Golang Example - strconv FormatInt Function Guide

Golang Example - strconv FormatInt Function Guide

Learn strconv FormatInt Function with examples in the Go Language.

golang strconv FormatInt function

strconv is a standard package in go language that provides various function implementations for converting a string to types into an int, float, boolean, etc.

FormatInt is one of the important functions that is used to convert the Integer type to the String type. You can check official documentation is herešŸ”—

Here is the syntax of this function

func FormatInt(input int64, base int) string

Argument list:

input is a numeric integer value of type int64 only

the base is int arguments that are valid values from 2 to 36.

Return type:

The string value is returned which contains a numeric value.

Function Syntax

FormatInt() function accepts and parse integer type and convert based on the base value, returning a string type value.

if the base value is less than equal to 2 ie 1,0 or negative number, It throws runtime error - panic: strconv: illegal AppendInt/FormatInt base

Complete Stack trace

panic: strconv: illegal AppendInt/FormatInt base

goroutine 1 [running]:
strconv.formatBits(0x0, 0x0, 0x0, 0x46e, 0x1, 0x65514b0fc43a0000, 0xc000069eb0, 0x8, 0x10, 0xc0000341c0, ...)
        A:/Golang/src/strconv/itoa.go:91 +0x51c
strconv.FormatInt(0x46e, 0x1, 0x9, 0xc000048238)
        A:/Golang/src/strconv/itoa.go:29 +0xd2
main.main()
        A:/Golang/work/Test.go:12 +0x4c
exit status 2

if the base value is greater than 2, It converts the integer to String binary which contains 0 and 1 only

s0 := strconv.FormatInt(55, 2)
fmt.Printf("type=%T, output=%v\n", s0, s0) //type=string, output=110111

if the base value is greater than equal to 10, the output contains lower case characters ā€˜aā€™ to ā€˜zā€™ which is of the hexadecimal number in a string representation

s0 := strconv.FormatInt(1234, 16)
 fmt.Printf("type=%T, output=%v\n", s0, s0) //type=string, output=46e

How to convert Integer to String using Strconv FormatInt Example in Golang

Here is an example of converting Integer to different string numeric values

package main

import (
    "fmt"
    "strconv"
)

func main() {
    input: = int64(1134)
    fmt.Printf("type=%T, output=%v\n", input, input)
    s0: = strconv.FormatInt(input, 2)
    fmt.Printf("type=%T, output=%v\n", s0, s0)
    s1: = strconv.FormatInt(input, 10)
    fmt.Printf("type=%T, output=%v\n", s1, s1)
    s2: = strconv.FormatInt(input, 16)
    fmt.Printf("type=%T, output=%v\n", s2, s2)

}

Output:

type=int64, output=1134  
type=string, output=10001101110  
type=string, output=1134  
type=string, output=46e

Convert integer types - Int8,Int16,Int 32 to String

FormatInt always returns the Int64 value. With int64(int8 value) code, returned Int64 value is converted to string type. Likewise, Int16(),Int32() are used to converted to Int16, Int32 types. Here is an example program to convert to other types if FormatInt accepts value other than Int64 type, It throws compilation error - cannot use input1 (type int8) as type int64 in argument to strconv.FormatInt

input1 := int8(20)
fmt.Printf("type=%T, output=%v\n", input1, input1)
s0 := strconv.FormatInt(input1, 10)

output

# command-line-arguments
.\Test.go:14:25: cannot use input1 (type int8) as type int64 in argument to strconv.FormatInt

The same error occurs for other types Int16 and Int32, Here is an error case.

func main() {
    input1: = int8(34)
    input2: = int16(134)
    input3: = int32(1134)
    fmt.Printf("type=%T, output=%v\n", input1, input1)
    s0: = strconv.FormatInt(input1, 10)
    fmt.Printf("type=%T, output=%v\n", input2, input2)
    s1: = strconv.FormatInt(input2, 10)
    fmt.Printf("type=%T, output=%v\n", s1, s1)
    s2: = strconv.FormatInt(input3, 10)
    fmt.Printf("type=%T, output=%v\n", s2, s2)

}

Output:

.\Test.go:14:25: cannot use input1 (type int8) as type int64 in argument to strconv.FormatInt
.\Test.go:16:25: cannot use input2 (type int16) as type int64 in argument to strconv.FormatInt
.\Test.go:18:25: cannot use input3 (type int32) as type int64 in argument to strconv.FormatInt

FormatInt accepts Int64 value only, we need to convert Int8, Int16, Int32 to Int64 types. Followings a complete example

package main

import (
    "fmt"
    "strconv"
)

func main() {
    input1: = int8(34)
    input2: = int16(134)
    input3: = int32(1134)
    fmt.Printf("type=%T, output=%v\n", input1, input1)
    s0: = strconv.FormatInt(int64(input1), 10)
    fmt.Printf("type=%T, output=%v\n", s0, s0)
    s1: = strconv.FormatInt(int64(input2), 10)
    fmt.Printf("type=%T, output=%v\n", s1, s1)
    s2: = strconv.FormatInt(int64(input3), 10)
    fmt.Printf("type=%T, output=%v\n", s2, s2)

}

Output:

type=int8, output=34  
type=string, output=34  
type=string, output=134  
type=string, output=1134