运行时错误:“分配给nil映射中的条目” [英] Runtime error: "assignment to entry in nil map"
问题描述
我正在尝试创建一部分地图。虽然代码编译得很好,但我得到了下面的运行时错误:
mapassign1:runtime·panicstring(赋值给nil映射);
我尝试制作一个Maps数组,每个Map包含两个标记,一个Id和一个投资者。我的代码如下所示:
for _,row:= range rows {
var inv_ids [] string
var inv_names [] string
//从MySQL创建数据数组GROUP_CONCAT函数
inv_ids = strings.Split(row.Str(10),,)
inv_names = strings.Split(row.Str(11),,)
length:= len(inv_ids);
invs:= make([] map [string] string,length)
//建立ids =为i:= 0命名
;我<长度; i ++ {
invs [i] = make(map [string] string)
invs [i] [Id] = inv_ids [i]
invs [i] [Investor] = inv_names [i]
} //对于
//构建消息并返回
msg:= InfoMessage {row.Int(0),row.Int(1), row.Str(2),row.Int(3),row.Str(4),row.Float(5),row.Float(6),row.Str(7),row.Str(8),row .Int(9),invs}
return(msg)
} // for
我最初认为像下面这样的东西会起作用,但是这并没有解决问题。任何想法?
$ p $ invs:= make([] make(map [string] string),length)
您正尝试创建切片 ;考虑下面的例子:
http://play.golang.org / p / gChfTgtmN-
包主
$ b $导入fmt
func main(){
a:= make([] map [string] int,100)
for i:= 0;我< 100; i ++ {
a [i] = map [string] int {id:i,投资者:i}
}
fmt.Println(a)
}
您可以重写这些行:
invs [i] = make(map [string] string)
invs [i] [Id] = inv_ids [i]
invs [ ] = inv_names [i]
as:
invs [i] = map [string] string {Id:inv_ids [i],Investor:inv_names [i]}
这就是所谓的复合文字。
在一个更习惯的程序中,你很可能想用 struct
来表示投资者:
< a href =http://play.golang.org/p/vppK6y-c8g> http://play.golang.org/p/vppK6y-c8g
包主要
导入(
fmt
strconv
)
类型投资者结构{
Id int
名称字符串
}
func main(){
a:= make([] Investor,100 )
for i:= 0;我< 100; i ++ {
a [i] = Investor {Id:i,Name:John+ strconv.Itoa(i)}
fmt.Printf(%#v \ n,a [i] )
}
}
I'm trying to create a slice of Maps. Although the code compiles fine, I get the runtime error below:
mapassign1: runtime·panicstring("assignment to entry in nil map");
I attempt to make an array of Maps, with each Map containing two indicies, a "Id" and a "Investor". My code looks like this:
for _, row := range rows {
var inv_ids []string
var inv_names []string
//create arrays of data from MySQLs GROUP_CONCAT function
inv_ids = strings.Split(row.Str(10), ",")
inv_names = strings.Split(row.Str(11), ",")
length := len(inv_ids);
invs := make([]map[string]string, length)
//build map of ids => names
for i := 0; i < length; i++ {
invs[i] = make(map[string]string)
invs[i]["Id"] = inv_ids[i]
invs[i]["Investor"] = inv_names[i]
}//for
//build Message and return
msg := InfoMessage{row.Int(0), row.Int(1), row.Str(2), row.Int(3), row.Str(4), row.Float(5), row.Float(6), row.Str(7), row.Str(8), row.Int(9), invs}
return(msg)
} //for
I initially thought something like below would work, however that did not fix the issue either. Any ideas?
invs := make([]make(map[string]string), length)
You are trying to create a slice of maps; consider the following example:
http://play.golang.org/p/gChfTgtmN-
package main
import "fmt"
func main() {
a := make([]map[string]int, 100)
for i := 0; i < 100; i++ {
a[i] = map[string]int{"id": i, "investor": i}
}
fmt.Println(a)
}
You can rewrite these lines:
invs[i] = make(map[string]string)
invs[i]["Id"] = inv_ids[i]
invs[i]["Investor"] = inv_names[i]
as:
invs[i] = map[string]string{"Id": inv_ids[i], "Investor": inv_names[i]}
this is called a composite literal.
Now, in a more idiomatic program, you'd most probably want to use a struct
to represent an investor:
http://play.golang.org/p/vppK6y-c8g
package main
import (
"fmt"
"strconv"
)
type Investor struct {
Id int
Name string
}
func main() {
a := make([]Investor, 100)
for i := 0; i < 100; i++ {
a[i] = Investor{Id: i, Name: "John" + strconv.Itoa(i)}
fmt.Printf("%#v\n", a[i])
}
}
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