C++: an input validator function

Question

I have written the following function:

void check(int* input){

do{
    std::cout<<"Enter integer!";
    std::cin>>*input;
}while(!std::cin);
}

And I am using it in the main function as follows:

int main()
{
    int *k;
    k=new int;
    check(k);
    std::cout<<"Value of the k is:"<<*k<<"in address"<<k;
    return 0;
}

The problem is when user input some characters, the compiler keep printing "Enter integer!", non-stop, and I have to stop the compiler manually.

Unrelated to your problem, but why do you allocate the integer dynamically in main? Why use pointers at all? Why not simple references? — Some programmer dude
– Some programmer dude, Commented Mar 23, 2018 at 7:08
As for your problem, it's well-known problem with plenty of duplicates here. It stems from the input not being removed from the buffer. You need to clear or ignore the existing input. — Some programmer dude
– Some programmer dude, Commented Mar 23, 2018 at 7:10

Hawkeye5450 · Accepted Answer · 2018-03-23 07:16:45Z

1

What is happening is the stream is breaking. Basically, the program sees a character going into something that isn't a character and freaks out, which is UB. It is a simple fix you can find in just about any beginning level books that include data validation:

#include <limits>

if(cin.fail())
{
    cin.clear();
    cin.ignore(numeric_limits<streamsize>::max(), '\n');
}

This tests if the stream is broken, clear the flag and ignore the rest of the input on the line.

answered Mar 23, 2018 at 7:16

Hawkeye5450

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