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

copy paste:

Code:

bool ErrorDisplay = false;
	int Input;
	do
	{
		if (ErrorDisplay) wcout << 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
		wcin.clear();//reset errorflags
		wcin.ignore(wcin.rdbuf()->in_avail()); //ignore everything that's in the buffer
		wcout << AskText << L": "; //ask the user for the input (textwise)

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

it seems

Code:

wcin.rdbuf()->in_avail()

always returns 0, while it should be returning the number of characters in the buffer that are ready to be read.

I have constructed something else in the mean time, which does the same but works:

Code:

int ServerEngine::GetCinIntInput(const tstring& AskText, const tstring& ErrorText) const
{
	bool ErrorDisplay = false;
	int Input;
	tstringstream tmp;
	do
	{
		if (ErrorDisplay) tcout << 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
		tcout << AskText << _T(": "); //ask the user for the input (textwise)
		TCHAR buf[1024];
		tcin.getline(buf,1024);
		tmp.clear();
		tmp.str(_T(""));
		tmp << buf;

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

This is using some defines to switch between mbcs and unicode based on project settings.

However if somebody finds out why that other method didn't work, I'm always happy to hear it and learn something new.

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;
}

that's working perfectly as it should too, thanks.

Still wondering why the wide version rdbuf/in_avail behaves so differently, it may be a mystery forever

Which STL are you using?

gg

Originally Posted by Codeplug

Which STL are you using?

gg

Not sure if I know what you mean, but I'm using the headers supplied by Visual Studio 2005.