C++ How to access elements in a vector of queues of an object

Question

So I have a class called PCB:

class PCB
{
    private:

        int PID;
        string filename;
        int memStart;
        string cdrw;
        int filelength;

    public:

        PCB();
        PCB(int, string, int, string, int);
        virtual ~PCB();
        void getParam();
};

And I have a vector of queues: vector<queue<PCB>> printer;

How would I access the first element of the first queue in the vector? How would I use my class functions? Would it look like printer[0].getParam?

R Sahu · Accepted Answer · 2016-03-09 18:41:03Z

2

printer[0] gives you access to the first queue<PCB>.

printer[0].front() gives you access to the PCB at the front of the queue of the first queue<PCB>.

printer[0].front().getParam() allows you to call the getParam() function on the the PCB at the front of the queue of the first queue<PCB>.

answered Mar 9, 2016 at 18:41

R Sahu

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2 Comments

TheCoxer Over a year ago

Thanks man, I was thinking of that, but I wasn't super sure about how to write the syntax for that.

R Sahu Over a year ago

@TheCoxer, no problem. Glad to help.

NathanOliver · Accepted Answer · 2016-03-09 18:58:16Z

1

A std::queue only provides facilities to access the first and last items directly using front() or back(). So if you want to call a function on one of those items from the vector then you would use

std::vector<std::queue<PCB>> printer;
// fill printer
printer[0].front().getParam();
// or
printer[0].back().getParam();

In short

printer[some_index].front()
// or
printer[some_index].back()

Returns a reference to the PCB in the container at that index.

edited Mar 9, 2016 at 18:58

answered Mar 9, 2016 at 18:41

NathanOliver

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4 Comments

bdbasinger Over a year ago

What if I wanted to call two methods on the same object?

NathanOliver Over a year ago

@bdbasinger then you would use printer[some_index].front().func1; and then printer[some_index].front().func2;.

bdbasinger Over a year ago

Using .front() again wouldn’t cause it to move to the next item in the que after using it the first time?

NathanOliver Over a year ago

@bdbasinger front only gives you a reference to the first element. It does not remove anything. To remove you need to use pop.

Sudipta Kumar Sahoo · Accepted Answer · 2016-03-09 18:45:32Z

0

Here is a simple example using your code;

int main()
{
    vector<queue<PCB>> printer;

    // Create object your PCB class.
    PCB pcbObject;

    // Declare a queue
    queue<PCB> que;

    // Add the PCB class object to queue
    que.push(pcbObject);

    // Push the queue to vector.
    printer.push_back(que);

    //Get the first value
    printer[0].front().getParam();

    // Remove the element PCB
    printer[0].pop();

    return 0;
}

answered Mar 9, 2016 at 18:45

Sudipta Kumar Sahoo

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