如何在Golang中将浮点数打印为字符串而不用科学记数法

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
", 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
", v)
default:
    fmt.Printf("%v
", v)
}

Output (try it on the Go Playground):

mydata
1234567890.123000