How do I allocate an array at runtime in Rust?

Question

Once I have allocated the array, how do I manually free it? Is pointer arithmetic possible in unsafe mode?

Like in C++:

double *A=new double[1000];
double *p=A;
int i;
for(i=0; i<1000; i++)
{
     *p=(double)i;
      p++;
}
delete[] A;

Is there any equivalent code in Rust?

Answer 1

Based on your question, I'd recommend reading the Rust Book if you haven't done so already. Idiomatic Rust will almost never involve manually freeing memory.

As for the equivalent to a dynamic array, you want a vector. Unless you're doing something unusual, you should avoid pointer arithmetic in Rust. You can write the above code variously as:

// Pre-allocate space, then fill it.
let mut a = Vec::with_capacity(1000);
for i in 0..1000 {
    a.push(i as f64);
}

// Allocate and initialise, then overwrite
let mut a = vec![0.0f64; 1000];
for i in 0..1000 {
    a[i] = i as f64;
}

// Construct directly from iterator.
let a: Vec<f64> = (0..1000).map(|n| n as f64).collect();