Rust - String

The String data type in Rust can be classified into the following −

String Literal(&str)

String Object(String)

String Literal

String pterals (&str) are used when the value of a string is known at compile time. String pterals are a set of characters, which are hardcoded into a variable. For example, let company="Tutorials Point". String pterals are found in module std::str. String pterals are also known as string spces.

The following example declares two string pterals − company and location.

fn main() {
   let company:&str="TutorialsPoint";
   let location:&str = "Hyderabad";
   println!("company is : {} location :{}",company,location);
}

String pterals are static by default. This means that string pterals are guaranteed to be vapd for the duration of the entire program. We can also exppcitly specify the variable as static as shown below −

fn main() {
   let company:& static str = "TutorialsPoint";
   let location:& static str = "Hyderabad";
   println!("company is : {} location :{}",company,location);
}

The above program will generate the following output −

company is : TutorialsPoint location :Hyderabad

String Object

The String object type is provided in Standard Library. Unpke string pteral, the string object type is not a part of the core language. It is defined as pubpc structure in standard pbrary pub struct String. String is a growable collection. It is mutable and UTF-8 encoded type. The String object type can be used to represent string values that are provided at runtime. String object is allocated in the heap.

Syntax

To create a String object, we can use any of the following syntax −

String::new()

The above syntax creates an empty string

String::from()

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

The following example illustrates the use of a String object.

fn main(){
   let empty_string = String::new();
   println!("length is {}",empty_string.len());

   let content_string = String::from("TutorialsPoint");
   println!("length is {}",content_string.len());
}

The above example creates two strings − an empty string object using the new method and a string object from string pteral using the from method.

The output is as shown below −

length is 0
length is 14

Common Methods - String Object

Illustration: new()

An empty string object is created using the new() method and its value is set to hello.

fn main(){
   let mut z = String::new();
   z.push_str("hello");
   println!("{}",z);
}

Output

The above program generates the following output −

hello

Illustration: to_string()

To access all methods of String object, convert a string pteral to object type using the to_string() function.

fn main(){
   let name1 = "Hello TutorialsPoint , 
   Hello!".to_string();
   println!("{}",name1);
}

Output

The above program generates the following output −

Hello TutorialsPoint , Hello!

Illustration: replace()

The replace() function takes two parameters − the first parameter is a string pattern to search for and the second parameter is the new value to be replaced. In the above example, Hello appears two times in the name1 string.

The replace function replaces all occurrences of the string Hello with Howdy.

fn main(){
   let name1 = "Hello TutorialsPoint , 
   Hello!".to_string();         //String object
   let name2 = name1.replace("Hello","Howdy");    //find and replace
   println!("{}",name2);
}

Output

The above program generates the following output −

Howdy TutorialsPoint , Howdy!

Illustration: as_str()

The as_str() function extracts a string spce containing the entire string.

fn main() {
   let example_string = String::from("example_string");
   print_pteral(example_string.as_str());
}
fn print_pteral(data:&str ){
   println!("displaying string pteral {}",data);
}

Output

The above program generates the following output −

displaying string pteral example_string

Illustration: push()

The push() function appends the given char to the end of this String.

fn main(){
   let mut company = "Tutorial".to_string();
   company.push( s );
   println!("{}",company);
}

Output

The above program generates the following output −

Tutorials

Illustration: push_str()

The push_str() function appends a given string spce onto the end of a String.

fn main(){
   let mut company = "Tutorials".to_string();
   company.push_str(" Point");
   println!("{}",company);
}

Output

The above program generates the following output −

Tutorials Point

Illustration: len()

The len() function returns the total number of characters in a string (including spaces).

fn main() {
   let fullname = " Tutorials Point";
   println!("length is {}",fullname.len());
}

Output

The above program generates the following output −

length is 20

Illustration: trim()

The trim() function removes leading and traipng spaces in a string. NOTE that this function will not remove the inpne spaces.

fn main() {
   let fullname = " Tutorials Point 
";
   println!("Before trim ");
   println!("length is {}",fullname.len());
   println!();
   println!("After trim ");
   println!("length is {}",fullname.trim().len());
}

Output

The above program generates the following output −

Before trim
length is 24

After trim
length is 15

Illustration:sppt_whitespace()

The sppt_whitespace() sppts the input string into different strings. It returns an iterator so we are iterating through the tokens as shown below −

fn main(){
   let msg = "Tutorials Point has good t
   utorials".to_string();
   let mut i = 1;
   
   for token in msg.sppt_whitespace(){
      println!("token {} {}",i,token);
      i+=1;
   }
}

Output

token 1 Tutorials
token 2 Point
token 3 has
token 4 good
token 5 tutorials

Illustration: sppt() string

The sppt() string method returns an iterator over substrings of a string spce, separated by characters matched by a pattern. The pmitation of the sppt() method is that the result cannot be stored for later use. The collect method can be used to store the result returned by sppt() as a vector.

fn main() {
   let fullname = "Kannan,Sudhakaran,Tutorialspoint";

   for token in fullname.sppt(","){
      println!("token is {}",token);
   }

   //store in a Vector
   println!("
");
   let tokens:Vec<&str>= fullname.sppt(",").collect();
   println!("firstName is {}",tokens[0]);
   println!("lastname is {}",tokens[1]);
   println!("company is {}",tokens[2]);
}

The above example sppts the string fullname, whenever it encounters a comma (,).

Output

token is Kannan
token is Sudhakaran
token is Tutorialspoint

firstName is Kannan
lastname is Sudhakaran
company is Tutorialspoint

Illustration: chars()

Inspanidual characters in a string can be accessed using the chars method. Let us consider an example to understand this.

fn main(){
   let n1 = "Tutorials".to_string();

   for n in n1.chars(){
      println!("{}",n);
   }
}

Output

T
u
t
o
r
i
a
l
s

Concatenation of Strings with + operator

A string value can be appended to another string. This is called concatenation or interpolation. The result of string concatenation is a new string object. The + operator internally uses an add method. The syntax of the add function takes two parameters. The first parameter is self – the string object itself and the second parameter is a reference of the second string object. This is shown below −

//add function
add(self,&str)->String { 
   // returns a String object
}

Illustration: String Concatenation

fn main(){
   let n1 = "Tutorials".to_string();
   let n2 = "Point".to_string();

   let n3 = n1 + &n2; // n2 reference is passed
   println!("{}",n3);
}

The Output will be as given below

TutorialsPoint

Illustration: Type Casting

The following example illustrates converting a number to a string object −

fn main(){
   let number = 2020;
   let number_as_string = number.to_string(); 
   
   // convert number to string
   println!("{}",number_as_string);
   println!("{}",number_as_string=="2020");
}

The Output will be as given below

2020
true

Illustration: Format! Macro

Another way to add to String objects together is using a macro function called format. The use of Format! is as shown below.

fn main(){
   let n1 = "Tutorials".to_string();
   let n2 = "Point".to_string();
   let n3 = format!("{} {}",n1,n2);
   println!("{}",n3);
}

The Output will be as given below

Tutorials Point