dqrmkdu25623 2018-03-27 15:53
浏览 69
已采纳

是否可以将“ fmt.Fscan”或“ fmt.Scan”用于标准I / O?

About the standard I\O in Golang, all tutorial on the net, Without exception, discuss and use bufio which I tested and worked fine.

But my question is about using fmt package for reading standard input which either gives me errors or trapped in a loop. According to the fmt.Scan documentation:

Scan scans text read from standard input, storing successive space-separated values into successive arguments. Newlines count as space. It returns the number of items successfully scanned. If that is less than the number of arguments, err will report why.

In the first sentence it is said that Scan reads from standard input, but it doesn't work at all! also for fmt.Fscan which have this signature:

func Fscan(r io.Reader, a ...interface{}) (n int, err error)

when I enter a word, it throws exceptions and I can't even understand them!

So, is it possible to use these 2 methods to read standard input?


for more information this is my code:

package main

import (
    "fmt"
    "os"
)

func main() {

    fmt.Print("pls enter name: ")

    var st *string

    n, err := fmt.Fscan(os.Stdin, st)

    fmt.Println(st)

    fmt.Println(n)
    fmt.Println(err)

}

EDIT: the error I get when entering a word in above code:

panic: runtime error: invalid memory address or nil pointer dereference [recover
ed]
        panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xc0000005 code=0x1 addr=0x8 pc=0x4977aa]

goroutine 1 [running]:
fmt.errorHandler(0xc04206be40)
        C:/development/Programming Languages/GO/src/fmt/scan.go:1031 +0x14f
panic(0x4b15a0, 0x544720)
        C:/development/Programming Languages/GO/src/runtime/panic.go:505 +0x237
fmt.(*ss).scanOne(0xc042044060, 0x76, 0x4a6460, 0x0)
        C:/development/Programming Languages/GO/src/fmt/scan.go:979 +0xc7a
fmt.(*ss).doScan(0xc042044060, 0xc04206bf48, 0x1, 0x1, 0x0, 0x0, 0x0)
        C:/development/Programming Languages/GO/src/fmt/scan.go:1040 +0x9d
fmt.Fscan(0x4de080, 0xc042004010, 0xc04206bf48, 0x1, 0x1, 0x0, 0x10, 0x4b36c0)
        C:/development/Programming Languages/GO/src/fmt/scan.go:123 +0xd2
main.main()
        C:/Users/Hamed/Documents/Go Projects/src/golang/learning/helloworld/firs
tApp.go:22 +0xe3
  • 写回答

2条回答 默认 最新

  • duanming0494 2018-03-27 16:06
    关注

    The first thing I notice with your code is that you're passing a nil pointer to fmt.Fscan, i.e. you declare the variable st as *string but the address does not yet exist. It should be written:

    var st string
    _, err := fmt.Fscan(os.Stdin, &st)
    if err != nil {
        fmt.Println(err)
    } 
    

    In my revised example, st now has a memory address (a string's zero value is ""), so it's address can be obtained using & and then passed to fmt.Fscan. Second, you should note how I handle err returned from fmt.Fscan - you simply print err, but what if an error is not returned? Then err is nil and your fmt.Println(err) is executed for no reason - it is idiomatic to handle returned errors conditionally, as is done in the above example.

    However it is more common to use fmt.Scanf like so:

    var st string
    fmt.Scanf("%s", &st)
    

    Read the docs for more information. The "fmt" package.

    本回答被题主选为最佳回答 , 对您是否有帮助呢?
    评论
查看更多回答(1条)

报告相同问题?

悬赏问题

  • ¥15 寻一个支付宝扫码远程授权登录的软件助手app
  • ¥15 解riccati方程组
  • ¥15 display:none;样式在嵌套结构中的已设置了display样式的元素上不起作用?
  • ¥30 用arduino开发esp32控制ps2手柄一直报错
  • ¥15 使用rabbitMQ 消息队列作为url源进行多线程爬取时,总有几个url没有处理的问题。
  • ¥15 Ubuntu在安装序列比对软件STAR时出现报错如何解决
  • ¥50 树莓派安卓APK系统签名
  • ¥65 汇编语言除法溢出问题
  • ¥15 Visual Studio问题
  • ¥20 求一个html代码,有偿