Input validation loop failure

This is a discussion on Input validation loop failure within the C++ Programming forums, part of the General Programming Boards category; Code: double readDouble( void ) { double input; while (!(cin >> input)) { cout << "Invalid data.\n"; cin.clear(); cin.ignore(numeric_limits< double ...

  1. #1
    Registered User MacNilly's Avatar
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    Input validation loop failure

    Code:
    double readDouble( void )
    {
        double input;
    
        while (!(cin >> input))
        {
            cout << "Invalid data.\n";
            cin.clear();
            cin.ignore(numeric_limits< double >::max(), '\n');
        }
        return input;
    }
    I get this warning when compiling on Dev-C++ 4.9.9.2

    Code:
    68 C:\Projects\CISP400\invdata.cpp [Warning] passing `double' for converting 1 of `std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::ignore(std::streamsize, typename _Traits::int_type) [with _CharT = char, _Traits = std::char_traits<char>]'
    Problem is that if I enter a character or any invalid data it goes into the infinite loop that I am trying to avoid. I have the same loop in a function for integers but no problems there.

  2. #2
    Registered User
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    Look at the defintion of cin.ignore() and the types of its parameters. Then, look at the types you are passing it. In C++, the types of the arguments you send to a function have to match the types of the parameters in the function definition.

  3. #3
    Registered User MacNilly's Avatar
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    Ok, it takes an integer. I tried static_cast 'ing the whole expression to an int but still get infinite loop. Is there any way to do what I'm trying here?

  4. #4
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    Try:

    cin.ignore(numeric_limits<streamsize >::max(), '\n');

  5. #5
    Registered User MacNilly's Avatar
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    Ah, very nice. Much appreciated.

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