How to Convert string to integer type in Go

Created Mar 31, 2022 at 21:55

Modified Mar 31, 2022 at 22:39

strconv.Atoi Function

Package strconv implements conversions to and from string representations of basic data types.

package main

import (
  "fmt"
  "strconv"
)

func main() {

  i, err := strconv.Atoi("10") // i = 10
  if err != nil {
    //handle error
  }
  fmt.Printf("%T, %v\n", i, i)

  //If the input string isn’t in the integer format, then the function returns zero.
  i, err = strconv.Atoi("abc10") // i = 0
  if err != nil {
    //handle error
    fmt.Println(err)
  }
  fmt.Printf("%T, %v\n", i, i)

  i, err = strconv.Atoi("9223372036854775809") // i = 9223372036854775807
  if err != nil {
    //handle error
    fmt.Println(err)
  }
  fmt.Printf("%T, %v\n", i, i)

}

int, 10

strconv.Atoi: parsing "abc10": invalid syntax
int, 0

strconv.Atoi: parsing "9223372036854775809": value out of range
int, 9223372036854775807

Atoi is equivalent to ParseInt(s, 10, 0), converted to type int.

strconv.ParseInt Function

ParseInt interprets a string s in the given base (0, 2 to 36) and bit size (0 to 64) and returns the corresponding value i.

package main

import (
  "fmt"
  "strconv"
)

func main() {

  // func strconv.ParseInt(s string, base int, bitSize int) (i int64, err error)
  // fastest

  v64 := "-10"
  if s, err := strconv.ParseInt(v64, 10, 64); err == nil {
    fmt.Printf("%T, %v\n", s, s)
  }

  // contains invalid digits
  v64 = "abc1"
  if s, err := strconv.ParseInt(v64, 10, 64); err != nil {
    fmt.Println(err)
    fmt.Printf("%T, %v\n", s, s)
  }

  // func ParseUint(s string, base int, bitSize int) (uint64, error)
  // ParseUint is like ParseInt but for unsigned numbers.
  v64 = "100"
  if s, err := strconv.ParseUint(v64, 10, 64); err == nil {
    fmt.Printf("%T, %v\n", s, s)
  }
}

int64, -10

strconv.ParseInt: parsing "abc1": invalid syntax
int64, 0

uint64, 100

fmt.Sscanf Function

Sscanf scans the argument string, storing successive space-separated values into successive arguments as determined by the format. It returns the number of items successfully parsed. Newlines in the input must match newlines in the format.

package main

import "fmt"

func main() {
  
  var name string
  var car int
  var dead int

  // not terribly fast but most flexible
  n, err := fmt.Sscanf("80-Car Pileup on Pennsylvania Highway Leaves 6 Dead", "%d-Car Pileup on %s Highway Leaves %d Dead", &car, &name, &dead)
  if err != nil {
    panic(err)
  }
  fmt.Printf("%d: %s, %d, %d\n", n, name, car, dead)
}