How to create custom formatted output functions using fmt in Go?

To create custom formatted output functions using fmt in Go, you can define your own types and implement the fmt.Stringer interface.

Here's an example that demonstrates how to create a custom output function for a Person struct:

package main

import "fmt"

type Person struct {
    Name   string
    Age    int
    Salary float64
}

func (p Person) String() string {
    return fmt.Sprintf("Name: %s\nAge: %d\nSalary: $%.2f", p.Name, p.Age, p.Salary)
}

func main() {
    p := Person{
        Name:   "John Doe",
        Age:    30,
        Salary: 5000.0,
    }

    fmt.Println(p)
}

In this code, the Person struct implements the String() method of the fmt.Stringer interface. This method returns a formatted string representation of the Person struct.

The String() method formats the output using fmt.Sprintf(), which allows you to use placeholders (%s, %d, %f) to insert values from the struct fields.

When you call fmt.Println(p), Go's default Println() function is used, which internally calls the String() method of the fmt.Stringer interface to get the custom formatted output.