Reading an integer from standard input
How do I use the fmt.Scanf
function in Go to get an integer input from the stan开发者_JAVA百科dard input?
If this can't be done using fmt.Scanf
, what's the best way to read a single integer?
http://golang.org/pkg/fmt/#Scanf
All the included libraries in Go are well documented.
That being said, I believe
func main() {
var i int
_, err := fmt.Scanf("%d", &i)
}
does the trick
An alternative that can be a bit more concise is to just use fmt.Scan
:
package main
import "fmt"
func main() {
var i int
fmt.Scan(&i)
fmt.Println("read number", i, "from stdin")
}
This uses reflection on the type of the argument to discover how the input should be parsed.
http://golang.org/pkg/fmt/#Scan
Golang fmt.Scan is simpler than Golang fmt.Scanf (which is simpler than Clang scanf)
If fmt.Scan errors i.e. if not nil, log & return
1 Read single variable:
import (
"fmt"
"log"
)
var i int
if _, err := fmt.Scan(&i); err != nil {
log.Print(" Scan for i failed, due to ", err)
return
}
fmt.Println(i)
2 Read multiple variables:
import (
"fmt"
"log"
)
var i, j, k int
if _, err := fmt.Scan(&i, &j, &k); err != nil {
log.Print(" Scan for i, j & k failed, due to ", err)
return
}
fmt.Println(i, j, k)
Best of luck
Example from: http://www.sortedinf.com/?q=golang-in-1-hour
Here is my "Fast IO" method for reading positive integers. It could be improved with bitshifts and laying out memory in advance.
package main
import (
"io/ioutil"
"bufio"
"os"
"strconv"
)
func main() {
out := bufio.NewWriter(os.Stdout)
ints := getInts()
var T int64
T, ints = ints[0], ints[1:]
..
out.WriteString(strconv.Itoa(my_num) + "\n")
out.Flush()
}
}
func getInts() []int64 {
//assumes POSITIVE INTEGERS. Check v for '-' if you have negative.
var buf []byte
buf, _ = ioutil.ReadAll(os.Stdin)
var ints []int64
num := int64(0)
found := false
for _, v := range buf {
if '0' <= v && v <= '9' {
num = 10*num + int64(v - '0') //could use bitshifting here.
found = true
} else if found {
ints = append(ints, num)
found = false
num = 0
}
}
if found {
ints = append(ints, num)
found = false
num = 0
}
return ints
}
You can use fmt.Scanf
with a format specifier. The format specifier for the integer is %d. So you can use standard input like below.
func main() {
var someVar int
fmt.Scanf("%d", &someVar)
}
or else you can use fmt.Scan
or fmt.Scanln
as below.
func main() {
var someVar int
fmt.Scanln(&someVar)
}
You could also use bufio.NewReader
to read an integer from the standard input.
The below program:
Prompts for an integer input
Creates a bufio.Reader to read from standard input
Reads input till it encounters a newline character
'\n'
(Note that this will only read a single integer. Space separated values will not work)Removes the newline character
Converts string to int
package main
import (
"fmt"
"bufio"
"os"
"strconv"
"strings"
)
func getInt() error {
fmt.Println("Enter an integer")
userInput := bufio.NewReader(os.Stdin)
userVal, err := userInput.ReadString('\n')
if err != nil {
return err
}
input := strings.TrimSpace(userVal)
intVal, err := strconv.Atoi(input)
if err != nil {
return err
}
fmt.Printf("You entered: %d\n", intVal)
return nil
}
func main() {
getInt()
}
Why can't we just use a scanf? just like we use in C? it's working though.
package main
import "fmt"
func main() {
var i int
fmt.Scanf("%d", &i)
fmt.Println(i)
}
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