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" class = "active" > < 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" > < 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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2022-08-24 10:48:15 +00:00
< li > < em > KusonStack一站式可编程配置技术栈(Go): < a href = "https://github.com/KusionStack/kusion" > https://github.com/KusionStack/kusion< / a > < / em > < / li >
< li > < em > KCL 配置编程语言(Rust): < a href = "https://github.com/KusionStack/KCLVM" > https://github.com/KusionStack/KCLVM< / a > < / em > < / li >
< li > < em > 凹语言™: < a href = "https://github.com/wa-lang/wa" > https://github.com/wa-lang/wa< / a > < / em > < / li >
2022-08-04 06:59:33 +00:00
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< hr >
< h2 id = "31-整型" > < a class = "header" href = "#31-整型" > 3.1. 整型< / a > < / h2 >
< p > Go语言的数值类型包括几种不同大小的整数、浮点数和复数。每种数值类型都决定了对应的大小范围和是否支持正负符号。让我们先从整数类型开始介绍。< / p >
< p > Go语言同时提供了有符号和无符号类型的整数运算。这里有int8、int16、int32和int64四种截然不同大小的有符号整数类型, 分别对应8、16、32、64bit大小的有符号整数, 与此对应的是uint8、uint16、uint32和uint64四种无符号整数类型。< / p >
< p > 这里还有两种一般对应特定CPU平台机器字大小的有符号和无符号整数int和uint; 其中int是应用最广泛的数值类型。这两种类型都有同样的大小, 32或64bit, 但是我们不能对此做任何的假设; 因为不同的编译器即使在相同的硬件平台上可能产生不同的大小。< / p >
< p > Unicode字符rune类型是和int32等价的类型, 通常用于表示一个Unicode码点。这两个名称可以互换使用。同样byte也是uint8类型的等价类型, byte类型一般用于强调数值是一个原始的数据而不是一个小的整数。< / p >
< p > 最后, 还有一种无符号的整数类型uintptr, 没有指定具体的bit大小但是足以容纳指针。uintptr类型只有在底层编程时才需要, 特别是Go语言和C语言函数库或操作系统接口相交互的地方。我们将在第十三章的unsafe包相关部分看到类似的例子。< / p >
< p > 不管它们的具体大小, int、uint和uintptr是不同类型的兄弟类型。其中int和int32也是不同的类型, 即使int的大小也是32bit, 在需要将int当作int32类型的地方需要一个显式的类型转换操作, 反之亦然。< / p >
2022-09-02 12:31:34 +00:00
< p > 其中有符号整数采用2的补码形式表示, 也就是最高bit位用来表示符号位, 一个n-bit的有符号数的值域是从-2< sup > n-1< / sup > 到2< sup > n-1< / sup > -1。无符号整数的所有bit位都用于表示非负数, 值域是0到2< sup > n< / sup > -1。例如, int8类型整数的值域是从-128到127, 而uint8类型整数的值域是从0到255。< / p >
2022-08-04 06:59:33 +00:00
< p > 下面是Go语言中关于算术运算、逻辑运算和比较运算的二元运算符, 它们按照优先级递减的顺序排列: < / p >
< pre > < code > * / % < < > > & & ^
+ - | ^
== != < < = > > =
& &
||
< / code > < / pre >
< p > 二元运算符有五种优先级。在同一个优先级,使用左优先结合规则,但是使用括号可以明确优先顺序,使用括号也可以用于提升优先级,例如< code > mask & (1 < < 28)< / code > 。< / p >
< p > 对于上表中前两行的运算符,例如+运算符还有一个与赋值相结合的对应运算符+=,可以用于简化赋值语句。< / p >
< p > 算术运算符< code > +< / code > 、< code > -< / code > 、< code > *< / code > 和< code > /< / code > 可以适用于整数、浮点数和复数,但是取模运算符%仅用于整数间的运算。对于不同编程语言,%取模运算的行为可能并不相同。在Go语言中, %取模运算符的符号和被取模数的符号总是一致的,因此< code > -5%3< / code > 和< code > -5%-3< / code > 结果都是-2。除法运算符< code > /< / code > 的行为则依赖于操作数是否全为整数,比如< code > 5.0/4.0< / code > 的结果是1.25, 但是5/4的结果是1, 因为整数除法会向着0方向截断余数。< / p >
< p > 一个算术运算的结果, 不管是有符号或者是无符号的, 如果需要更多的bit位才能正确表示的话, 就说明计算结果是溢出了。超出的高位的bit位部分将被丢弃。如果原始的数值是有符号类型, 而且最左边的bit位是1的话, 那么最终结果可能是负的, 例如int8的例子: < / p >
