英文:
Map of counetrs html tags in Golang dont work properly
问题
我遇到了一个问题。
我需要编写一个函数，将元素名称（如p、div、span等）映射到HTML文档树中具有该名称的元素数量。我编写了一个名为outline2的函数，但它不起作用，这是错误日志：
html
panic: assignment to entry in nil map
goroutine 1 [running]:
panic(0x4c3b40, 0xc042010a90)
F:/Go/src/runtime/panic.go:500 +0x1af
main.outline2(0x0, 0xc0420320e0)
F:/Go_Stuff/Books/Golang_stuff/exercises/src/gopl.io/ch5/outline/main.go:29 +0x1ae
main.outline2(0x0, 0xc042032070)
F:/Go_Stuff/Books/Golang_stuff/exercises/src/gopl.io/ch5/outline/main.go:34 +0xe3
main.main()
F:/Go_Stuff/Books/Golang_stuff/exercises/src/gopl.io/ch5/outline/main.go:23 +0x77
以下是代码：
func main() {
doc, err := html.Parse(os.Stdin)
if err != nil {
fmt.Fprintf(os.Stderr, "outline: %v\n", err)
os.Exit(1)
}
outline2(nil, doc)
}
func outline2(tags map[string]int, n *html.Node) {
fmt.Println(n.Data)
if n.Type == html.ElementNode {
fmt.Println(n.Data)
tags[n.Data] += 1 // push tag
fmt.Println(n.Data)
}
for c := n.FirstChild; c != nil; c = c.NextSibling {
outline2(tags, c)
}
}
请指出我的错误。我不知道该怎么办 =(
英文:
I got a problem.
I need to write a function to populate a mapping from element names—p, div, span, and so on — to the number of elements with that name in an HTML document tree. I made function outline2, it's not working, here is the eroor log:
html
panic: assignment to entry in nil map
goroutine 1 [running]:
panic(0x4c3b40, 0xc042010a90)
F:/Go/src/runtime/panic.go:500 +0x1af
main.outline2(0x0, 0xc0420320e0)
F:/Go_Stuff/Books/Golang_stuff/exercises/src/gopl.io/ch5/outline/main.go:29 +0x1ae
main.outline2(0x0, 0xc042032070)
F:/Go_Stuff/Books/Golang_stuff/exercises/src/gopl.io/ch5/outline/main.go:34 +0xe3
main.main()
F:/Go_Stuff/Books/Golang_stuff/exercises/src/gopl.io/ch5/outline/main.go:23 +0x77
Here is the code:
func main() {
doc, err := html.Parse(os.Stdin)
if err != nil {
fmt.Fprintf(os.Stderr, "outline: %v\n", err)
os.Exit(1)
}
outline2(nil, doc)
}
func outline2(tags map[string]int, n *html.Node) {
fmt.Println(n.Data)
if n.Type == html.ElementNode {
fmt.Println(n.Data)
tags[n.Data] += 1 // push tag
fmt.Println(n.Data)
}
for c := n.FirstChild; c != nil; c = c.NextSibling {
outline2(tags, c)
}
}
Please, point out my mistakes. I don't know what to do =(
答案1
得分: 1
错误是准确的。你不能在空映射中进行赋值。你必须先分配空间。另外，你的函数没有返回任何内容，所以应该这样做：
outline := make(map[string]int) //分配并命名你的映射
outline2(outline, doc)
fmt.Println(outline) //对其进行操作
应该可以工作。
英文:
Error is exact. You can't assign in nil map. You must first allocate. Also you need something to work, you func return nothing. So
outline := make(map[string]int) //allocate and name your map
outline2(outline, doc)
fmt.Println(outline) //do something with it
should work
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