golang init method

The init method in Go language is a special function used to perform initialization operations when the program is running. This article will introduce the relevant knowledge of the init method, including its characteristics, usage, etc.

1. Characteristics of the init method

1. The init method is a special method in the Go language, and its function name must be init;
2. The init method cannot be used by other functions Called, it is automatically called by the Go language runtime;
3. Multiple init methods can be defined in the same file, and they will be called sequentially in the order of definition;
4. In a package , only one init method will be executed, and it is called when the package is referenced, not when the package is compiled;
5. If the source file contains the init method, then the compiler generates the executable file They will be compiled into a file and executed in the order defined.

2. Usage of init method

1. Initialize global variables

You can initialize global variables in the init method, for example:

var (
    a int
    b bool
)

func init() {
    a = 10
    b = true
}

2. Register driver

In the Go language, it is often necessary to register the driver, for example:

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

func init() {
    sql.Register("mysql", &mysql.MySQLDriver{})
}

In the above code, use the sql.Register method to register The mysql driver is installed, so that the mysql database can be used in the program.

3. Load the configuration file

Before running the program, you need to read some parameters from the configuration file, which can be done in the init method, for example:

var config *Config

type Config struct {
    Address string
    Port    int
}

func init() {
    file, err := os.Open("config.json")
    if err != nil {
        panic(err)
    }

    decoder := json.NewDecoder(file)
    err = decoder.Decode(&config)
    if err != nil {
        panic(err)
    }
}

In the above code, the init method loads the config.json file and parses the parameters in it into the config variable.

4. Register HTTP routing

When writing web applications in Go language, it is often necessary to register HTTP routing, for example:

func init() {
    http.HandleFunc("/index", handleIndex)
}

func handleIndex(w http.ResponseWriter, r *http.Request) {
    w.Write([]byte("Hello, world!"))
}

In the above code, init The method registers the processing function handleIndex with the route /index.

5. Initialize the logger

Logging in a program is a common requirement. You can initialize a logger in the init method, for example:

var logger *log.Logger

func init() {
    file, err := os.Create("app.log")
    if err != nil {
        panic(err)
    }

    logger = log.New(file, "", log.LstdFlags)
}

In the above code, the init method creates a logger, outputs the log to the app.log file, and adds a timestamp before the log.

3. Summary

This article introduces the init method in Go language, including its characteristics, usage, etc. The existence of the init method makes the initialization operation when the program is running simpler and more flexible, making the program easier to write and maintain. Therefore, it is very important for Go language program developers to be proficient in the use of the init method.

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