Golang: Print

Format and Print: fmt.Println

Use the package fmt

fmt.Printf("there are %v apples\n", 3)

The first argument is a string. The string can contain many special placeholder characters , starting with the percent character % (U+25: PERCENT SIGN)

2nd argument and rest arguments are used to fill the placeholders.

example:

fmt.Printf("Name is %v, Age is %v \n", "john", 36)

package main

import "fmt"

func main() {

    var x = "John"
    var y = 36

    fmt.Printf("name is %v, age is %v\n", x, y)
    // prints
    // name is John, age is 36

}

Here's the most useful placeholders:

• %v → any value. Print in human readable form.
• %#v → print in golang syntax
• %+v → if value is struct, also show the field names
• %T → type of the value
• %% → a literal percent sign

Print Line: fmt.Println

For quick printing, use

fmt.Println(v1, v2 …)

it's similar to fmt.Printf with "%v" for format.

package main

import "fmt"

func main() {

    var x = 3
    var y = 4
    fmt.Println(x, y) // 3 4
}

Format to String

To convert a value to string, use

fmt.Sprintf(string, v1, v2 …)

it return a string instead of printing.

package main

import "fmt"

func main() {

    var x = "John"
    var y = 36

    var s = fmt.Sprintf("name is %v, age is %v\n", x, y)

    fmt.Println(s == "name is John, age is 36\n") // true
}

Example: Print Type

It is very useful to print the type of a value, when learning go.

fmt.Printf("%T\n", val)

package main

import "fmt"

// using Printf to show different types of value

func main() {

    var x = 3
    fmt.Printf("%v\n", x) // 3
    fmt.Printf("%T\n", x) // int

    var x2 = 3.4
    fmt.Printf("%v\n", x2) // 3.4
    fmt.Printf("%T\n", x2) // float64

}

Example: Print Slice

[see Golang: Slice]

package main

import "fmt"

func main() {

    var sl = []int{3, 4, 5}

    // print it normally
    fmt.Printf("%v\n", sl) // [3 4 5]

    // print in golang syntax
    fmt.Printf("%#v\n", sl) // []int{3, 4, 5}

}

Example: Print Struct

• fmt.Printf("%v\n", struct) → print struct value only
• fmt.Printf("%+v\n", struct) → print both name and value
• fmt.Printf("%#v\n", struct) → print in golang syntax

package main

import "fmt"

// using print struct

func main() {

    type PP struct {
    x int
    y int
    }

    var stc = PP{1, 2}
    fmt.Printf("%T\n", stc)  // main.PP
    fmt.Printf("%v\n", stc)  // {1 2}
    fmt.Printf("%+v\n", stc) // {x:1 y:2}
    fmt.Printf("%#v\n", stc) // main.PP{x:1, y:2}
}

[see Golang: Struct]

Print String, as Bytes, Character, Codepoint

see Golang: String

Reference

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