Re: Keyboard input (newbie question)

 James Kanze <>
Fri, 09 Nov 2007 09:22:15 -0000
On Nov 8, 6:56 pm, Tarique <> wrote:

How can i clear the input buffer before i accept a user input?

You can't, at least not in standard C++. You'll have to use
something specific to your implementation.

Further what is the correct way to clear the buffer in case of
an *invalid* input.

Read ahead, ignoring input, until the next synchronization
point. If the next synchronization point is a new line (a
frequent case), then std::cin.ignore() can be used. Just don't
forget to clear the error first.

If the input is line oriented (and thus, new lines aren't just
"white space") the usual idiom is to read it line by line, using
getline, and then use an istringstream to extract the data from
the line.

The following naive program will show up the error. any help
will be greatly appreciated.

using namespace std;

class Publication
        char title[30];
        float price;

        void getdata(void)
                cout<<"Title :"<<endl;

Don't ever do this!!! There is NO correct use of gets. (Also,
mixing FILE* input and istream isn't generally a good idea,

If you want to read a complete line, use getline().


If you're inputing by line (which would seem to be the case),
something like:

    std::string line ;
    std::cin >> line ;
    std::istringstream s( line ) ;
    s >> price >> std::ws ;
    if ( ! s || s.get() != EOF ) {
        // error...

is preferable. (Of course, you should also check for an error
after reading the line.) It reads a complete line, leaving the
stream is a good state if there is a line, regardless of what it
contains. It then converts the double, eats any trailing white
space, and checks for errors...including extra garbage at the
end of the line. And error or not, you're automatically
synchronized for the next line.

James Kanze (GABI Software)
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