使用http.Get()时无效的内存地址或无指针取消引用 [英] invalid memory address or nil pointer dereference when use http.Get()
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问题描述
我刚开始学习Go lang,我写了一个小demo,从txt读取图片url,将urls放入数组,然后将Save Response保存到文件中。
这是我的代码
包主
导入(
bufio
fmt
io
io / ioutil
净/ http
os
)
func main(){
fileName:=meinv.txt
file,_:= os.Open(fileName)
$ b $ picUrl:= make([] string, 2000)
reader:= bufio.NewReader(文件)
为{
line,_,err:= reader.ReadLine()
if err!= io.EOF {
fmt.Printf(file load%s \\\
,line)
picUrl = append(picUrl,string(line))
} else {
file.Close()
break
$ b fmt.Printf(file loaded,read to download \\\
)
fetchPic(picUrl)
}
func fetchPic(picUrl [] string){
var file string
for key,value:= range picUrl {
fmt.Printf (关键是:%d,这一行是%s \\\
\\\
,key,value)
httpRequest,err:= http.Get(string(value))
fmt.Print(load ok \\\
)
httpRequest.Body.Close()
result,readErr:= ioutil.ReadAll(httpRequest.Body)
if readErr == nil {
file =pics /+ string (key)+.jpg
ioutil.WriteFile(file,result,0777)
fmt.Print(Write ok \\\
)
}
len:= len(字符串(结果))
fmt.Printf(长度为%d,len)
如果err == nil {
httpRequest = nil
// result = nil
} else {
fmt.Print(load falt !!!!!!!!! \\\
)
}
推迟httpRequest.Body.Close()
}
}
运行它,我得到了
键是:0,这行是
加载ok
panic:运行时错误:无效内存地址或零指针解引用
[信号0xb代码= 0x1地址= 0x40 pc = 0x40123f]
goroutine 1 [running]:
runtime.panic(0x5f8300,0x877688)
/usr/local/go/src/pkg/runtime/panic.c:266 + 0xb6
main.fetchPic(0xc21239d000,0x38be7,0x4223c)
/home/lyn/www/goOnDev/fetch.go:40+ 0x24f
main.main()
/ home / lyn / www / goOnDev / fetch.go:28 + 0x1b8
退出状态2
meinv.txt,one每个网址的行
任何帮助?THKS
解决方案您正在阅读无条件的httpRequest.Body后做
httpRequest,err:= http.Get(string(value))
不检查err:如果 http.Get
失败,您将不会拥有一个有效的 httpRequest.Body
阅读。 经验法则:立即检查每个错误。
I just start to learn Go lang,I wrote a small demo,read picture urls from txt,put urls in an array,then Save the Response into a file.
Here is my code
package main
import (
"bufio"
"fmt"
"io"
"io/ioutil"
"net/http"
"os"
)
func main() {
fileName := "meinv.txt"
file, _ := os.Open(fileName)
picUrl := make([]string, 2000)
reader := bufio.NewReader(file)
for {
line, _, err := reader.ReadLine()
if err != io.EOF {
fmt.Printf("file load %s \n", line)
picUrl = append(picUrl, string(line))
} else {
file.Close()
break
}
}
fmt.Printf("file loaded,read to download \n")
fetchPic(picUrl)
}
func fetchPic(picUrl []string) {
var file string
for key, value := range picUrl {
fmt.Printf("key is : %d,this line is %s \n\n", key, value)
httpRequest, err := http.Get(string(value))
fmt.Print("load ok \n")
httpRequest.Body.Close()
result, readErr := ioutil.ReadAll(httpRequest.Body)
if readErr == nil {
file = "pics/" + string(key) + ".jpg"
ioutil.WriteFile(file, result, 0777)
fmt.Print("Write ok \n")
}
len := len(string(result))
fmt.Printf("length is %d", len)
if err == nil {
httpRequest = nil
//result = nil
} else {
fmt.Print("load falt!!!!!!!!! \n")
}
defer httpRequest.Body.Close()
}
}
run it ,and I got
key is : 0,this line is
load ok
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x40 pc=0x40123f]
goroutine 1 [running]:
runtime.panic(0x5f8300, 0x877688)
/usr/local/go/src/pkg/runtime/panic.c:266 +0xb6
main.fetchPic(0xc21239d000, 0x38be7, 0x4223c)
/home/lyn/www/goOnDev/fetch.go:40 +0x24f
main.main()
/home/lyn/www/goOnDev/fetch.go:28 +0x1b8
exit status 2
meinv.txt ,one line per url Anyone help?THKS
解决方案
You are reading unconditional from httpRequest.Body after doing httpRequest, err := http.Get(string(value))
without checking err: If http.Get
fails you won't have a valid httpRequest.Body
to read from.
Rule of thumb: Check each and every error immediately.
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