#
In queues size is flexible. It can change easily
- Variable size array with automatic sizing, single dimension
- Many searching, sorting, and insertion methods
- Constant time to read, write, and insert at front & back
- Out of bounds access causes run-time error
A Queue is a variable size ordered collection of homogeneous objects. There are two main aspects of a queue that makes it attractive for verification purposes. First, a queue can have variable length, including a length of zero. This makes a queue an ideal candidate as a storage element that can shrink or grow as elements are deleted or added to it without fixing an artificial upper limit on its size as a regular fixed size array. The other advantage of having a queue is that, it provides a way to emulate both Last In
First Out (LIFO) and First In First Out (FIFO) behavior that are required in so many ordered transactions. At the same time a queue still allows you to access any element randomly within the queue without any overhead just as a regular array. A Queue is analogous to one dimensional unpacked array that grows and shrinks automatically. Queues are declared using the same syntax as unpacked arrays, but specifying ‘$’ as the array size.
Eg:
1.byte q1 [$];
2.integer my_q[$] = {1, 3, 5};
3.string names [$] = {“Ram, Sham, Laxman”};
4.
5.bit q [$:255];
6.// A queue whose maximum size is 256 bits.
Example :
01.module example ;
02.
03.int int_queue[$] = { 1, 2, 3 };
04.string string_queue [$] = {"first","second","third","forth"};
05.
06.string s;
07.
08.initial
09.begin
10.// example of the use of size
11.$display("\n Use of size()");
12.
13.for (int i = 0 ; i < int_queue.size(); i++ )
14.$display(int_queue[i]);
15.
16.$display("\n\n Elements of string_queue[$]");
17.for (int i = 0; i < string_queue.size; i++)
18.$write(string_queue[i]," ");
19.
20.// example of the use of insert
21.string_queue.insert(1,"next"); // former element 1 is now element 2.
22.string_queue.insert(2,"somewhere");
23.
24.$display("\n\n Use of insert()");
25.for (int i = 0; i < string_queue.size; i++)
26.$write(string_queue[i]," ");
27.
28.// example of the use of delete
29.string_queue.delete(1); // delete the element
30.string_queue.delete(3);
31.
32.$display("\n\n Use of delete()");
33.for (int i = 0; i < string_queue.size; i++)
34.$write(string_queue[i]," ");
35.
36.// example of the use of pop_front
37.// deletes the front of the queue
38.s = string_queue.pop_front();
39.$display("\n\n Use of pop_front()");
40.$display(" %s",s);
41.
42.for (int i = 0; i < string_queue.size; i++)
43.$write(string_queue[i]," ");
44.
45.// example of the use of pop_back
46.// deletes the back of the queue
47.s = string_queue.pop_back();
48.$display("\n\n Use of pop_back()");
49.$display(" %s",s);
50.for (int i = 0; i < string_queue.size; i++)
51.$write(string_queue[i]," ");
52.
53.// example of the use of push_front and push_back
54.// grows the queue
55.string_queue.push_front("in-front");
56.string_queue.push_back("in-back");
57.
58.$display("\n\n Use of push_front() and push_back()");
59.for (int i = 0; i < string_queue.size; i++)
60.$write(string_queue[i]," \n ");
61.
62.end
63.endmodule
Output : #
01.#
02.# Use of size()
03.# 1
04.# 2
05.# 3
06.#
07.#
08.# Elements of string_queue[$]
09.# first second third forth
10.#
11.# Use of insert()
12.# first next somewhere second third forth
13.#
14.# Use of delete()
15.# first somewhere second forth
16.#
17.# Use of pop_front()
18.# first
19.# somewhere second forth
20.#
21.# Use of pop_back()
22.# forth
23.# somewhere second
24.#
25.# Use of push_front() and push_back()
26.# in-front
27.# somewhere
28.# second
29.# in-back
30.#
31.<p> </p>
