Main and init functions in Golang

Go language has reserved two special purpose functions and those functions are main() and init() . Here are the things to know about using main() and init() functions in Golang .

main() function

In Go, the main package is a special package used with executable programs and this package contains the main() function . The main() function is a special type of function and is the entry point for executable programs. It does not take any arguments and does not return anything. Go automatically calls the main() function, so there is no need to call the main() function directly and every executable program must contain a main package and a unique main() function.

For example:

// Chương trình Go minh họa
// khái niệm của hàm main() 

// Khai báo gói chính
package main

// Nhập các gói
import (
    "fmt"
    "sort"
    "strings"
    "time"
)

// Hàm chính
func main() {

    // Sắp xếp slice đưa ra
    s := []int{345, 78, 123, 10, 76, 2, 567, 5}
    sort.Ints(s)
    fmt.Println("Sorted slice: ", s)

    // Tìm chỉ mục
    fmt.Println("Index value: ", strings.Index("Quantrimang", "ks"))

    // Tìm thời gian
    fmt.Println("Time: ", time.Now().Unix())

}

Result:

Sorted slice:  [2 5 10 76 78 123 345 567]
Index value:  3
Time:  1257894000

init() function

The init() function is just like the main function, it does not take any arguments and does not return anything. It is present in every package and is called when the package is initialized. It is implicitly declared, so you cannot reference it from anywhere and you are allowed to create multiple init() functions in the same program and they are executed in the order they are created. You are allowed to create init() functions anywhere in the program and they are called in the order of the dictionary file name (Alphabetical order). You are allowed to put statements if there is an init() function, but always remember that the init() function is executed before the main() function call, so it is independent of the main() function. The main purpose of the init() function is to initialize global variables that cannot be initialized in the global context.

For example:

// Chương trình Go minh họa
// khái niệm của hàm init() 

// Khai báo gói chính
package main

// Nhập gói
import "fmt"

// Hàm init() có nhiều nhánh
func init() {
    fmt.Println("Welcome to init() function")
}

func init() {
    fmt.Println("Hello! init() function")
}

// Hàm chính
func main() {
    fmt.Println("Welcome to main() function")
}

Result:

Welcome to init() function
Hello! init() function
Welcome to main() function