-zh.html" > 译者序< / a > < / li > < li class = "chapter-item expanded affix " > < a href = "../preface.html" > 前言< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1.html" > < strong aria-hidden = "true" > 1.< / strong > 入门< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-01.html" > < strong aria-hidden = "true" > 1.1.< / strong > Hello, World< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-02.html" > < strong aria-hidden = "true" > 1.2.< / strong > 命令行参数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-03.html" > < strong aria-hidden = "true" > 1.3.< / strong > 查找重复的行< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-04.html" > < strong aria-hidden = "true" > 1.4.< / strong > GIF动画< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-05.html" > < strong aria-hidden = "true" > 1.5.< / strong > 获取URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-06.html" > < strong aria-hidden = "true" > 1.6.< / strong > 并发获取多个URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-07.html" > < strong aria-hidden = "true" > 1.7.< / strong > Web服务< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-08.html" > < strong aria-hidden = "true" > 1.8.< / strong > 本章要点< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2.html" > < strong aria-hidden = "true" > 2.< / strong > 程序结构< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-01.html" > < strong aria-hidden = "true" > 2.1.< / strong > 命名< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-02.html" > < strong aria-hidden = "true" > 2.2.< / strong > 声明< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-03.html" > < strong aria-hidden = "true" > 2.3.< / strong > 变量< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-04.html" > < strong aria-hidden = "true" > 2.4.< / strong > 赋值< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-05.html" > < strong aria-hidden = "true" > 2.5.< / strong > 类型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-06.html" > < strong aria-hidden = "true" > 2.6.< / strong > 包和文件< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-07.html" > < strong aria-hidden = "true" > 2.7.< / strong > 作用域< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3.html" > < strong aria-hidden = "true" > 3.< / strong > 基础数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-01.html" > < strong aria-hidden = "true" > 3.1.< / strong > 整型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-02.html" > < strong aria-hidden = "true" > 3.2.< / strong > 浮点数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-03.html" > < strong aria-hidden = "true" > 3.3.< / strong > 复数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-04.html" > < strong aria-hidden = "true" > 3.4.< / strong > 布尔型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-05.html" class = "active" > < strong aria-hidden = "true" > 3.5.< / strong > 字符串< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-06.html" > < strong aria-hidden = "true" > 3.6.< / strong > 常量< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4.html" > < strong aria-hidden = "true" > 4.< / strong > 复合数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-01.html" > < strong aria-hidden = "true" > 4.1.< / strong > 数组< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-02.html" > < strong aria-hidden = "true" > 4.2.< / strong > Slice< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-03.html" > < strong aria-hidden = "true" > 4.3.< / strong > Map< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-04.html" > < strong aria-hidden = "true" > 4.4.< / strong > 结构体< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-05.html" > < strong aria-hidden = "true" > 4.5.<
