为什么Go中的fmt.Scanf不等待用户输入? [英] Why doesn't fmt.Scanf in Go wait for user input?
问题描述
我正在研究Caleb Doxsey的Go书,我对fmt.Scanf
有两个问题. http://www .golang-book.com/4
I am working through Caleb Doxsey's Go book and I have two questions about fmt.Scanf
http://www.golang-book.com/4
我想知道为什么在第二次Scanf之后程序没有停止并等待用户输入?以及如何测试用户是否输入了整数和/或没有留空?
I am wondering why the program does not stop after the second Scanf and wait for user input? And how do I test if the user entered an integer and/or did not leave blank?
package main
import (
"fmt"
//"math"
)
// compute square roots by using Newton's method
func main() {
var x float64 //number to take square root
var y float64 //this is the guess
var q float64 //this is the quotient
var a float64 //this is the average
// how do check if the user entered a number
fmt.Print("Enter a number to take its square root: ")
var inputSquare float64
fmt.Scanf("%f", &inputSquare)
// why doesn't program stop after
// the Print statement and wait
// for user input?
fmt.Print("Enter first guess ")
var inputGuess float64
fmt.Scanf("%f", &inputGuess)
//x = 2
x = inputSquare
y = inputGuess
for i := 0; i < 10; i++ { //set up the for loop for iterations
q = x/y //compute the quotient; x and y are given
a = (q + y) / x //compute the average
y = a //set the guess to the average
} //for the next loop
fmt.Println("y --> ", y)
//fmt.Println("Sqrt(2)", math.Sqrt(2))
}
推荐答案
它是问题5391 :fmt
:Scanf
在Windows的行尾拒绝\r\n
.
It's Issue 5391: fmt
: Scanf
rejects \r\n
at end of line on Windows.
作为一种解决方法,要检查输入是否有效,请写
As a workaround and to check for valid input, write,
var inputSquare float64
n, err := fmt.Scanf("%f\n", &inputSquare)
if err != nil || n != 1 {
// handle invalid input
fmt.Println(n, err)
}
和
var inputGuess float64
n, err = fmt.Scanf("%f\n", &inputGuess)
if err != nil || n != 1 {
// handle invalid input
fmt.Println(n, err)
}
解决方法是使用"%f\n"
格式字符串的换行符.
The workaround is the newline in the "%f\n"
format strings.
包装
fmt
func Scanf(format string, a ...interface{}) (n int, err error)
Scanf
扫描从标准输入读取的文本,并连续存储
将空格分隔的值转换为由参数确定的连续参数
格式.它返回成功扫描的项目数.
Scanf
scans text read from standard input, storing successive
space-separated values into successive arguments as determined by the
format. It returns the number of items successfully scanned.
这是一个完整的工作程序:
Here's a complete working program:
package main
import (
"fmt"
)
// compute square roots by using Newton's method
func main() {
var x float64 //number to take square root
var y float64 //this is the guess
var q float64 //this is the quotient
var a float64 //this is the average
fmt.Print("Enter a number to take its square root: ")
var inputSquare float64
n, err := fmt.Scanf("%f\n", &inputSquare)
if err != nil || n != 1 {
// handle invalid input
fmt.Println(n, err)
return
}
fmt.Print("Enter first guess ")
var inputGuess float64
n, err = fmt.Scanf("%f\n", &inputGuess)
if err != nil || n != 1 {
// handle invalid input
fmt.Println(n, err)
return
}
x = inputSquare
y = inputGuess
for i := 0; i < 10; i++ {
q = x / y // compute the quotient; x and y are given
a = (q + y) / x // compute the average
y = a // set the guess to the average
}
fmt.Printf("sqrt(%g) = %g\n", x, y)
}
输出:
Enter a number to take its square root: 2.0
Enter first guess 1.0
sqrt(2) = 1.414213562373095
我在Windows 7上使用了Go 1.1.1:
I used Go 1.1.1 on Windows 7:
C:\>go version
go version go1.1.1 windows/amd64
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