Convert a float64 to an int in Go

Question

How does one convert a float64 to an int in Go  I know the strconv package can be used to convert anything to or from a string  but not between data types where one isn t a string  I know I can use fmt Sprintf to convert anything to a string  and then strconv it to the data type I need  but this extra conversion seems a bit clumsy - is there a better way to do this

User · Answer

Simply casting to an int truncates the float, which if your system internally represent 2.0 as 1.9999999999, you will not get what you expect. The various printf conversions deal with this and properly round the number when converting. So to get a more accurate value, the conversion is even more complicated than you might first expect:

package main

import (
    "fmt"
    "strconv"
)

func main() {
    floats := []float64{1.9999, 2.0001, 2.0}
    for _, f := range floats {
        t := int(f)
        s := fmt.Sprintf("%.0f", f)
        if i, err := strconv.Atoi(s); err == nil {
            fmt.Println(f, t, i)
        } else {
            fmt.Println(f, t, err)
        }
    }
}

Code on Go Playground

User · Answer

package main import  fmt  func main       var x float64   5 7   var y int   int x    fmt Println y      outputs  5

User · Answer

Correct rounding is likely desired    Therefore math Round   is your quick    friend  Approaches with fmt Sprintf and strconv Atois   were 2 orders of magnitude slower according to my tests with a matrix of float64 values that were intended to become correctly rounded int values   package main import        fmt       math    func main         var x float64   5 51     var y float64   5 50     var z float64   5 49     fmt Println int math Round x        outputs  6      fmt Println int math Round y        outputs  6      fmt Println int math Round z        outputs  5      math Round   does return a float64 value but with int   applied afterwards  I couldn t find any mismatches so far

User · Answer

If its simply from float64 to int  this should work  package main  import        fmt     func main         nf      float64 -1 9999  -2 0001  -2 0  0  1 9999  2 0001  2 0         round     fmt Printf  Round          for    f    range nf           fmt Printf   d    round f             fmt Printf   n          rounddown ie  math floor     fmt Printf  RoundD         for    f    range nf           fmt Printf   d    roundD f             fmt Printf   n          roundup ie  math ceil     fmt Printf  RoundU         for    f    range nf           fmt Printf   d    roundU f              fmt Printf   n       func roundU val float64  int       if val  gt  0   return int val 1 0        return int val     func roundD val float64  int       if val  lt  0   return int val-1 0        return int val     func round val float64  int       if val  lt  0   return int val-0 5        return int val 0 5      Outputs   Round   -2 -2 -2 0 2 2 2  RoundD  -2 -3 -3 0 1 2 2  RoundU  -1 -2 -2 0 2 3 3    Here s the code in the playground - https   play golang org p HmFfM6Grqh

User · Answer

You can use int   function to convert float64 type data to an int  Similarly you can use float64    Example   func check n int  bool           count the number of digits      var l int   countDigit n      var dup int   n      var sum int   0          calculates the sum of digits         raised to power      for dup  gt  0              sum    int math Pow float64 dup   10   float64 l               dup    10              return n    sum

[go] Convert a float64 to an int in Go

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