Number Parsing

Parsing numbers from strings is a basic but common task in many programs; here's how to do it in Go.

package main

The built-in package strconv provides the number parsing.

import (
	"fmt"
	"strconv"
)

func main() {

With ParseFloat, this 64 tells how many bits of precision to parse.

	f, _ := strconv.ParseFloat("1.234", 64)
	fmt.Println(f)

For ParseInt, the 0 means infer the base from the string. 64 requires that the result fit in 64 bits.

	i, _ := strconv.ParseInt("123", 0, 64)
	fmt.Println(i)

ParseInt will recognize hex-formatted numbers.

	d, _ := strconv.ParseInt("0x1c8", 0, 64)
	fmt.Println(d)

A ParseUint is also available.

	u, _ := strconv.ParseUint("789", 0, 64)
	fmt.Println(u)

Atoi is a convenience function for basic base-10 int parsing.

	k, _ := strconv.Atoi("135")
	fmt.Println(k)

Parse functions return an error on bad input.

	_, e := strconv.Atoi("wat")
	fmt.Println(e)

Values that do not fit are reported too.

	_, e = strconv.ParseInt("300", 10, 8)
	fmt.Println(e)

ParseBool accepts 1, t, T, TRUE, true, True, and their false counterparts.

	b, _ := strconv.ParseBool("true")
	fmt.Println(b)

Going the other way: Itoa, FormatInt with a base, FormatFloat, and Quote.

	fmt.Println(strconv.Itoa(42), strconv.FormatInt(255, 2), strconv.FormatFloat(3.14159, 'f', 2, 64))
	fmt.Println(strconv.Quote("tab\there"))
}

$ go run ./68_number_parsing
1.234
123
456
789
135
strconv.Atoi: parsing "wat": invalid syntax
strconv.ParseInt: parsing "300": value out of range
true
42 11111111 3.14
"tab\there"

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