Is there a function to retrieve integer input?

Question

This one is kinda specific. I want to be able to retrieve an integer from the user using a function rather than cin. I have tried several different things, but none seem to work so I have just wound up writing my own function. It really does baffle me though because it seems like something that would have a function in existence already. Here it is:

int getInt()
{
   int num;
   cin >> num;
   return num;
}

I have tried using cin.get(), but that returns the ascii number for the integer. The getline() functions are all for strings. It just doesn't make sense that this function doesn't exist! If you know of any function or in-line equivalent that could be passed as a parameter to a function, let me know.

Why do you think this function should exist? It's easy enough to write your own. Note that your function is extremely specific, and the functionality to write it is readily available. How big do you think the C++ standard library should be? — David Thornley
– David Thornley, Commented Jan 5, 2011 at 17:44
Are you doing this so you can declare and initialize in one line? int x = getInt(); — Loki Astari
– Loki Astari, Commented Jan 5, 2011 at 17:54
This function is missing major functionality: namely it returns an undefined value if the read fails for any reason. This is a bad thing. — Mooing Duck
– Mooing Duck, Commented May 13, 2015 at 0:10

AProgrammer · Accepted Answer · 2011-01-05 17:27:13Z

2

There is no standard function doing what you want.

answered Jan 5, 2011 at 17:27

AProgrammer

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Comments

Steve Townsend · Accepted Answer · 2011-01-05 17:30:31Z

2

You are already using a function when you do what you posted. Alternative syntax for the call to operator>> that makes this clearer:

   int num;
   cin.operator>>(num);
   return num;

Here's the code for that function from the Visual C++ v10 header:

_Myt& __CLR_OR_THIS_CALL operator>>(int& _Val)
    {   // extract an int
    ios_base::iostate _State = ios_base::goodbit;
    const sentry _Ok(*this);

    if (_Ok)
        {   // state okay, use facet to extract
        long _Tmp = 0;
        const _Nget& _Nget_fac = _USE(ios_base::getloc(), _Nget);

        _TRY_IO_BEGIN
        _Nget_fac.get(_Iter(_Myios::rdbuf()), _Iter(0),
            *this, _State, _Tmp);
        _CATCH_IO_END

        if (_State & ios_base::failbit
            || _Tmp < INT_MIN || INT_MAX < _Tmp)
            _State |= ios_base::failbit;
        else
            _Val = _Tmp;
        }

    _Myios::setstate(_State);
    return (*this);
    }

answered Jan 5, 2011 at 17:30

Steve Townsend

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6 Comments

Cory-G Over a year ago

Well, what I am actually looking for is an existing function that does what mine above does as a whole. That way you can pass it as a parameter like so:

Cory-G Over a year ago

for(int num = getInt(); num != 42; num++)

Steve Townsend Over a year ago

That loop does not make sense to me - do you want something like: while (cin.operator>>(num) && num != 42) ?

user395760 Over a year ago

And @Steve's code can be even simpler, while (cin >> num && num != 42)!

Cory-G Over a year ago

Doesn't that call it every time? I just want it to be called once at the beginning and then at the end of every loop. I could just put it before the loop, but I was hoping to keep the variable only in the scope I was using it in (I am an avid enemy of the spammed variables.) To see the exact context I am talking about check out the easy challenge on Code Chef called 'Life, the Universe, and Everything.' My code for the loop ends up as: for(int num = getInt(); num != 42; cin >> num) cout << num << endl;

|

Shamim Hafiz - MSFT · Accepted Answer · 2011-01-05 17:27:11Z

0

C++ uses operators(in this case >>) to take input unlike Java which uses functions. You can build your own number parser, but there isn't one built in with standard C++.

answered Jan 5, 2011 at 17:27

Shamim Hafiz - MSFT

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