英文:
pushback to vector in Golang causes program crash
问题
func extract_word(r rune) bool {
return !unicode.IsLetter(r)
}
type kv_string_value struct {
str string
num int
}
func Map(value string) *list.List {
t := strings.FieldsFunc(value, extract_word)
fmt.Println("t:", len(t))
m := make(map[string]int)
for _, word := range t {
m[word]++
}
var x *list.List
for k, v := range m {
pair := kv_string_value{}
pair.str = k
pair.num = v
x.PushBack(pair)
fmt.Println("Good5")
}
return x
}
这段代码中的问题在于 x 是一个指向 list.List 的指针，但是它没有被初始化。因此，在调用 x.PushBack(pair) 时会导致空指针解引用错误。你需要在使用 x 之前先对其进行初始化，可以使用 x := list.New() 来创建一个新的 list.List 对象。这样就可以正常地将 pair 添加到列表中了。
英文:
func extract_word(r rune) bool {
return !unicode.IsLetter(r)
}
type kv_string_value struct {
str string
num int
}
func Map(value string) *list.List {
t := strings.FieldsFunc(value, extract_word)
fmt.Println("t:", len(t))
m := make(map[string]int)
for _, word := range t{
m[word]++
}
var x *list.List
for k,v := range m {
pair := kv_string_value{}
pair.str = k
pair.num = v
x.PushBack(pair)
fmt.Println("Good5")
}
return x
}
Something wrong with this "x.PushBack(pair)"
it just pushback a pair to a list, why it crash my program?
need help.
thanks!
/main$ go run wc.go master kjv12.txt sequential
# command-line-arguments
./wc.go:34: *x.PushBack(pair) evaluated but not used
main$ go run wc.go master kjv12.txt sequential
Split kjv12.txt
name is mrtmp.kjv12.txt-0
DoMap: read split mrtmp.kjv12.txt-0 966967
Read succesful.
t: 160040
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x0 pc=0x444c25]
goroutine 1 [running]:
runtime.panic(0x6874a0, 0x9c5a48)
/usr/lib/go/src/pkg/runtime/panic.c:266 +0xb6
container/list.(*List).lazyInit(0x0)
/usr/lib/go/src/pkg/container/list/list.go:86 +0x5
container/list.(*List).PushBack(0x0, 0x68ce20, 0xc210084240, 0x2)
/usr/lib/go/src/pkg/container/list/list.go:138 +0x27
答案1
得分: 6
错误出在：
var x *list.List
你声明了一个指向 list.List 的指针，但没有创建实例。x 的初始值将为 nil。要使你的代码正常工作，将该行改为：
x := list.New()
英文:
The bug lies in:
var x *list.List
You declare a pointer to a list.List without creating an instance of it. x will have the initial value of nil. To make your code work, change the line to:
x := list.New()
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