Understanding Print function in Go (Golang)

Overview

Print is defined in the fmt package and is used to format a string and write to standard output

https://golang.org/pkg/fmt/#Print

Below is the function prototype of Print

func Print(a ...interface{}) (n int, err error)

Print formats the string using the default format specifier but does not add a new line after the string. Print takes a variable number of arguments where each argument is an empty interface. It returns the number of characters printed and any error if happens. Since the argument type is an empty interface we can pass any data type to it. We can pass a string, int, float, struct, or any other data type. Each of the arguments to the Print function is formatted according to the default format specifier of that argument type. For example, the struct will be formatted according to the below specifier

%v

This format specifier only prints the Value part in the struct. There is also one more function provided by fmt package which appends a new line – Println. The Print function is exactly the same as the Println function other than two differences

• It does not append a newline at the end. We need to use the new line identifier to add a new line “\n”.

• Space is only added between the arguments if neither of the operands is a string

Let’s see an example

Program

Let’s see an example for the same

package main
import "fmt"
type employee struct {
Name string
Age int
}
func main() {
name := "John"
age := 21
fmt.Print("Name is:", name, "\n")
fmt.Print("Age is:", age, "\n")
e := employee{
Name: name,
Age: age,
}
fmt.Print(e, "\n")
fmt.Print("a", 12, "b", 12.0, "\n")
fmt.Print(12, 12.0, "\n")
bytesPrinted, err := fmt.Print("Name is: ", name, "\n")
if err != nil {
log.Fatalln("Error occured", err)
}
fmt.Print(bytesPrinted)
}

Output

Name is:John
Age is:21
{John 21}
a12b12
12 12
Name is: John
14

Some important points to note about the Print function

• It does not append a new line at the end. That is why need to use “\n” for adding a new line.

• It only adds space between two arguments if each of them is a non-string. That is why

fmt.Print(12, 12.0, "\n")

prints

12 12

while

fmt.Print("a", 12, "b", 12.0, "\n")

prints

a12b12

• It also returns the number of characters printed and any error if happens

bytesPrinted, err := fmt.Print("Name is: ", name, "\n")
if err != nil {
log.Fatalln("Error occured", err)
}
fmt.Print(bytesPrinted)

will output below

Name is: John
14

The number of bytesPrinted is 14 as 14 characters are outputted

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