< pre > < code class = "language-Go" > var u uint8 = 255
fmt.Println(u, u+1, u*u) // " 255 0 1"
var i int8 = 127
fmt.Println(i, i+1, i*i) // " 127 -128 1"
< / code > < / pre >
< p > 两个相同的整数类型可以使用下面的二元比较运算符进行比较;比较表达式的结果是布尔类型。< / p >
< pre > < code > == 等于
!= 不等于
< 小于
< = 小于等于
> 大于
> = 大于等于
< / code > < / pre >
< p > 事实上,布尔型、数字类型和字符串等基本类型都是可比较的,也就是说两个相同类型的值可以用==和!=进行比较。此外,整数、浮点数和字符串可以根据比较结果排序。许多其它类型的值可能是不可比较的,因此也就可能是不可排序的。对于我们遇到的每种类型,我们需要保证规则的一致性。< / p >
< p > 这里是一元的加法和减法运算符:< / p >
< pre > < code > + 一元加法(无效果)
- 负数
< / code > < / pre >
< p > 对于整数,+x是0+x的简写, -x则是0-x的简写; 对于浮点数和复数, +x就是x, -x则是x 的负数。< / p >
< p > Go语言还提供了以下的bit位操作运算符, 前面4个操作运算符并不区分是有符号还是无符号数: < / p >
< pre > < code > & 位运算 AND
| 位运算 OR
^ 位运算 XOR
& ^ 位清空( AND NOT)
< < 左移
> > 右移
< / code > < / pre >
< p > 位操作运算符< code > ^< / code > 作为二元运算符时是按位异或( XOR) , 当用作一元运算符时表示按位取反; 也就是说, 它返回一个每个bit位都取反的数。位操作运算符< code > & ^< / code > 用于按位置零( AND NOT) : 如果对应y中bit位为1的话, 表达式< code > z = x & ^ y< / code > 结果z的对应的bit位为0, 否则z对应的bit位等于x相应的bit位的值。< / p >
< p > 下面的代码演示了如何使用位操作解释uint8类型值的8个独立的bit位。它使用了Printf函数的%b参数打印二进制格式的数字; 其中%08b中08表示打印至少8个字符宽度, 不足的前缀部分用0填充。< / p >
< pre > < code class = "language-Go" > var x uint8 = 1< < 1 | 1< < 5
var y uint8 = 1< < 1 | 1< < 2
fmt.Printf(" %08b\n" , x) // " 00100010" , the set {1, 5}
fmt.Printf(" %08b\n" , y) // " 00000110" , the set {1, 2}
fmt.Printf(" %08b\n" , x& y) // " 00000010" , the intersection {1}
fmt.Printf(" %08b\n" , x|y) // " 00100110" , the union {1, 2, 5}
fmt.Printf(" %08b\n" , x^y) // " 00100100" , the symmetric difference {2, 5}
fmt.Printf(" %08b\n" , x& ^y) // " 00100000" , the difference {5}
for i := uint(0); i < 8; i++ {
if x& (1< < i) != 0 { // membership test
fmt.Println(i) // " 1" , " 5"
}
}
fmt.Printf(" %08b\n" , x< < 1) // " 01000100" , the set {2, 6}
fmt.Printf(" %08b\n" , x> > 1) // " 00010001" , the set {0, 4}
< / code > < / pre >
< p > ( 6.5节给出了一个可以远大于一个字节的整数集的实现。)< / p >
< p > 在< code > x< < n< / code > 和< code > x> > n< / code > 移位运算中, 决定了移位操作的bit数部分必须是无符号数; 被操作的x可以是有符号数或无符号数。算术上, 一个< code > x< < n< / code > 左移运算等价于乘以$2^n$,一个< code > x> > n< / code > 右移运算等价于除以$2^n$。< / p >
< p > 左移运算用零填充右边空缺的bit位, 无符号数的右移运算也是用0填充左边空缺的bit位, 但是有符号数的右移运算会用符号位的值填充左边空缺的bit位。因为这个原因, 最好用无符号运算, 这样你可以将整数完全当作一个bit位模式处理。< / p >
< p > 尽管Go语言提供了无符号数的运算, 但即使数值本身不可能出现负数, 我们还是倾向于使用有符号的int类型, 就像数组的长度那样, 虽然使用uint无符号类型似乎是一个更合理的选择。事实上, 内置的len函数返回一个有符号的int, 我们可以像下面例子那样处理逆序循环。< / p >
< pre > < code class = "language-Go" > medals := []string{" gold" , " silver" , " bronze" }
for i := len(medals) - 1; i > = 0; i-- {
fmt.Println(medals[i]) // " bronze" , " silver" , " gold"
}
