Go language variable scope

The scope is the scope of the constant, type, variable, function or package represented by the declared identifier in the source code.

Variables in Go language can be declared in three places:

• Variables defined in a function are called local variables
• Variables defined outside the function are called global variables
• Variables in a function definition are called formal parameters

Next, let's learn about local variables, global variables and formal parameters.

local variable

Variables declared in the function body are called local variables. Their scope is only in the function body, and parameters and return value variables are also local variables.

In the following example, the main() function uses local variables a, b, c:

//10scopeRules.go
package main

import "fmt"

func main() {
	//Declare local variables
	var a, b, c int
	
	//Initialization parameters
	a = 10
	b = 20
	c = a + b
	
	fmt.Printf ("result: a = %d, b = %d and c = %d\n", a, b, c)
}

Operation results:

global variable

Variables declared outside the function are called global variables. Global variables can be used in the whole package or even external packages (after being exported).

Global variables can be used in any function. The following example demonstrates how to use global variables:

//10scopeRules2.go
package main

import "fmt"

//Declare global variables
var g int

func main() {
	//Declare local variables
	var a, b int
	
	//Initialization parameters
	a = 10
	b = 20
	g = a + b
	
	fmt.Printf ("result: a = %d, b = %d and g = %d\n", a, b, g)
}

Operation results:

In Go language programs, the names of global variables and local variables can be the same, but local variables in functions will be given priority. Examples are as follows:

//10scopeRules3.go
package main

import "fmt"

//Declare global variables 
var g int = 20

func main() {
	//Declare local variables
	var g int = 10
	
	fmt.Printf ("result: g = %d\n", g)
}

Operation results:

Formal parameters

Formal parameters are used as local variables of the function. Examples are as follows:

//10scopeRules4.go
package main

import "fmt"

//Declare global variables 
var a int = 20

func main() {
	//Declare local variables in main function
	var a int = 10
	var b int = 20
	var c int = 0
	
	fmt.Printf("main()In function a = %d\n",  a);
	c = sum(a, b)
	fmt.Printf("main()In function c = %d\n",  c);
}

//Function definition - adding two numbers
func sum(a, b int) int {
	fmt.Printf("sum() In function a = %d\n",  a);
	fmt.Printf("sum() In function b = %d\n",  b);
	return a + b
}
	

Operation results:

Initialize local and global variables

The default values of different types of local and global variables are:

Reference: https://www.w3cschool.cn/go/