Go fmt.Printf String Formatting

Go Language Basic Syntax

Go can use fmt.Printf to format strings, as follows:

fmt.Printf(format string, args ...interface{})

• Format String: A string containing format specifiers starting with %, such as %s for string and %d for decimal integer.

• Argument List: Multiple arguments separated by commas, must correspond in number to the format specifiers, otherwise an error will occur at runtime.

Example

package main

import (
   "fmt"
   "strings"
)

func main() {
  name := "John Doe"
  age := 27

  // Print string in lowercase
  fmt.Printf("hello, %s\n", name)

  // Print string in uppercase
  fmt.Printf("hello, %s\n", strings.ToUpper(name))

  // Print age as a decimal number
  fmt.Printf("%s is %d years old\n", name, age)

  // Print age as a floating-point number with two decimal places
  fmt.Printf("%s is %.2f years old\n", name, age)
}

Output:

hello, John Doe
hello, JOHN DOE
John Doe is 27 years old
John Doe is %!f(int=27) years old

Go String Format Specifiers:

Example

package main

import (
    "fmt"
    "os"
)

type point struct {
    x, y int
}

func main() {

    p := point{1, 2}
    fmt.Printf("%v\n", p)

    fmt.Printf("%+v\n", p)

    fmt.Printf("%#v\n", p)

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

    fmt.Printf("%t\n", true)

    fmt.Printf("%d\n", 123)

    fmt.Printf("%b\n", 14)

    fmt.Printf("%c\n", 33)

    fmt.Printf("%x\n", 456)

    fmt.Printf("%f\n", 78.9)

    fmt.Printf("%e\n", 123400000.0)
    fmt.Printf("%E\n", 123400000.0)

    fmt.Printf("%s\n", "\"string\"")

    fmt.Printf("%q\n", "\"string\"")

    fmt.Printf("%x\n", "hex this")

    fmt.Printf("%p\n", &p)

    fmt.Printf("|%6d|%6d|\n", 12, 345)

    fmt.Printf("|%6.2f|%6.2f|\n", 1.2, 3.45)

    fmt.Printf("|%-6.2f|%-6.2f|\n", 1.2, 3.45)

    fmt.Printf("|%6s|%6s|\n", "foo", "b")

    fmt.Printf("|%-6s|%-6s|\n", "foo", "b")

    s := fmt.Sprintf("a %s", "string")
    fmt.Println(s)

    fmt.Fprintf(os.Stderr, "an %s\n", "error")
}

Output:

{1 2}
{x:1 y:2}
main.point{x:1, y:2}
main.point
true
123
1110
!
1c8
78.900000
1.234000e+08
1.234000E+08
"string"
"\"string\""
6865782074686973

0xc0000b4010 | 12| 345| | 1.20| 3.45| |1.20 |3.45 | | foo| b| |foo |b | a string an error ```

Go Language Basic Syntax