Thread: clearing wcin buffer

I have a function which asks for a number and keeps reasking until a real number is given, and then returns that number. It works perfectly with cin, but it doesn't when I convert everything to the wide version.

Working version:

Code:

int GetCinIntInput(const string& AskText, const string& ErrorText) const
{
	bool ErrorDisplay = false;
	int Input;
	do
	{
		if (ErrorDisplay) cout << ErrorText << endl; //if error should be displayed display it
		ErrorDisplay = true; //first time in the loop it's not an error, but from this point it will always be an error until the loop ends
		cin.clear();//reset errorflags
		cin.ignore(cin.rdbuf()->in_avail()); //ignore everything that's in the buffer
		cout << AskText << ": "; //ask the user for the input (textwise)

	}while(!(cin >> Input)); //await input and look if it goes into the integer, if it does, the loop exits and mission accomplished
	return Input;
}

Not working version: cin becomes wcin, cout becomes wcout and string becomes wstring.
It compiles but it just turns into an infinite loop of the error msg (if input is a text, it works if the input is a number).

Let's see the code that doesn't work. Forgetting to change "cin.clear()" to "wcin" would do that.

gg

I would write:

Code:

wcin.ignore(numeric_limits<streamsize>::max());

Originally Posted by laserlight

I would write:

Code:

wcin.ignore(numeric_limits<streamsize>::max());

It seems to be if you give a number of characters to ignore which is larger than the amount that is in, it will wait before continueing the code until the buffer has reached that size, if I were to pass on 10 for example, in runtime I would have to type "lol" 3 times each followed by a enter before it notifies me that an error took place because I didn't enter a valid number. And if I pass to few, e.g. 1, and I type "lol" followed by enter, it'll say the error msg 3 times.
I haven't studied it more, but that's what my testruns showed me.
I have also tried using an additional delimiter as second param: '\n' but on the very first execution it completely ignores the first input.

Originally Posted by s-men

It seems to be if you give a number of characters to ignore which is larger than the amount that is in, it will wait before continueing the code until the buffer has reached that size

Oh yes, I forgot that the default second argument is EOF, not '\n'.

Originally Posted by s-men

I have also tried using an additional delimiter as second param: '\n' but on the very first execution it completely ignores the first input.

A more canonical implementation would be:

Code:

int ServerEngine::GetCinIntInput(const tstring& AskText, const tstring& ErrorText) const
{
    int Input;
    for (;;)
    {
        tcout << AskText << _T(": "); //ask the user for the input (textwise)
        if (wcin >> Input)
        {
            break;
        }
        else
        {
            tcout << ErrorText << endl;
            wcin.clear();
            wcin.ignore(numeric_limits<streamsize>::max(), '\n');
        }
    }
    return Input;
}

Which STL are you using?

gg