How to print float as string in Golang without scientific notation

Question

Suppose I have an array with 2 items whose type is string / float. How should I print them together without scientific notation for float item.

For example:

package main  import (     "fmt" )  func main() {     values := []interface{}{"mydata", 1234567890.123}     for _, v := range values{         fmt.Printf("%v\n", v)     } } 

The output will be

mydata

1.234567890123e+09

What I want is

mydata

1234567890.123

Answer 1

The package doc of fmt explains it: The %v verb is the default format, which for floating numbers means / reverts to %g which is

%e for large exponents, %f otherwise. Precision is discussed below.

If you always want "decimal point but no exponent, e.g. 123.456", use %f explicitly.

But you can only use that for floating numbers, so you have to check the type of the value you print. For that you may use a type switch or type assertion.

Example:

switch v.(type) { case float64, float32:     fmt.Printf("%f\n", v) default:     fmt.Printf("%v\n", v) } 

Output (try it on the Go Playground):

mydata 1234567890.123000 

Answer 2

You can use %f to print a float. Given your slice of interfaces, you first need to check the type of the element. You can do so as follows:

package main  import (     "fmt" )  func main() {     values := []interface{}{"mydata", 1234567890.123}     for _, v := range values {         // Check if the type conversion to float64 succeeds.         if f, ok := v.(float64); ok {             fmt.Printf("%f\n", f)         } else {             fmt.Println(v)         }     } } 

Outputs:

mydata 1234567890.123000 

The full list of flags for floats from fmt is:

%b  decimalless scientific notation with exponent a power of two,     in the manner of strconv.FormatFloat with the 'b' format,     e.g. -123456p-78 %e  scientific notation, e.g. -1.234456e+78 %E  scientific notation, e.g. -1.234456E+78 %f  decimal point but no exponent, e.g. 123.456 %F  synonym for %f %g  %e for large exponents, %f otherwise. Precision is discussed below. %G  %E for large exponents, %F otherwise