ch2-Dynamic Arrays

2019-10-24

SystemVerilog Dynamic Array

​ A dynamic array is an unpacked array whose size can be set or changed at run time, and hence is quite different from a static array where the size is pre-determined during declaration of the array. The default size of a dynamic array is zero until it is set by the new() constructor.

Syntax

A dynamic array dimensions are specified by the empty square brackets [ ].

[data_type] [identifier_name]  [];
 
bit [7:0]   stack [];     // A dynamic array of 8-bit vector
string     names [];     // A dynamic array that can contain strings 
 

The new() function is used to allocate a size for the array and initialize its elements if required.

Dynamic Array Example

module tb;
  // Create a dynamic array that can hold elements of type int
  int   array [];       
 
  initial begin
    // Create a size for the dynamic array -> size here is 5
    // so that it can hold 5 values
    array = new [5];       
 
    // Initialize the array with five values
    array = '{31, 67, 10, 4, 99};
 
    // Loop through the array and print their values
    foreach (array[i]) 
      $display ("array[%0d] = %0d", i, array[i]);
  end
endmodule

ynamic Array Methods

Function	Description
function int size ();	Returns the current size of the array, 0 if array has not been created
function void delete ();	Empties the array resulting in a zero-sized array

module tb;
  // Create a dynamic array that can hold elements of type string
  string   fruits [];       
 
  initial begin
    // Create a size for the dynamic array -> size here is 5
    // so that it can hold 5 values
        fruits = new [3];       
 
    // Initialize the array with five values
        fruits = '{"apple", "orange", "mango"};
 
        // Print size of the dynamic array
    $display ("fruits.size() = %0d", fruits.size());
 
    // Empty the dynamic array by deleting all items
    fruits.delete();
    $display ("fruits.size() = %0d", fruits.size());
  end
endmodule

How to add new items to a dynamic array ?

​ Many times we may need to add new elements to an existing dyanmic array without losing its original contents. Since the new() operator is used to allocate a particular size for the array, we also have to copy the old array contents into the new one after creation.

int array [];
array = new [10];
 
// This creates one more slot in the array, while keeping old contents
array = new [array.size() + 1] (array);