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< 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.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" class = "active" > < 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" > < 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.< / strong > JSON< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-06.html" > < s
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< 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 >
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< h2 id = "11-hello-world" > < a class = "header" href = "#11-hello-world" > 1.1. Hello, World< / a > < / h2 >
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< p > 我们以现已成为传统的“hello world”案例来开始吧， < a href = "http://s3-us-west-2.amazonaws.com/belllabs-microsite-dritchie/cbook/index.html" > 《The C Programming Language》< / a > （译注：本书作者之一 Brian W. Kernighan 也是《The C Programming Language》一书的作者） < / p >
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< p > < u > < i > gopl.io/ch1/helloworld< / i > < / u > < / p >
< pre > < code class = "language-go" > package main
import " fmt"
func main() {
fmt.Println(" Hello, 世界" )
}
< / code > < / pre >
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< p > Go 是一门编译型语言， （ ： ） < code > go< / code > 调用，< code > go< / code > 命令有一系列子命令。最简单的一个子命令就是 < code > run< / code > 。这个命令编译一个或多个以。< code > .go< / code > 结尾的源文件，链接库文件，并运行最终生成的可执行文件。（本书使用$表示命令行提示符。）< / p >
< pre > < code class = "language-bash" > $ go run helloworld.go
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< / code > < / pre >
< p > 毫无意外，这个命令会输出：< / p >
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< pre > < code class = "language-text" > Hello, 世界
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< / code > < / pre >
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< p > Go 语言原生支持 Unicode， < / p >
< p > 如果不只是一次性实验，你肯定希望能够编译这个程序，保存编译结果以备将来之用。可以用 < code > build< / code > 子命令：< / p >
< pre > < code class = "language-shell" > $ go build helloworld.go
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< / code > < / pre >
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< p > 这个命令生成一个名为 < code > helloworld< / code > 的可执行的二进制文件（ ： < code > helloworld.exe< / code > ，增加了 < code > .exe< / code > 后缀名），之后你可以随时运行它（译注：在 Windows 系统下在命令行直接输入 < code > helloworld.exe< / code > 命令运行），不需任何处理（译注：因为静态编译，所以不用担心在系统库更新的时候冲突，幸福感满满）。< / p >
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< pre > < code > $ ./helloworld
Hello, 世界
< / code > < / pre >
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< p > 本书中所有示例代码上都有一行标记，利用这些标记可以从 < a href = "http://gopl.io" > gopl.io< / a > 网站上本书源码仓库里获取代码：< / p >
< pre > < code class = "language-text" > gopl.io/ch1/helloworld
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< / code > < / pre >
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< p > 执行 < code > go get gopl.io/ch1/helloworld< / code > 命令，就会从网上获取代码，并放到对应目录中（需要先安装 Git 或 Hg 之类的版本管理工具，并将对应的命令添加到 < code > PATH< / code > 环境变量中。序言已经提及，需要先设置好 < code > GOPATH< / code > 环境变量，下载的代码会放在 < code > $GOPATH/src/gopl.io/ch1/helloworld< / code > 目录）。< a href = "../ch2/ch2-06.html" > 2.6< / a > 和 < a href = "../ch10/ch10-07.html" > 10.7 节< / a > 有这方面更详细的介绍。< / p >
