Is there anyway in c++ that I can use an "if" to see if a variable is a of a specific type?

Question

Ok so the basic idea is that I want to use an if so i can output an message that tells the user that the type he just inputted is a wrong type I did something like this:

int n;

cout<<"how many names do you want to register"<<endl;

cin>>n;

if (n != int) {

cout<<"Please input an integer value"

}

I understand that I will have to put some sort of loop but I hope this gets the idea out, I want to do this because I see a lot of people making mistakes with the type..

please help and thanks!

? · Accepted Answer

Yes there is a way to use an "if" to see if an object has a specific type, but in your case the type of n is int (you've defined it that way!), and such test will always be true.

If the user attempts to input something that is not an int, the line "cin >> n;" will not write anything into n; it will set the stream error flags instead. That's what you have to test with your if:

int n;

cout<<"how many names do you want to register"<<endl;

cin>>n;

if (!cin) {

cin.clear(); // unset the error flag

cin.ignore( numeric_limits<streamsize>::max(), '\n'); // get rid of the bad input

cout<<"Please input an integer value";

}

test: https://ideone.com/56hIU

green meklar · Answer

Input into a char array, then parse the char array to check whether it's a valid integer, and convert it using atoi() if it is valid.

Note that completely safe input to a char array is actually surprisingly difficult. However, if you operate under the assumption that inputs will not exceed a certain relatively small length, it makes it much simpler.

Trending News

Is there anyway in c++ that I can use an "if" to see if a variable is a of a specific type?

2 Answers