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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" > < 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" > < strong aria-hidd
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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 = "54-错误" > < a class = "header" href = "#54-错误" > 5.4. 错误< / a > < / h2 >
< p > 在Go中有一部分函数总是能成功的运行。比如strings.Contains和strconv.FormatBool函数， ， ， ， ， ， < / p >
< p > 还有一部分函数只要输入的参数满足一定条件， ， ， （ ） ， < / p >
< p > 对于大部分函数而言， ， ， ， ， ， < / p >
< p > 在Go的错误处理中， ， < / p >
< p > 对于那些将运行失败看作是预期结果的函数， ， ， ， ， ， ， ： < / p >
< pre > < code class = "language-Go" > value, ok := cache.Lookup(key)
if !ok {
// ...cache[key] does not exist…
}
< / code > < / pre >
< p > 通常， ， ， ， ， < / p >
< p > 内置的error是接口类型。我们将在第七章了解接口类型的含义， ， ， < / p >
< pre > < code class = "language-Go" > fmt.Println(err)
fmt.Printf(" %v" , err)
< / code > < / pre >
< p > 通常， ， （ ） ， ， ， ， ， ， ， ， < / p >
< p > 在Go中， ， （ ） ， ， ， ， < / p >
< p > Go这样设计的原因是由于对于某个应该在控制流程中处理的错误而言， ， ， ， ， < / p >
< p > 正因此， （ ） ， < / p >
< h3 id = "541-错误处理策略" > < a class = "header" href = "#541-错误处理策略" > 5.4.1. 错误处理策略< / a > < / h3 >
< p > 当一次函数调用返回错误时，调用者应该选择合适的方式处理错误。根据情况的不同，有很多处理方式，让我们来看看常用的五种方式。< / p >
< p > 首先， ， ， ， ： < / p >
< pre > < code class = "language-Go" > resp, err := http.Get(url)
if err != nil{
return nil, err
}
< / code > < / pre >
< p > 当对html.Parse的调用失败时， ， ： （ ） ； ， ， ， < / p >
< pre > < code class = "language-Go" > doc, err := html.Parse(resp.Body)
resp.Body.Close()
if err != nil {
return nil, fmt.Errorf(" parsing %s as HTML: %v" , url,err)
}
< / code > < / pre >
< p > fmt.Errorf函数使用fmt.Sprintf格式化错误信息并返回。我们使用该函数添加额外的前缀上下文信息到原始错误信息。当错误最终由main函数处理时， ， ： < / p >
< pre > < code > genesis: crashed: no parachute: G-switch failed: bad relay orientation
< / code > < / pre >
< p > 由于错误信息经常是以链式组合在一起的， ， （ ： ） < / p >
< p > 编写错误信息时，我们要确保错误信息对问题细节的描述是详尽的。尤其是要注意错误信息表达的一致性，即相同的函数或同包内的同一组函数返回的错误在构成和处理方式上是相似的。< / p >
< p > 以os包为例， （ ） （ ， ） ， < / p >
< p > 一般而言， ， ， < / p >
< p > 让我们来看看处理错误的第二种策略。如果错误的发生是偶然性的，或由不可预知的问题导致的。一个明智的选择是重新尝试失败的操作。在重试时，我们需要限制重试的时间间隔或重试的次数，防止无限制的重试。< / p >
< p > < u > < i > gopl.io/ch5/wait< / i > < / u > < / p >
< pre > < code class = "language-Go" > // WaitForServer attempts to contact the server of a URL.
// It tries for one minute using exponential back-off.
// It reports an error if all attempts fail.
func WaitForServer(url string) error {
const timeout = 1 * time.Minute
deadline := time.Now().Add(timeout)
for tries := 0; time.Now().Before(deadline); tries++ {
_, err := http.Head(url)
if err == nil {
return nil // success
}
log.Printf(" server not responding (%s);retrying…" , err)
time.Sleep(time.Second < < uint(tries)) // exponential back-off
}
return fmt.Errorf(" server %s failed to respond after %s" , url, timeout)
}
< / code > < / pre >
< p > 如果错误发生后， ， ： ， ， ， ， ， < / p >
< pre > < code class = "language-Go" > // (In function main.)
if err := WaitForServer(url); err != nil {
fmt.Fprintf(os.Stderr, " Site is down: %v\n" , err)
os.Exit(1)
}
< / code > < / pre >
< p > 调用log.Fatalf可以更简洁的代码达到与上文相同的效果。log中的所有函数， < / p >
< pre > < code class = "language-Go" > if err := WaitForServer(url); err != nil {
log.Fatalf(" Site is down: %v\n" , err)
}
< / code > < / pre >
< p > 长时间运行的服务器常采用默认的时间格式，而交互式工具很少采用包含如此多信息的格式。< / p >
< pre > < code > 2006/01/02 15:04:05 Site is down: no such domain:
bad.gopl.io
< / code > < / pre >
< p > 我们可以设置log的前缀信息屏蔽时间信息， ， < / p >
< pre > < code class = "language-Go" > log.SetPrefix(" wait: " )
log.SetFlags(0)
< / code > < / pre >
< p > 第四种策略： ， ， < / p >
< pre > < code class = "language-Go" > if err := Ping(); err != nil {
log.Printf(" ping failed: %v; networking disabled" ,err)
}
< / code > < / pre >
< p > 或者标准错误流输出错误信息。< / p >
< pre > < code class = "language-Go" > if err := Ping(); err != nil {
fmt.Fprintf(os.Stderr, " ping failed: %v; networking disabled\n" , err)
}
< / code > < / pre >
< p > log包中的所有函数会为没有换行符的字符串增加换行符。< / p >
< p > 第五种，也是最后一种策略：我们可以直接忽略掉错误。< / p >
< pre > < code class = "language-Go" > dir, err := ioutil.TempDir(" " , " scratch" )
if err != nil {
return fmt.Errorf(" failed to create temp dir: %v" ,err)
}
// ...use temp dir…
os.RemoveAll(dir) // ignore errors; $TMPDIR is cleaned periodically
< / code > < / pre >
< p > 尽管os.RemoveAll会失败， ， ， ， ， ， < / p >
< p > 在Go中， ， ， ， ， ， ， < / p >
< h3 id = "542-文件结尾错误eof" > < a class = "header" href = "#542-文件结尾错误eof" > 5.4.2. 文件结尾错误（ ） < / a > < / h3 >
< p > 函数经常会返回多种错误， ， ， ， ， ： ， ， ， ， ： < / p >
< pre > < code class = "language-Go" > package io
import " errors"
// EOF is the error returned by Read when no more input is available.
var EOF = errors.New(" EOF" )
< / code > < / pre >
< p > 调用者只需通过简单的比较， ， （ ） < / p >
< pre > < code class = "language-Go" > in := bufio.NewReader(os.Stdin)
for {
r, _, err := in.ReadRune()
if err == io.EOF {
break // finished reading
}
if err != nil {
return fmt.Errorf(" read failed:%v" , err)
}
// ...use r…
}
< / code > < / pre >
< p > 因为文件结束这种错误不需要更多的描述， ， ， < / p >
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