This page demonstrates the usage of queues in C++ and discusses some motivation to implement it.

1. In this site I usually talk about verification and design issues. For the former usually specman is the language while for the latter VHDL, verilog or systemc are the ones.


2. Recently I started to work with a customer, that uses C++ for controlling the test bench. In one of them, I came across queues, which immediately reminded me of lists and scoreboards and its wide usage, as an important building block of any verification environment.


3. There are plenty of good examples on the web. The examples, that I saw, were simple using unsigned integers or characters. I decided to make a small exercise, using the transaction class from: producer consumer systemc example: systemc c_trans


4. The example creates a queue of c_trans transactions. The queue push command is used for data input and empty, front and pop are used for data output.
   
   #include <iostream>
   #include <queue>
   using namespace std;
   ...
   class c_trans {
     public:
     unsigned seq_n;
     unsigned data[BSZ];
     c_trans();
     c_trans(unsigned da_i[], unsigned s);
   };
   ...
     queue<c_trans> myqueue;
   
     unsigned da[BSZ]={1,2,3,4,5,6,7,8};
     const c_trans arr[2] = {c_trans(), c_trans(da, 1)};
   
     myqueue.push (arr[0]);
     myqueue.push (arr[1]);
   ...
     while (!myqueue.empty())
     {
       c_trans c = myqueue.front();
       cout << c.seq_n << " " << c.data[0] << ".. " << c.data[7] << " " << endl;
       myqueue.pop();
     }
   ...
   


5. I intend to use queues in my systemc test- benches, so I compiled it in the same way as the above mentioned systemc example.
   The full code as well as the makefile can be downloaded from: queues code .


6. In the next page . I show how to debug this simple program with gdb. As this is a simple program, it is a very good case study to see the input elements added to queue and extract using gdb commands.

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