Standard package

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Standard package

Go has what is called a standard package, which has more than 100 useful functions. Prepared from the beginning You are free to use these in your program

Can output to the fmt console
math/rand Can generate random numbers
time Can process time

Package import

package main
import "fmt" //Import standard package

Import is described as "import" package name "" under "package main"

How to use the package

package main
import "fmt"
func main() {
  fmt.Println("Hello,Go")
}

//console
Hello,Go

"Fmt.Println" can display more data types than "println"

Unused packages

package main
import "fmt"
func main() {
  Println("Hello,Go") //Not using fmt package
}

//console
Error if fmt package is not used

If you are importing the fmt package but not using it, you will get an error

fmt.Printf

fmt.Printf(Format,Value used for output)

You can use the Printf function of the fmt package to specify the format and output it to the console.

The format is the shape of the output character string. Specify the format first and the value used for output second

String format

func main() {
  name := "Tanabe"
  fmt.Printf("Hello,%s", name) //%The character string contained in the variable name is used for s
}

//console
Hello,Mr. Tanabe

If you include% s in a string like "Hello,% s" The second specified character string of "fmt.Printf" is inserted in the% s part and output.

Embed multiple values

func main() {
  name := "Tanabe"
  fmt.Printf("%s, %s","Hello", name)
}

//console
Hello,Mr. Tanabe

When using% s twice, it is necessary to specify the character string to be inserted in each% s

Embed an integer

func main() {
  age := 26
  fmt.Printf("%d years old", age)
}

//console
26 years old

You can insert numbers as well as strings in the format % D in case of numerical value

Data type mismatch

func main() {
  age := "26"
  fmt.Printf("%d years old", age)
}

//console
%!d(string=26)I'm old//On the form%Error because d is used

You can insert numbers as well as strings in the format % D in case of numerical value

Difference between Printf and Println

func main() {
  fmt.Printf("Hello,% S", "Tanabe")
  fmt.Printf("Hello, %s", "Naito")
}

//console
Hello,Tanabe Hello,Mr. Naito

"Fmt.Printf" is different from "fmt.Println" Does not start a new line after the output string

func main() {
  fmt.Printf("Hello, %s\n", "Tanabe")
  fmt.Printf("Hello, %s\n", "Naito")
}

//console
Hello,Mr. Tanabe
Hello,Mr. Naito

If you use \ n in a string, the output string will break.

\n(2)

func main() {
  name := "Tanabe"
  fmt.Printf("Hello, \n%s" name) //In the text\Include n
}

//console
Hello,
Mr. Tanabe

If you include it in the middle of the string, the character following \ n will be broken and output to the next line.

Go language-standard package

Standard package