Underline in Go

This is a creation in Article, where the information may have evolved or changed.

1. Underline in Import

In the Golang, import is the role of importing other package, but today in the look at the Beego framework saw the import underline, do not know its meaning, so Baidu and solution.

Import underline (e.g. Import _ Hello/imp): When importing a package, all init () functions are executed in the file under the package, however, sometimes we do not need to import the entire package, just want it to execute the init () function. You can use import to refer to the package at this time. Even if you refer to the package with the import _ package path only to invoke the Init () function, you cannot call other functions in the package by the package name.
Example:
Code structure

Main.go

package mainimport"hello/imp"func main() {    //imp.Print() //编译报错，说：undefined: imp}

Init.go

package impimport"fmt"func init() {    fmt.Println("imp-init() come here.")}func Print() {    fmt.Println("Hello!")}

Output Result:

imp-init() come here.

2. Underline in code

    package main    import (        "os"    )    func main() {        make([]byte, 1024)        f, _ := os.Open("/Users/samchen/Music/text.txt")        defer f.Close()        for {            n, _ := f.Read(buf)            if n == 0 {                break        }        os.Stdout.Write(buf[:n])    }

Explanation 1:

Underlining means ignoring this variable.

such as the OS. Open, the return value is *os. File,error

The general notation is f,err: = OS. Open (xxxxxxx)

If you do not need to know the returned error value at this time

You can use F, _: = OS. Open (XXXXXX)

This ignores the error variable

Explanation 2:

placeholder, meaning that the position should have been assigned to a value, but we do not need this value, so the value is assigned to underline, meaning that the compiler can better optimize, any type of a single value can be dropped to underline.
This is a placeholder, the method returns two results, and you want only one result, and the other uses _ placeholder, and if the variable is not used, the compiler will error.

Add:

    import"database/sql"    import"github.com/go-sql-driver/mysql"

The second import is to not use the MySQL package directly, just execute the init function of the package, register the MySQL driver into the SQL package, and then the program can use SQL packets to access the MySQL database.