Creating a vector of zeros for a specific size

Question

I\'d like to initialize a vector of zeros with a specific size that is determined at runtime.

In C, it would be like:

Answer 1

To initialize a vector of zeros (or any other constant value) of a given length, you can use the vec! macro:

let len = 10;
let zero_vec = vec![0; len];

That said, your function worked for me after just a couple syntax fixes:

fn zeros(size: u32) -> Vec<i32> {
    let mut zero_vec: Vec<i32> = Vec::with_capacity(size as usize);
    for i in 0..size {
        zero_vec.push(0);
    }
    return zero_vec;
}

uint no longer exists in Rust 1.0, size needed to be cast as usize, and the types for the vectors needed to match (changed let mut zero_vec: Vec<i64> to let mut zero_vec: Vec<i32>.

Answer 2

You may use resize

let mut v = Vec::new();
let l = 42;
v.resize(l, 0u32);

Answer 3

You can also use the iter::repeat function, which I suppose is "more idiomatic" (and just looks nicer to me):

use std::iter;

fn zeros(size: usize) -> Vec<i32> {
    iter::repeat(0).take(size).collect()
}

Answer 4

Here is another way, much shorter. It works with Rust 1.0:

fn zeros(size: u32) -> Vec<i32> {
    vec![0; size as usize]
}

fn main() {
    let vec = zeros(10);
    for i in vec.iter() {
        println!("{}", i)
    }
}