invalid argument exception

[deb9]

Hi,

I have a method to read input from a user like this

int cmd = 0;
while (true) {
try {
cout << "Menu of options: 1) New game 2) Mark 3) Status 4) Exit";
cin >> cmd;
}
catch (?????) {
cout<<"Invalid input. Try again"<<endl;
continue;
}
}

I am using a try and catch block in case the user types a string or a non-numeric character. In that case I would like in the catch to just print the message and ask again.
What are the arguments to the catch? Do I need to include any exception library?

Thanks

Debbie

 

[uolj]

There is no exception thrown on invalid input, so the try/catch block is useless in this case.

To check for valid input, you check the return value of operator>>. If it is false, the input failed, and you need to clear the input stream fail state (and probably ignore the characters in the stream). Here is one way of doing this:

while (true) {
  cout << "Menu of options: 1) New game 2) Mark 3) Status 4) Exit";
  if (!(cin >> cmd)) {
    cout<<"Invalid input. Try again"<<endl;
    cin.clear();
    cin.ignore(numeric_limits<streamsize>::max(), '\n');
    continue;
  }
  // ...
}

You must #include <limits> to use the numeric_limits there, or you can just replace that part with a large number like 100 or 1000 so that at most that many bad characters input by the user will be ignored.

 

[cpjust]

I don't see any way that an exception can be thrown with that code. Here is the proper way to do what you want:

	int cmd = 0;
    while ( true )
	{
		cout << "Menu of options: 1) New game 2) Mark 3) Status 4) Exit";
		cin >> cmd;

		// Do something with cmd here...

		if ( !cin )			// If stream state is bad.
		{
			cin.clear();	// Set stream state back to good.
			cin.ignore();	// Ignore the bad input.
		}
		else if ( (cmd >= 1) && (cmd <= 4) )
		{
			continue;
		}

		cout << "Invalid input. Try again" << endl;
	}

 

[cpjust]

Oops, I put the "// Do something..." in the wrong place.

    int cmd = 0;
    while ( true )
    {
        cout << "Menu of options: 1) New game 2) Mark 3) Status 4) Exit";
		
        if ( !(cin >> cmd) )	// If stream state is bad.
        {
            cin.clear();		// Set stream state back to good.
            cin.ignore();		// Ignore the bad input.
			cout << "Invalid input. Try again" << endl;
			continue;
		}
        else if ( (cmd < 1) || (cmd > 4) )
        {
			cout << "Invalid input. Try again" << endl;
			continue;
        }
		
        // Do something with cmd here...
    }