Get to know the Input Output Library in Golang

Before studying the Golang IO library, there are lots of functions in the IO library but the most important ones are 2 function interfaces, namely Reader and Writer. Reader is usually used to read data from a file or some provided input/output. Meanwhile Writer is a function that will later write data to a file or input/output provided by our system.

Reader interface

This Reader Interface has many types of function implementers, but what we will try is a reader that is taken from a file. We can see the code example below.

package main

import (
	"fmt"
	"io/ioutil"
	"log"
	"os"
)

func main() {
	f, err := os.Open("file.txt")
	if err != nil {
		log.Fatal("program broke")
	}
	defer f.Close()

	bs, err := ioutil.ReadAll(f)
	if err != nil {
		log.Fatal("program read broke")
	}

	fmt.Println(bs)
	fmt.Println(string(bs))
}

And the contents of the file.txt file are as follows

Hello World

After we look at the code above, we can imagine that os.Open is a function used to open and search for files so that later we can read the data using the ioutil.ReadAll(f) function.

If we look at the code above, the return from the ioutil.ReadAll function is captured by the variable bs which we will print and display its contents. By default, the bs variable has a data type of byte so we need to add the string(bs) function so that it can be read.

Writer interface

The Writer interface is used so that we can write to one file or several files at once. We will try to look at the code below, a basic example of using the Writer interface

package main

import (
	"log"
	"os"
)

func main() {
	dst, err := os.Create("create.txt")
	if err != nil {
		log.Fatal("program broke")
	}
	defer dst.Close()

	bs := []byte("hello world, Santekno")

	_, err = dst.Write(bs)
	if err != nil {
		log.Fatal("program broke")
	}
}

If we run the program above, a create.txt file will be created with the contents of the file in the form of the string hello world, Santekno. This program is simple where we can find out what name the file was created and what we can control the contents of the file.