< p > 来讨论下程序本身。Go 语言的代码通过< strong > 包< / strong > （ ） ， （ ） （ ） < code > .go< / code > 源代码文件组成，目录定义包的作用。每个源文件都以一条 < code > package< / code > 声明语句开始，这个例子里就是 < code > package main< / code > ， ， （ ） ， < / p >
< p > Go 的标准库提供了 100 多个包，以支持常见功能，如输入、输出、排序以及文本处理。比如 < code > fmt< / code > 包，就含有格式化输出、接收输入的函数。< code > Println< / code > 是其中一个基础函数，可以打印以空格间隔的一个或多个值，并在最后添加一个换行符，从而输出一整行。< / p >
< p > < code > main< / code > 包比较特殊。它定义了一个独立可执行的程序，而不是一个库。在 < code > main< / code > 里的 < code > main< / code > < em > 函数< / em > 也很特殊， （ ： < code > main< / code > 函数所做的事情就是程序做的。当然了，< code > main< / code > 函数一般调用其它包里的函数完成很多工作（如：< code > fmt.Println< / code > ）。< / p >
< p > 必须告诉编译器源文件需要哪些包，这就是跟随在 < code > package< / code > 声明后面的 < code > import< / code > 声明扮演的角色。< code > hello world< / code > 例子只用到了一个包，大多数程序需要导入多个包。< / p >
< p > 必须恰当导入需要的包， ， （ ： < / p >
< p > < code > import< / code > 声明必须跟在文件的 < code > package< / code > 声明之后。随后，则是组成程序的函数、变量、常量、类型的声明语句（分别由关键字 < code > func< / code > 、< code > var< / code > 、< code > const< / code > 、< code > type< / code > 定义）。这些内容的声明顺序并不重要（译注：最好还是定一下规范）。这个例子的程序已经尽可能短了，只声明了一个函数，其中只调用了一个其他函数。为了节省篇幅，有些时候示例程序会省略 < code > package< / code > 和 < code > import< / code > 声明，但是，这些声明在源代码里有，并且必须得有才能编译。< / p >
< p > 一个函数的声明由 < code > func< / code > 关键字、函数名、参数列表、返回值列表（这个例子里的 < code > main< / code > 函数参数列表和返回值都是空的）以及包含在大括号里的函数体组成。第五章进一步考察函数。< / p >
< p > Go 语言不需要在语句或者声明的末尾添加分号，除非一行上有多条语句。实际上，编译器会主动把特定符号后的换行符转换为分号，因此换行符添加的位置会影响 Go 代码的正确解析（译注：比如行末是标识符、整数、浮点数、虚数、字符或字符串文字、关键字 < code > break< / code > 、< code > continue< / code > 、< code > fallthrough< / code > 或 < code > return< / code > 中的一个、运算符和分隔符 < code > ++< / code > 、< code > --< / code > 、< code > )< / code > 、< code > ]< / code > 或 < code > }< / code > 中的一个）。举个例子，函数的左括号 < code > {< / code > 必须和 < code > func< / code > 函数声明在同一行上，且位于末尾，不能独占一行，而在表达式 < code > x+y< / code > 中，可在 < code > +< / code > 后换行，不能在 < code > +< / code > 前换行（译注：以+结尾的话不会被插入分号分隔符，但是以 x 结尾的话则会被分号分隔符，从而导致编译错误）。< / p >
< p > Go 语言在代码格式上采取了很强硬的态度。< code > gofmt< / code > 工具把代码格式化为标准格式（ ： ， < code > go< / code > 工具中的 < code > fmt< / code > 子命令会对指定包， < code > gofmt< / code > 命令。本书中的所有代码都被 gofmt 过。你也应该养成格式化自己的代码的习惯。以法令方式规定标准的代码格式可以避免无尽的无意义的琐碎争执（译注：也导致了 Go 语言的 TIOBE 排名较低，因为缺少撕逼的话题）。更重要的是，这样可以做多种自动源码转换，如果放任 Go 语言代码格式，这些转换就不大可能了。< / p >
< p > 很多文本编辑器都可以配置为保存文件时自动执行 < code > gofmt< / code > ，这样你的源代码总会被恰当地格式化。还有个相关的工具：< code > goimports< / code > ，可以根据代码需要，自动地添加或删除 < code > import< / code > 声明。这个工具并没有包含在标准的分发包中，可以用下面的命令安装：< / p >
< pre > < code class = "language-shell" > $ go get golang.org/x/tools/cmd/goimports
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< / code > < / pre >
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< p > 对于大多数用户来说，下载、编译包、运行测试用例、察看 Go 语言的文档等等常用功能都可以用 go 的工具完成。< a href = "../ch10/ch10-07.html" > 10.7 节< / a > 详细介绍这些知识。< / p >
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