`ParseInt`

A string in Go can contain digit characters like "123." We can convert this string to a number (an int) with the strconv.ParseInt method.

Other options

With Atoi we have a simpler way to call ParseInt. These methods return 2 values: the parsed integer itself, and an error code.

Example, `ParseInt`

Let us begin with this simple example. We import the strconv package at the top. We assign 2 values to the result of strconv.ParseInt.

Argument 1 We call ParseInt with 3 arguments—the first is the string we want to get an integer from.

Argument 2 This is the base of the string being parsed. Most numbers we use are base 10.

Argument 3 This is the bit size of the resulting int. 0 means int, while 6 (for example) means int16, with 16 bits.

package main

import (
    "fmt"
    "strconv"
)

func main() {
    value := "123"
    // Convert string to int.
    number, _ := strconv.ParseInt(value, 10, 0)
    // We now have an int.
    fmt.Println(number)
    if number == 123 {
        fmt.Println(true)
    }
}123
true

`Atoi`

This function bears the same name as the one from the C standard library. In Go it invokes ParseInt with a base of 10 and a bit size of 0.

Tip The Atoi call here is simpler than ParseInt. This gives it an advantage in readability in programs.

package main

import (
    "fmt"
    "strconv"
)

func main() {
    value := "456"
    // Use Atoi to parse string.
    number, _ := strconv.Atoi(value)

    fmt.Println(number)
    fmt.Println(number + 1)
}456
457

`FormatInt`

With this method, we convert an int to a string. This is the opposite conversion as ParseInt. With FormatInt, we must pass an int64 value—we cast in this example.

package main

import (
    "fmt"
    "strconv"
)

func main() {
    value := 1055

    // Convert int to string with FormatInt.
    // ... First convert to int64.
    result := strconv.FormatInt(int64(value), 10)
    fmt.Println(result)
    if result == "1055" {
        fmt.Println(true)
    }
}1055
true

`Itoa`

This method converts an int into a string. It calls FormatInt with a base of 10. It also accepts a simple int, not an int64, so less casting may be required.

Note Unlike ParseInt and Atoi, FormatInt and Itoa do not return an error value. They succeed on all possible arguments.

package main

import (
    "fmt"
    "strconv"
)

func main() {
    value := 700

    // Use Itoa on an int.
    result := strconv.Itoa(value)
    fmt.Println(result)

    // The string has 3 characters.
    fmt.Println(len(result))
}700
3

`ParseInt` benchmark

Often we need to convert a string into an integer. This benchmark compares ParseInt and Atoi. It converts "1234" into an integer with each method.

Version 1 This version of the code uses the ParseInt method. It repeatedly calls ParseInt in a loop.

Version 2 Here we use the Atoi method, in a similar way as in version 1. We try to determine the time required per method call.

Result We find that the ParseInt method seems to be faster. It should be preferred when it can be used.

package main

import (
    "fmt"
    "strconv"
    "time"
)

func main() {
    t0 := time.Now()
    original := "1234";

    // Version 1: use ParseInt.
    for i := 0; i < 1000000; i++ {
        result, _ := strconv.ParseInt(original, 10, 0)
        if result != 1234 {
            return
        }
    }

    t1 := time.Now()

    // Version 2: use Atoi.
    for i := 0; i < 1000000; i++ {
        result, _ := strconv.Atoi(original)
        if result != 1234 {
            return
        }
    }

    t2 := time.Now()
    // Results of benchmark.
    fmt.Println(t1.Sub(t0))
    fmt.Println(t2.Sub(t1))
}14.023ms     ParseInt
18.5125ms    Atoi

A review

We converted strings to integers in Go. With ParseInt and the convenient method Atoi that calls ParseInt with common arguments, we perform this task with ease.

ParseInt

Other options

Example, ParseInt

Atoi

FormatInt

Itoa