< / code > < / pre >
< p > 另一个选择对于上面的例子来说将是灾难性的。如果len函数返回一个无符号数, 那么i也将是无符号的uint类型, 然后条件< code > i > = 0< / code > 则永远为真。在三次迭代之后,也就是< code > i == 0< / code > 时, i--语句将不会产生-1, 而是变成一个uint类型的最大值( 可能是$2^64-1$) , 然后medals[i]表达式运行时将发生panic异常( §5.9) , 也就是试图访问一个slice范围以外的元素。< / p >
< p > 出于这个原因, 无符号数往往只有在位运算或其它特殊的运算场景才会使用, 就像bit集合、分析二进制文件格式或者是哈希和加密操作等。它们通常并不用于仅仅是表达非负数量的场合。< / p >
< p > 一般来说,需要一个显式的转换将一个值从一种类型转化为另一种类型,并且算术和逻辑运算的二元操作中必须是相同的类型。虽然这偶尔会导致需要很长的表达式,但是它消除了所有和类型相关的问题,而且也使得程序容易理解。< / p >
< p > 在很多场景,会遇到类似下面代码的常见的错误:< / p >
< pre > < code class = "language-Go" > var apples int32 = 1
var oranges int16 = 2
var compote int = apples + oranges // compile error
< / code > < / pre >
< p > 当尝试编译这三个语句时,将产生一个错误信息:< / p >
< pre > < code > invalid operation: apples + oranges (mismatched types int32 and int16)
< / code > < / pre >
< p > 这种类型不匹配的问题可以有几种不同的方法修复,最常见方法是将它们都显式转型为一个常见类型:< / p >
< pre > < code class = "language-Go" > var compote = int(apples) + int(oranges)
< / code > < / pre >
< p > 如2.5节所述, 对于每种类型T, 如果转换允许的话, 类型转换操作T(x)将x转换为T类型。许多整数之间的相互转换并不会改变数值; 它们只是告诉编译器如何解释这个值。但是对于将一个大尺寸的整数类型转为一个小尺寸的整数类型, 或者是将一个浮点数转为整数, 可能会改变数值或丢失精度: < / p >
< pre > < code class = "language-Go" > f := 3.141 // a float64
i := int(f)
fmt.Println(f, i) // " 3.141 3"
f = 1.99
fmt.Println(int(f)) // " 1"
< / code > < / pre >
< p > 浮点数到整数的转换将丢失任何小数部分,然后向数轴零方向截断。你应该避免对可能会超出目标类型表示范围的数值做类型转换,因为截断的行为可能依赖于具体的实现:< / p >
< pre > < code class = "language-Go" > f := 1e100 // a float64
i := int(f) // 结果依赖于具体实现
< / code > < / pre >
< p > 任何大小的整数字面值都可以用以0开始的八进制格式书写, 例如0666; 或用以0x或0X开头的十六进制格式书写, 例如0xdeadbeef。十六进制数字可以用大写或小写字母。如今八进制数据通常用于POSIX操作系统上的文件访问权限标志, 十六进制数字则更强调数字值的bit位模式。< / p >
< p > 当使用fmt包打印一个数值时, 我们可以用%d、%o或%x参数控制输出的进制格式, 就像下面的例子: < / p >
< pre > < code class = "language-Go" > o := 0666
fmt.Printf(" %d %[1]o %#[1]o\n" , o) // " 438 666 0666"
x := int64(0xdeadbeef)
fmt.Printf(" %d %[1]x %#[1]x %#[1]X\n" , x)
// Output:
// 3735928559 deadbeef 0xdeadbeef 0XDEADBEEF
< / code > < / pre >
< p > 请注意fmt的两个使用技巧。通常Printf格式化字符串包含多个%参数时将会包含对应相同数量的额外操作数,但是%之后的< code > [1]< / code > 副词告诉Printf函数再次使用第一个操作数。第二, %后的< code > #< / code > 副词告诉Printf在用%o、%x或%X输出时生成0、0x或0X前缀。< / p >
< p > 字符面值通过一对单引号直接包含对应字符。最简单的例子是ASCII中类似'a'写法的字符面值, 但是我们也可以通过转义的数值来表示任意的Unicode码点对应的字符, 马上将会看到这样的例子。< / p >
< p > 字符使用< code > %c< / code > 参数打印,或者是用< code > %q< / code > 参数打印带单引号的字符:< / p >
< pre > < code class = "language-Go" > ascii := 'a'
unicode := '国'
newline := '\n'
fmt.Printf(" %d %[1]c %[1]q\n" , ascii) // " 97 a 'a'"
fmt.Printf(" %d %[1]c %[1]q\n" , unicode) // " 22269 国 '国'"
fmt.Printf(" %d %[1]q\n" , newline) // " 10 '\n'"
< / code > < / pre >
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