Word count. Counting the words in a string can help determine if the string is appropriate for a specific usage in a program. For example, a summary may need to be a certain number of words.
In Rust, we are often focused on performance. Implementing a word counting function should use iteration over the chars in a string, and not allocate excessively.
Example program. To begin, we introduce the count_words function. This returns a usize, which is the number of words in the argument string.
Finally We test the chars for ASCII character ranges using the built-in "is_ascii" functions in Rust.
Tip A word is defined as a sequence of letters, digits and punctuation following a whitespace char.
fn count_words(s: &str) -> usize {
let mut total = 0;
let mut previous = char::MAX;
for c in s.chars() {
// If previous char is whitespace, we are on a new word.
if previous.is_ascii_whitespace() {
// New word has alphabetic, digit or punctuation start.
if c.is_ascii_alphabetic() || c.is_ascii_digit() || c.is_ascii_punctuation() {
total += 1;
}
}
// Set previous.
previous = c;
}
if s.len() >= 1 {
total += 1
}
total
}
fn main() {
let mut data = String::new();
data.push_str("cat, ");
data.push_str("bird, ");
data.push_str("and dog");
// Borrow String to call count_words.
let count = count_words(&data);
println!(" DATA: {}", data);
println!("COUNT: {}", count);
}DATA: cat, bird, and dog
COUNT: 4
Function results. In our simple example, the number of words is correctly determined. When no whitespace ends the string, it is important we add the final word to the count.
A summary. Many functions in other languages can be ported to Rust with minimal changes. The borrow checker is not involved, so memory issues are not a concern.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Mar 14, 2023 (edit).
