Convert float to string in go lang as per the required format

I have 4 float values(startLat,startLon,endLat,endLon)in Go. I want to append(replace) these values to the below string:

var etaString = []byte(`{"start_latitude":"` + startLat + `","start_longitude":"` + startLon + `","end_latitude":"` + endLat + `","end_longitude":"` + endLon }`)

I have to typecast them to string before doing so.

startLat := strconv.FormatFloat(o.Coordinate.Longitude, 'g', 1, 64)

However, when I do so, I get the values of these parameters as "4e+01 -1e+02 4e+01 -1e+02"
But I just want something like this: "64.2345".

How can I achieve this?

> Package strconv
>
> import "strconv" > func FormatFloat
>
> func FormatFloat(f float64, fmt byte, prec, bitSize int) string
>
> FormatFloat converts the floating-point number f to a string,
> according to the format fmt and precision prec. It rounds the result
> assuming that the original was obtained from a floating-point value of
> bitSize bits (32 for float32, 64 for float64).
>
> The format fmt is one of 'b' (-ddddp±ddd, a binary exponent), 'e'
> (-d.dddde±dd, a decimal exponent), 'E' (-d.ddddE±dd, a decimal
> exponent), 'f' (-ddd.dddd, no exponent), 'g' ('e' for large exponents,
> 'f' otherwise), or 'G' ('E' for large exponents, 'f' otherwise).
>
> The precision prec controls the number of digits (excluding the
> exponent) printed by the 'e', 'E', 'f', 'g', and 'G' formats. For 'e',
> 'E', and 'f' it is the number of digits after the decimal point. For
> 'g' and 'G' it is the total number of digits. The special precision -1
> uses the smallest number of digits necessary such that ParseFloat will
> return f exactly.

Use a precision of -1, not 1. Use a format of f, not g to avoid exponent form for large exponents (see HectorJ's comment).

startLat := strconv.FormatFloat(o.Coordinate.Longitude, 'f', -1, 64)

For example,

package main
import (
	"fmt"
	"strconv"
)
func main() {
	f := 64.2345
	s := strconv.FormatFloat(f, 'g', 1, 64)
	fmt.Println(s)
	s = strconv.FormatFloat(f, 'f', -1, 64)
	fmt.Println(s)
}

Output:

6e+01
64.2345

Some other options:

package main
import "fmt"
func main() {
   n := 64.2345
   { // example 1
      s := fmt.Sprint(n)
      fmt.Println(s == "64.2345")
   }
   { // example 2
      s := fmt.Sprintf("%v", n)
      fmt.Println(s == "64.2345")
   }
   { // example 3
      s := fmt.Sprintf("%g", n)
      fmt.Println(s == "64.2345")
   }
}

• https://golang.org/pkg/fmt#Sprint
• https://golang.org/pkg/fmt#Sprintf