2022-08-04 06:59:33 +00:00
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2023-06-26 17:46:27 +00:00
< li > < em > 凹语言(专为 WebAssembly 设计): < a href = "https://github.com/wa-lang/wa" > https://github.com/wa-lang/wa< / a > < / em > < / li >
< li > < em > KCL 配置语言(Rust): < a href = "https://github.com/kcl-lang/kcl" > https://github.com/kcl-lang/kcl< / a > < / em > < / li >
< / ul >
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< hr >
< h2 id = "35-字符串" > < a class = "header" href = "#35-字符串" > 3.5. 字符串< / a > < / h2 >
< p > 一个字符串是一个不可改变的字节序列。字符串可以包含任意的数据， ， （ ） ， < / p >
< p > 内置的len函数可以返回一个字符串中的字节数目（ ） ， ， < len(s)条件约束。< / p >
< pre > < code class = "language-Go" > s := " hello, world"
fmt.Println(len(s)) // " 12"
fmt.Println(s[0], s[7]) // " 104 119" ('h' and 'w')
< / code > < / pre >
< p > 如果试图访问超出字符串索引范围的字节将会导致panic异常： < / p >
< pre > < code class = "language-Go" > c := s[len(s)] // panic: index out of range
< / code > < / pre >
< p > 第i个字节并不一定是字符串的第i个字符， < / p >
< p > 子字符串操作s[i:j]基于原始的s字符串的第i个字节开始到第j个字节（ ） < / p >
< pre > < code class = "language-Go" > fmt.Println(s[0:5]) // " hello"
< / code > < / pre >
< p > 同样， < / p >
< p > 不管i还是j都可能被忽略， ， < / p >
< pre > < code class = "language-Go" > fmt.Println(s[:5]) // " hello"
fmt.Println(s[7:]) // " world"
fmt.Println(s[:]) // " hello, world"
< / code > < / pre >
< p > 其中+操作符将两个字符串连接构造一个新字符串：< / p >
< pre > < code class = "language-Go" > fmt.Println(" goodbye" + s[5:]) // " goodbye, world"
< / code > < / pre >
< p > 字符串可以用==和< 进行比较；比较通过逐个字节比较完成的，因此比较的结果是字符串自然编码的顺序。< / p >
< p > 字符串的值是不可变的：一个字符串包含的字节序列永远不会被改变，当然我们也可以给一个字符串变量分配一个新字符串值。可以像下面这样将一个字符串追加到另一个字符串：< / p >
< pre > < code class = "language-Go" > s := " left foot"
t := s
s += " , right foot"
< / code > < / pre >
< p > 这并不会导致原始的字符串值被改变， ， < / p >
< pre > < code class = "language-Go" > fmt.Println(s) // " left foot, right foot"
fmt.Println(t) // " left foot"
< / code > < / pre >
< p > 因为字符串是不可修改的，因此尝试修改字符串内部数据的操作也是被禁止的：< / p >
< pre > < code class = "language-Go" > s[0] = 'L' // compile error: cannot assign to s[0]
< / code > < / pre >
< p > 不变性意味着如果两个字符串共享相同的底层数据的话也是安全的， ， < / p >
< h3 id = "351-字符串面值" > < a class = "header" href = "#351-字符串面值" > 3.5.1. 字符串面值< / a > < / h3 >
< p > 字符串值也可以用字符串面值方式编写，只要将一系列字节序列包含在双引号内即可：< / p >
2022-10-06 07:01:25 +00:00
< pre > < code > " Hello, world"
2022-08-04 06:59:33 +00:00
< / code > < / pre >
< p > < img src = "../images/ch3-04.png" alt = "" / > < / p >
< p > 因为Go语言源文件总是用UTF8编码， ， < / p >
< p > 在一个双引号包含的字符串面值中，可以用以反斜杠< code > \< / code > 开头的转义序列插入任意的数据。下面的换行、回车和制表符等是常见的ASCII控制代码的转义方式： < / p >
< pre > < code > \a 响铃
\b 退格
\f 换页
\n 换行
\r 回车
\t 制表符
\v 垂直制表符
\' 单引号（只用在 '\'' 形式的rune符号面值中）
\" 双引号（只用在 " ..." 形式的字符串面值中）
\\ 反斜杠
< / code > < / pre >
< p > 可以通过十六进制或八进制转义在字符串面值中包含任意的字节。一个十六进制的转义形式是< code > \xhh< / code > ， （ ） < code > \ooo< / code > ， （ ） ， < code > \377< / code > （ ： ， ） < / p >
< p > 一个原生的字符串面值形式是`...`，使用反引号代替双引号。在原生的字符串面值中，没有转义操作；全部的内容都是字面的意思，包含退格和换行，因此一个程序中的原生字符串面值可能跨越多行（译注：在原生字符串面值内部是无法直接写`字符的，可以用八进制或十六进制转义或+" `" 连接字符串常量完成） ， （ ： ） < / p >
< p > 原生字符串面值用于编写正则表达式会很方便， < / p >
< pre > < code class = "language-Go" > const GoUsage = `Go is a tool for managing Go source code.
