A package is a collection of functions and data. Use the package keyword to define a package.

is mainly used to organize Go source code, providing better reusability and readability. Since packages provide encapsulation of code, they make Go applications easy to maintain.

Create an instance of a custom package below

Create the directory pac to store the package

mkdir -p $GOPATH/src/test/pac
cd $GOPATH/src/test/pac

Create a new file pac.go

package pac

import "fmt"

func Printstr(x string) {
    fmt.Println(x + " is pac")
}

This is for ease of maintenance , make the package name and directory name consistent.

Create a new demo.go to call the customized package

Create it in the $GOPATH/src/test directory

package main

import "pac"

func main() {
    pac.Printstr("this")
}

Run

go run demo.go

Output this is pac , Proof of success

In the above example, the imported file demo.go and the package file pac.go are not in the same directory and do not belong to the same package. So how to access two files that belong to the same package and are in the same directory? See the example below.

Create pac2.go

In the $GOPATH/src/test/pac directory

package pac

import "fmt"

func printstr2 (x string)  {
    fmt.Println(x + " is pac2")
}

Modify pac.go and let pac.go call pac2.go

package pac

func Printstr(x string) {
    //fmt.Println(x + " is pac")
    printstr2(x)
}

Run demo.go

go run demo.go

Output result: this is pac2

Summary

1. If the project directory is not in the path set by the GOPATH environment variable, you need to Move the project to the GOPATH path, or set the project path in the GOPATH; otherwise it will report:

demo.go:3:8: cannot find package "pac" in any of:
    /usr/lib/golang/src/pac (from $GOROOT)
    /home/go/src/pac (from $GOPATH)

2. The import statement uses the name of the folder.

3. The first letter of the function name in the package file is capitalized so that it can be called externally. If all files in the same package access each other, it does not matter if the first letter of the function name is uppercase or lowercase.

4. The main package cannot access other files in the same directory or main package.

5. The name of the folder and the name of the package are not necessarily the same. For ease of maintenance, it is recommended to be consistent.

6. To call a custom package, use the package name and function name, as in the above example:

pac.Printstr("this")

For more related knowledge, please pay attention to the go language tutorial column

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