The fmt module

The builtin fmt package provides many useful functions which are used to print to console or format to a string. Let's take a look at few of the most used functions.

fmt.Println()

fmt.Println() is the basic print function golang has to offer. It prints the values given to it seperated by commas and adds a newline at the end.

// fmt.Println() usage
fmt.Println("Hello")                            // prints "Hello"

// multiple arguments of different types can be given seperated by commas
fmt.Println("Hello", 22, 98.3, true)            // prints "Hello 22 98.3 true"

// you can also pass variables as arguments
a := "Hello"
b := "World"

fmt.Println(a, b)                               // prints "Hello World"

fmt.Printf()

fmt.Printf() is similar to printf() in C language. We give a string with keywords like %d, %v and give the other arguments which get formatted to these keywords.

// fmt.Printf() usage
fmt.Printf("%s is %d years old.", "Jon Snow", 30)   // prints "Jon Snow is 30 years old."

// using %v for printing everything
fmt.Printf("%v is %v years old.", "Jon Snow", 30)   // prints "Jon Snow is 30 years old."

// let's try printing type of any variable
name := "Jon Snow"
fmt.Printf("%T is the type of %v", name, name)      // prints "string is the type of Jon Snow"

Common keywords that are used and what variables are formatted by them

%d - integers
%s - strings
%f - floating point number
%t - boolean

%T - prints the type of the variable given
%v - prints any object of any type

fmt.Sprintf()

fmt.Sprintf() works just like fmt.Printf() but instead of printing to the console it returns the formatted string. It's highly useful for creating formatted strings from variables in golang.

Let's see the function in action.

// the function returns a formatted string.
s := fmt.Sprintf("%s is the son of %s", "Harry", "Lily")  // returns a string "Harry is the son of Lily"

// let's print the string s
fmt.Println(s)                                            // prints "Harry is the son of Lily"

The same keywords that we used for formatting in fmt.Printf() apply here too.

Exercise

Given two variables, a person's name and his favourite movie, format it and print it to console in the given format. For example the person is Nolan and his favourite movie is Tenet, your output string should be Tenet is Nolan's favourite movie. Use fmt.Printf()