队列

队列是一头取另一头存的数据结构，符合先进先出的顺序。队列像一个动态数组一样，队列长度可以增加或者减小，同时也支持在任意位置增加和移除元素。
队列声明和unpacked 数组是类似的，只是需要使用$符号来确定数组的大小。在队列中，下标0表示第一个元素，$表示最后一个entry。可以指定队列的长度，也可以不指定队列的长度。

bit    queue_1[$];     // queue of bits  (unbound queue)
int    queue_2[$];     // queue of int 
byte   queue_3[$:255]; // queue of byte (bounded queue with 256 entries)
string queue_4[$];     // queue of strings
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队列的初始化不需要像数组那样在大括号前面加’

queue_1  = {0,1,2,3}; 
queue_4  = {“Red”,"Blue”,"Green”};
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索引0表示front，最后索引表示back，push表示添加元素，pop表示移除元素。

队列方法例子

module queue;

//declaration
bit     [31:0]  queue_1[$]  ;   //unbouned queue
string          queue_2[$]  ;

initial begin
    //queue initialization
    queue_1 = {0, 1, 2, 3}  ;
    queue_2 = {"Red", "Blue", "Green"};

    //Size Method
    $display("----------Queue_1 size is %0d -----------", queue_1.size());
    foreach(queue_1[i])
        $display("\t queue_1[%0d] = %0d", i, queue_1[i]);
    $display("----------Queue_2 size is %0d -----------", queue_2.size());
    foreach(queue_2[i])
        $display("\t queue_2[%0d] = %0d", i, queue_2[i]);
    
    //insert method
    queue_2.insert(1,"Orange");
    $display("----------Queue_2 size after inserting Orange is %0d -----", queue_2.size());
    foreach(queue_2[i])
        $display("\t queue_2[%0d] = %0s", i, queue_2[i]);
    
    //delete method
    queue_2.delete(3);
    $display("---------Queue_2 size after delete is %0d ------------", queue_2.size());
    foreach(queue_2[i])
        $display("\t queue_2[%0d] = %0s", i, queue_2[i]);
end


endmodule
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输出结果是：

module queue;

//declaration
bit     [31:0]  queue_1[$]      ;
int             lvar            ;

initial begin
    //Queue initialization
    queue_1 = {0, 1, 2, 3};

    //Size-Method
    $display("\t Queue_1 size is %0d", queue_1.size());

    //Push_front Method
    queue_1.push_front(22);
    $display("\t Queue_1 size after push_front is %0d", queue_1.size());

    //Push_back Method
    queue_1.push_back(44);
    $display("\t Queue_1 size after push_back is %0d", queue_1.size());

    //pop_front Method
    lvar = queue_1.pop_front();
    $display("\t Queue_1 size after pop_front is %0d", queue_1.size());

    //pop_back Method
    lvar = queue_1.pop_back();
    $display("\t Queue_1 pop_back value is %0d", lvar);

end
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仿真结果如下：

Queue_1 size is 4
Queue_1 size after push_front is 5
Queue_1 size after push_back is 6
Queue_1 pop_front value is 22
Queue_1 pop_back value is 44
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对于bounded queue的插入操作：

module queues_array;
  //declaration
  int    queue[$:2];
  int    index;
  int  temp_var;
    
  initial begin
    //Queue Initialization:
    queue = {7,3,1};
      
    $display("Queue elements are,");
    $display("\tqueue = %p",queue);
     
    queue.push_back(10);
     
    $display("After push_back Queue elements are,");
    $display("\tqueue = %p",queue);
     
    queue.push_front(10);
     
    $display("After push_front Queue elements are,");
    $display("\tqueue = %p",queue);
  end
  
endmodule
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输出结果是：

Queue elements are,
queue = '{7, 3, 1}
After push_back Queue elements are,
queue = '{7, 3, 1}
After push_front Queue elements are,
queue = '{10, 7, 3}
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访问队列里随机一个元素

一般使用下标进行随机访问

module  queue;

//declaration
int queue[$]    ;
int index       ;
int temp_var    ;

initial begin
    //Queue Initialization
    queue = {7, 3, 0, 1, 8} ;

    $display("------- Queue elements with index ------");
    foreach(queue[i])
        $display("\t queue[%0d] = %0d", i, queue[i]);
    $display("--------------------------------------\n");

    $display("Before Queue size is %0d", queue.size());
    repeat(2) begin
        index = $urandom_range(0,4); // index of queue is from 0 to 4
        temp_var = queue[index];
        $display("Value od Index %0d in Queue is %0d", index, temp_var);
    end
    $display("After Queue size is %0d", queue.size());
end

endmodule
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其输出结果为：
任意访问需要使用队列名[索引]的方式，区别于pop方法，用索引不会删除队列元素。如果你想删除，可以队列名.delete(index)方法，通过delete方法，提供索引值就能删除。更彻底的，不加索引，队列名.delete()将会删除整个队列。