Usage:
go command [arguments]
...`
< / code > < / pre >
< h3 id = "352-unicode" > < a class = "header" href = "#352-unicode" > 3.5.2. Unicode< / a > < / h3 >
< p > 在很久以前， ， ： ， ， ： ， ， ， （ ： ） ？ < / p >
< p > 答案就是使用Unicode（ ） ， ， ， ， ， ， （ ： ） < / p >
< p > 在第八版本的Unicode标准里收集了超过120,000个字符， ？ ， ； < / p >
< p > 我们可以将一个符文序列表示为一个int32序列。这种编码方式叫UTF-32或UCS-4， ， ， ， ， ， ？ < / p >
< h3 id = "353-utf-8" > < a class = "header" href = "#353-utf-8" > 3.5.3. UTF-8< / a > < / h3 >
< p > UTF8是一个将Unicode码点编码为字节序列的变长编码。UTF8编码是由Go语言之父Ken Thompson和Rob Pike共同发明的， ， ， ， ， ， ， ； < / p >
< pre > < code > 0xxxxxxx runes 0-127 (ASCII)
110xxxxx 10xxxxxx 128-2047 (values < 128 unused)
1110xxxx 10xxxxxx 10xxxxxx 2048-65535 (values < 2048 unused)
11110xxx 10xxxxxx 10xxxxxx 10xxxxxx 65536-0x10ffff (other values unused)
< / code > < / pre >
< p > 变长的编码无法直接通过索引来访问第n个字符， ， ， ： ， （ ： ， ） ， ， ， ， ， < / p >
< p > Go语言的源文件采用UTF8编码， （ ， ） ， < / p >
< p > 有很多Unicode字符很难直接从键盘输入， ； （ ： ） ： < code > \uhhhh< / code > 对应16bit的码点值， < code > \Uhhhhhhhh< / code > 对应32bit的码点值， ； ： ： < / p >
< pre > < code > " 世界"
" \xe4\xb8\x96\xe7\x95\x8c"
" \u4e16\u754c"
" \U00004e16\U0000754c"
< / code > < / pre >
< p > 上面三个转义序列都为第一个字符串提供替代写法，但是它们的值都是相同的。< / p >
< p > Unicode转义也可以使用在rune字符中。下面三个字符是等价的： < / p >
< pre > < code > '世' '\u4e16' '\U00004e16'
< / code > < / pre >
< p > 对于小于256的码点值可以写在一个十六进制转义字节中， < code > \x41< / code > 对应字符'A'，但是对于更大的码点则必须使用< code > \u< / code > 或< code > \U< / code > 转义形式。因此，< code > \xe4\xb8\x96< / code > 并不是一个合法的rune字符， < / p >
< p > 得益于UTF8编码优良的设计， ： < / p >
< pre > < code class = "language-Go" > func HasPrefix(s, prefix string) bool {
return len(s) > = len(prefix) & & s[:len(prefix)] == prefix
}
< / code > < / pre >
< p > 或者是后缀测试：< / p >
< pre > < code class = "language-Go" > func HasSuffix(s, suffix string) bool {
return len(s) > = len(suffix) & & s[len(s)-len(suffix):] == suffix
}
< / code > < / pre >
< p > 或者是包含子串测试：< / p >
< pre > < code class = "language-Go" > func Contains(s, substr string) bool {
for i := 0; i < len(s); i++ {
if HasPrefix(s[i:], substr) {
return true
}
}
return false
}
< / code > < / pre >
< p > 对于UTF8编码后文本的处理和原始的字节处理逻辑是一样的。但是对应很多其它编码则并不是这样的。（ ， < / p >
< p > 另一方面， ， ， ， ， ： < / p >
< pre > < code class = "language-Go" > import " unicode/utf8"
s := " Hello, 世界"
fmt.Println(len(s)) // " 13"
fmt.Println(utf8.RuneCountInString(s)) // " 9"
< / code > < / pre >
< p > 为了处理这些真实的字符， ， ： < / p >
< pre > < code class = "language-Go" > for i := 0; i < len(s); {
r, size := utf8.DecodeRuneInString(s[i:])
fmt.Printf(" %d\t%c\n" , i, r)
i += size
}
< / code > < / pre >
< p > 每一次调用DecodeRuneInString函数都返回一个r和长度， ， ， ， ， ； ， < / p >
< p > < img src = "../images/ch3-05.png" alt = "" / > < / p >
< pre > < code class = "language-Go" > for i, r := range " Hello, 世界" {
fmt.Printf(" %d\t%q\t%d\n" , i, r, r)
}
< / code > < / pre >
< p > 我们可以使用一个简单的循环来统计字符串中字符的数目，像这样：< / p >
< pre > < code class = "language-Go" > n := 0
for _, _ = range s {
n++
}
< / code > < / pre >
< p > 像其它形式的循环那样，我们也可以忽略不需要的变量：< / p >
