Tuples and text

Now that we’ve gone over the basic types, you might have wondered about a detail in the hello_user.zig file: What’s that .{} symbol in the call to the print function?

std.debug.print("\nHello, user.\n", .{});

That’s a data structure called a tuple. Specifically, .{} is an empty tuple.

The print function expects a tuple as its second argument. It doesn’t have to be empty. A tuple is a simple data structure that can also hold multiple values at once. We could have something like this with a value:

hello_user_2.zig

const std = @import("std");

pub fn main() void {

const s_name = "Programmer";

std.debug.print(

\\Hello, {s},

\\I was waiting for you.

, .{s_name});

}

$ zig run hello_user_2.zig

Hello, Programmer

I was waiting for you.

You can use your own name as the value of the s_name string instead of "Programmer".

This time, the string we wrote starts with a double backslash \\ and spans multiple lines. That means it's a multiline string, and the line breaks are included automatically with each new line.

As you can see, the string \\Hello, {s}, now also contains {s}. This symbol tells Zig to insert a value from the tuple.

{s} means that the value is a string (the s stands for string). If the value were a number, we couldn't use {s} as the placeholder - we'd need a different letter, such as {d} (where d stands for decimal).

We could also pass more data in the tuple:

hello_user_3.zig

const std = @import("std");

pub fn main() void {

const s_name = "Programmer";

const n_age = 20;

std.debug.print("\nHello, {s}.\nYou are {b} years old.\n", .{ s_name, n_age });

}

$ zig run hello_user_3.zig

Hello, Programmer.

You are 10100 years old.

10100 years?

Why do we get that output if n_age has the value 20? Take your time to think about it.

Notice that we’re using the insertion placeholder {b}. What could that b mean for 20 to turn into 10100?

Data Formats in a String

Here’s a table of these placeholders to help you out:

{s}	Text string: "Hello", "Programmer"
{d}	Number printed in decimal format: 1, 3, 42, 23, etc.
{b}	Number printed in binary: 0001, 0010…
{x}	Number printed in lowercase hexadecimal: 255 as ff
{X}	Number printed in uppercase hexadecimal: 255 as FF
{c}	A character (such as a u8 interpreted as ASCII): 97 is 'a'
{}	Zig will try to detect the type

As you may have figured out, {b} means the number passed in the tuple will be printed in binary format in the string.

If we use {} or {d}, the result will be printed in the decimal format we’re used to:

hello_user_4.zig

const std = @import("std");

pub fn main() void {

const s_name = "Programmer";

const n_age = 20;

std.debug.print("\nHello, {s}.\nYou are {d} years old.\n", .{ s_name, n_age });

}

$ zig run hello_user_4.zig

Hello, Programmer.

You are 20 years old.