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Introduction to Strings

  • What are Strings?

Strings are a sequence of Unicode characters. In Rust, a String is not null-terminated unlike strings in other programming languages. They can contain null characters.

Note: Have a look at the unicode characters

Types of Strings

  • Strings are of two types: &str and String
    • String Literal (&str)
  • A String literal has the following properties:
    • Primitive type
    • Immutable
    • Fixed-length string stored somewhere in memory
    • Value of string is known at compile time

Note: A String literal is also known as a String slice.

Create a String Literal

The following illustration shows how to create a primitive string:

fn main() {
  //define a primitive String variable
  let language:&str = "Rust";
  //print the String literal
  println!("String literal: {}", language);
  //print the length of the String literal
  println!("Length of the string literal: {}", language.len());


String literal: Rust
Length of the string literal: 4

String Object (String)

  • A String object has the following properties:
    • A string is encoded as a UTF-8 sequence
    • Heap-allocated data structure
    • The size of this string can be modified
    • Not null-terminated
    • Encode string values that are given at the run time

Create a String Object

There are many different ways to create and manipulate String objects. We will discuss two here.

Creating an Empty String Object

This method converts the empty String or a String literal to a String object using the .tostring method.

The following illustration creates an empty String and then converts into the string object using the .to_string() method.

Creating an Initialized String Object

This method creates a string with some default value passed as an argument to the from() method.

The following illustration creates a String literal and then converts it into the String object.


fn main() {
  // create an empty String
  let course1 = String::new();
  // convert String literal to String object using .to_string
  let s_course1 = course1.to_string();
  // print the String object
  println!("This is an empty string {}.", s_course1);
  // print the length of an empty String  object
  println!("This is a length of my empty string {}.", s_course1.len());

  // create a String literal
  let course2 = "Rust Programming";
  // convert String literal to string object using .to_string
  let s_course2 = course2.to_string();
  // print the String object
  println!("This is a string literal : {}.", s_course2);
  // print the length of a String object
  println!("This is a length of my string literal {}.", s_course2.len());

  // define a String object using from method
  let course3 = String::from("Rust Language");
  // print the String object
  println!("This is a string object : {}.", course3);
  // print the length of an string object
  println!("This is the length of my string object {}.", course3.len());

Note: len() is a built-in function used to find the length of a String literal and String object.