< pre > < code class = "language-Go" > n := 0
for range s {
n++
}
< / code > < / pre >
< p > 或者我们可以直接调用utf8.RuneCountInString(s)函数。< / p >
< p > 正如我们前面提到的， ， ， ， ， ？ < / p >
< p > 每一个UTF8字符解码， ， ， < code > \uFFFD< / code > ，在印刷中这个符号通常是一个黑色六角或钻石形状，里面包含一个白色的问号" ?" 。当程序遇到这样的一个字符， ， < / p >
< p > UTF8字符串作为交换格式是非常方便的， ， ， < / p >
< p > 将[]rune类型转换应用到UTF8编码的字符串， ： < / p >
< pre > < code class = "language-Go" > // " program" in Japanese katakana
s := " プログラム"
fmt.Printf(" % x\n" , s) // " e3 83 97 e3 83 ad e3 82 b0 e3 83 a9 e3 83 a0"
r := []rune(s)
fmt.Printf(" %x\n" , r) // " [30d7 30ed 30b0 30e9 30e0]"
< / code > < / pre >
< p > （ < code > % x< / code > 参数用于在每个十六进制数字前插入一个空格。）< / p >
< p > 如果是将一个[]rune类型的Unicode字符slice或数组转为string， ： < / p >
< pre > < code class = "language-Go" > fmt.Println(string(r)) // " プログラム"
< / code > < / pre >
< p > 将一个整数转型为字符串意思是生成以只包含对应Unicode码点字符的UTF8字符串： < / p >
< pre > < code class = "language-Go" > fmt.Println(string(65)) // " A" , not " 65"
fmt.Println(string(0x4eac)) // " 京"
< / code > < / pre >
< p > 如果对应码点的字符是无效的，则用< code > \uFFFD< / code > 无效字符作为替换：< / p >
< pre > < code class = "language-Go" > fmt.Println(string(1234567)) // " ?"
< / code > < / pre >
< h3 id = "354-字符串和byte切片" > < a class = "header" href = "#354-字符串和byte切片" > 3.5.4. 字符串和Byte切片< / a > < / h3 >
< p > 标准库中有四个包对字符串处理尤为重要： < / p >
< p > bytes包也提供了很多类似功能的函数， ， ， ， < / p >
< p > strconv包提供了布尔型、整型数、浮点数和对应字符串的相互转换， < / p >
< p > unicode包提供了IsDigit、IsLetter、IsUpper和IsLower等类似功能， ， ， ， ， < / p >
< p > 下面例子的basename函数灵感源于Unix shell的同名工具。在我们实现的版本中， < / p >
< pre > < code class = "language-Go" > fmt.Println(basename(" a/b/c.go" )) // " c"
fmt.Println(basename(" c.d.go" )) // " c.d"
fmt.Println(basename(" abc" )) // " abc"
< / code > < / pre >
< p > 第一个版本并没有使用任何库，全部手工硬编码实现：< / p >
< p > < u > < i > gopl.io/ch3/basename1< / i > < / u > < / p >
< pre > < code class = "language-Go" > // basename removes directory components and a .suffix.
// e.g., a => a, a.go => a, a/b/c.go => c, a/b.c.go => b.c
func basename(s string) string {
// Discard last '/' and everything before.
for i := len(s) - 1; i > = 0; i-- {
if s[i] == '/' {
s = s[i+1:]
break
}
}
// Preserve everything before last '.'.
for i := len(s) - 1; i > = 0; i-- {
if s[i] == '.' {
s = s[:i]
break
}
}
return s
}
< / code > < / pre >
< p > 这个简化版本使用了strings.LastIndex库函数： < / p >
< p > < u > < i > gopl.io/ch3/basename2< / i > < / u > < / p >
< pre > < code class = "language-Go" > func basename(s string) string {
slash := strings.LastIndex(s, " /" ) // -1 if " /" not found
s = s[slash+1:]
if dot := strings.LastIndex(s, " ." ); dot > = 0 {
s = s[:dot]
}
return s
}
< / code > < / pre >
< p > path和path/filepath包提供了关于文件路径名更一般的函数操作。使用斜杠分隔路径可以在任何操作系统上工作。斜杠本身不应该用于文件名， ， ， ， ， < code > c:\foo\bar< / code > 等。< / p >
< p > 让我们继续另一个字符串的例子。函数的功能是将一个表示整数值的字符串， ， ； < / p >
< p > < u > < i > gopl.io/ch3/comma< / i > < / u > < / p >
< pre > < code class = "language-Go" > // comma inserts commas in a non-negative decimal integer string.
