Removing strings from a STL Set container in a virtual function: User Input Problem

[daniel88]

Hi guys,

I am bringing a problem which I thought I had solved, but it has re-reared its ugly head. The problem is one of user input (I can hear you veterans audibly say "Aargh!"). I wish to remove serial numbers (of type string) from a set. To give you a little context, I am working on a Point-of-Sale system. This function allows the user to specify the serial numbers of itemized products that have been sold and are thus no longer part the inventory. I got what seemed like a perfect solution to this problem on this forum, but for some reason in this, I admit quite different, context it just won't work. Let me post the original solution:

ItemizedProductLine::ItemizedProductLine(ProductCode pc, double rrp, double sp, int oh, char* desc): ProductLine(pc, rrp, sp, oh, desc){
    
    string serial;

    // obtain user input to obtain serial numbers. Pressing enter (blank) quits       

    cout << "Please enter a serial number. Enter to quit: ";
    
    getline(cin, serial);

    while(!serial.empty())
    {
        serialNumbers.insert(serial);
        
        cout << "Please enter a serial number. Enter to quit: ";
        
        getline(cin, serial);
    }
}

Ok, so this works swimmingly! It makes sense to me. I should correctly attribute this code to NathanOliver (http://www.daniweb.com/forumsthread286345.html?utm_source=vBMail&utm_medium=email&utm_campaign=ThreadbitDigest). Thanks, Nathan. However, when I try to call the following function, it acts as if I have pressed enter (when blank) and returns to the calling function. I think I should add that this function is a virtual one. I am not sure if that is material. Here is the code for the offending article:

void ItemizedProductLine::Sold(int qty){
    
    // if the requested quantity is greater than available - no sale.
    if(qty > onHand)
    {
        cout << "Only " << onHand << " available - Sale cancelled" << endl;
    }
    //otherwise all good. Reduce onHand by one and increase the number sold today by //one.
    else
    {
        cout << "Total Price: " << qty * salePrice << endl;

        onHand -= qty;

        soldToday += qty;
    }

    string serial;

    cout << "Enter serial number to be removed. Enter to quit:";

    getline(cin, serial);

    while(!serial.empty())
    {
        // remove the number from the set
        serialNumbers.erase(serial);

        cout << "Please enter serial number to be removed. Enter to quit: ";

        getline(cin, serial);
    }
}

Let me explain my reasoning, and we'll see if that is the first port-of-call as regards the problem!
1 - I arrive at the output point of the function. Message is printed to screen.
2 - I request a line of input, as per the first function. Crash! Bang!
3 - If we are getting to the while condition, the string is empty I guess. From here on, I don't really know what is going on.

Point 2, I think is where things are going wrong. My other thought was that I have to clear the input or some such, as I do use getline earlier in the program.

Guys, any help would be greatly appreciated - as ever! Thanks in advance.

Daniel

[Radical Edward]

> 2 - I request a line of input, as per the first function. Crash! Bang!
Why you say crash, do you mean the program crashes? Can you walk Ed through each step with the input and output? Or better yet, post a short program that Edward can run to reproduce the problem. :)

[NathanOliver]

You could have a newline in the input buffer that is getting extracted by the call to getline. That would give you an empty string. Try doing this.

//...
cin.ignore(80, '\n');
cout << "Enter serial number to be removed. Enter to quit:";
getline(cin, serial);

[daniel88]

Nathan, you come to the rescue again! Thanks, mate. That's it. As I suspected it was going to be something straightforward. I really appreciate your help.

Daniel