Dynamic Arrays

What is a Dynamic Array? #

A Dynamic Array is a one-dimensional unpacked array whose size can be set and changed during simulation runtime using the new[] operator.

Unlike fixed arrays, dynamic arrays are ideal when the number of elements is not known in advance, such as in packet-based verification scenarios where the size can vary with each transaction.

Syntax:

data_type array_name[];
array_name = new[size];         // Allocates memory for given size

Example: Declaration and Initialization

module example;
  int dyn_array[];               // Declare a dynamic array
  dyn_array = new[5];            // Allocate 5 elements

  foreach (dyn_array[i])
    dyn_array[i] = i * 10;       // Initialize values: 0, 10, 20, 30, 40
endmodule

Built-in Methods

Resizing Dynamic Arrays

You can resize a dynamic array at runtime:

dyn_array = new[20];              // Resize with data loss
dyn_array = new[10](dyn_array);   // Resize and keep old values

If you don’t use (old_array) during resizing, previous values are discarded.

Deleting a Dynamic Array

dyn_array.delete();               // Clears all elements

After deletion:

• Array size becomes 0
• Memory is released

Example:

module test;
  int dyn_array[];

  initial begin
    dyn_array = new[4];             // Allocate 4 elements
    foreach (dyn_array[i])
      dyn_array[i] = i + 1;

    $display("Original size: %0d", dyn_array.size());  

    dyn_array = new[8](dyn_array);  // Resize and keep old values
    dyn_array[4] = 5;
    dyn_array[5] = 6;

    $display("Resized size: %0d", dyn_array.size());   

    dyn_array.delete();             // Free memory
    $display("After delete: %0d", dyn_array.size());   
  end
endmodule

Output:

Original size: 4
Resized size:  8
After delete:  0

Comparison: Dynamic vs Fixed Arrays