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SystemVerilog offers much flexibility in building complicated data structures through the different types of arrays.

Static Arrays

A static array is one whose size is known before compilation time. In the example shown below, a static array of 8-bit wide is declared, assigned some value and iterated over to print its value.

module tb;
  bit [7:0]   m_data;   // A vector or 1D packed array
  initial begin
    // 1. Assign a value to the vector
    m_data = 8'hA2; 
    // 2. Iterate through each bit of the vector and print value
    for (int i = 0; i < $size(m_data); i++) begin
      $display ("m_data[%0d] = %b", i, m_data[i]);

Static arrays are further categorized into packed and unpacked arrays.

  bit [2:0][7:0]   m_data;       // Packed
  bit [15:0]     m_mem [10:0];     // Unpacked

Click here to learn more about SystemVerilog Packed Arrays !

Unpacked arrays may be fixed-size arrays, dynamic arrays, associative arrays or queues.

Click here to learn more about SystemVerilog Unpacked Arrays !

Dynamic Arrays

A dynamic array is one whose size is not known during compilation, but instead is defined and expanded as needed during runtime. A dynamic array is easily recognized by its empty square brackets [ ].

  int     m_mem [];   // Dynamic array, size unknown but it holds integer values

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Associative Arrays

An associative array is one where the content is stored with a certain key. This is easily recognized by the presence of a data type inside its square brackets [ ]. The key is represented inside the square brackets.

  int     m_data [int];       // Key is of type int, and data is also of type int
  int     m_name [string];     // Key is of type string, and data is of type int
  m_name ["Rachel"] = 30;
  m_name ["Orange"] = 2;
  m_data [32'h123] = 3333;

Click here to learn about SystemVerilog Associative Arrays !


A queue is a data type where data can be either pushed into the queue or popped from the array. It is easily recognized by the $ symbol inside square brackets [ ].

  int   m_queue [$];     // Unbound queue, no size
  m_queue.push_back(23);     // Push into the queue
  int data = m_queue.pop_front(); // Pop from the queue

Click here to learn more about SystemVerilog Queues !

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