func comma(s string) string {
n := len(s)
if n < = 3 {
return s
}
return comma(s[:n-3]) + " ," + s[n-3:]
}
< / code > < / pre >
< p > 输入comma函数的参数是一个字符串。如果输入字符串的长度小于或等于3的话， ， ， < / p >
< p > 一个字符串是包含只读字节的数组， ， ， < / p >
< p > 字符串和字节slice之间可以相互转换： < / p >
< pre > < code class = "language-Go" > s := " abc"
b := []byte(s)
s2 := string(b)
< / code > < / pre >
< p > 从概念上讲，一个[]byte(s)转换是分配了一个新的字节数组用于保存字符串数据的拷贝， ， ， ， < / p >
< p > 为了避免转换中不必要的内存分配， ： < / p >
< pre > < code class = "language-Go" > func Contains(s, substr string) bool
func Count(s, sep string) int
func Fields(s string) []string
func HasPrefix(s, prefix string) bool
func Index(s, sep string) int
func Join(a []string, sep string) string
< / code > < / pre >
< p > bytes包中也对应的六个函数： < / p >
< pre > < code class = "language-Go" > func Contains(b, subslice []byte) bool
func Count(s, sep []byte) int
func Fields(s []byte) [][]byte
func HasPrefix(s, prefix []byte) bool
func Index(s, sep []byte) int
func Join(s [][]byte, sep []byte) []byte
< / code > < / pre >
< p > 它们之间唯一的区别是字符串类型参数被替换成了字节slice类型的参数。< / p >
< p > bytes包还提供了Buffer类型用于字节slice的缓存。一个Buffer开始是空的， ， ， ： < / p >
< p > < u > < i > gopl.io/ch3/printints< / i > < / u > < / p >
< pre > < code class = "language-Go" > // intsToString is like fmt.Sprint(values) but adds commas.
func intsToString(values []int) string {
var buf bytes.Buffer
buf.WriteByte('[')
for i, v := range values {
if i > 0 {
buf.WriteString(" , " )
}
fmt.Fprintf(& buf, " %d" , v)
}
buf.WriteByte(']')
return buf.String()
}
func main() {
fmt.Println(intsToString([]int{1, 2, 3})) // " [1, 2, 3]"
}
< / code > < / pre >
< p > 当向bytes.Buffer添加任意字符的UTF8编码时， ， < / p >
< p > bytes.Buffer类型有着很多实用的功能， ， ， ， < / p >
< p > < strong > 练习 3.10： < / strong > 编写一个非递归版本的comma函数， < / p >
< p > < strong > 练习 3.11： < / strong > 完善comma函数， < / p >
< p > < strong > 练习 3.12： < / strong > 编写一个函数，判断两个字符串是否是相互打乱的，也就是说它们有着相同的字符，但是对应不同的顺序。< / p >
< h3 id = "355-字符串和数字的转换" > < a class = "header" href = "#355-字符串和数字的转换" > 3.5.5. 字符串和数字的转换< / a > < / h3 >
< p > 除了字符串、字符、字节之间的转换， < / p >
< p > 将一个整数转为字符串， ； ： < / p >
< pre > < code class = "language-Go" > x := 123
y := fmt.Sprintf(" %d" , x)
fmt.Println(y, strconv.Itoa(x)) // " 123 123"
< / code > < / pre >
< p > FormatInt和FormatUint函数可以用不同的进制来格式化数字： < / p >
< pre > < code class = "language-Go" > fmt.Println(strconv.FormatInt(int64(x), 2)) // " 1111011"
< / code > < / pre >
< p > fmt.Printf函数的%b、%d、%o和%x等参数提供功能往往比strconv包的Format函数方便很多， ： < / p >
< pre > < code class = "language-Go" > s := fmt.Sprintf(" x=%b" , x) // " x=1111011"
< / code > < / pre >
< p > 如果要将一个字符串解析为整数， ， ： < / p >
< pre > < code class = "language-Go" > x, err := strconv.Atoi(" 123" ) // x is an int
y, err := strconv.ParseInt(" 123" , 10, 64) // base 10, up to 64 bits
< / code > < / pre >
< p > ParseInt函数的第三个参数是用于指定整型数的大小； ， ， ， < / p >
< p > 有时候也会使用fmt.Scanf来解析输入的字符串和数字， ， < / p >
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