How do I flush the cin buffer?

Question

How do I clear the cin buffer in C++?

Answer 1

I would prefer the C++ size constraints over the C versions:

// Ignore to the end of file
cin.ignore(std::numeric_limits<std::streamsize>::max())

// Ignore to the end of line
cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n')

Answer 2

Possibly:

std::cin.ignore(INT_MAX);

This would read in and ignore everything until EOF. (you can also supply a second argument which is the character to read until (ex: '\n' to ignore a single line).

Also: You probably want to do a: std::cin.clear(); before this too to reset the stream state.

Answer 3

cin.clear();
fflush(stdin);

This was the only thing that worked for me when reading from console. In every other case it would either read indefinitely due to lack of \n, or something would remain in the buffer.

EDIT: I found out that the previous solution made things worse. THIS one however, works:

cin.getline(temp, STRLEN);
if (cin.fail()) {
    cin.clear();
    cin.ignore(numeric_limits<streamsize>::max(), '\n');
}

Answer 4

I have found two solutions to this.

The first, and simplest, is to use std::getline() for example:

std::getline(std::cin, yourString);

... that will discard the input stream when it gets to a new-line. Read more about this function here.

Another option that directly discards the stream is this...

#include <limits>
// Possibly some other code here
cin.clear();
cin.ignore(numeric_limits<streamsize>::max(), '\n');

Good luck!

Answer 5

int i;
  cout << "Please enter an integer value: ";

  // cin >> i; leaves '\n' among possible other junk in the buffer. 
  // '\n' also happens to be the default delim character for getline() below.
  cin >> i; 
  if (cin.fail()) 
  {
    cout << "\ncin failed - substituting: i=1;\n\n";
    i = 1;
  }
  cin.clear(); cin.ignore(INT_MAX,'\n'); 

  cout << "The value you entered is: " << i << " and its double is " << i*2 << ".\n\n";

  string myString;
  cout << "What's your full name? (spaces inclded) \n";
  getline (cin, myString);
  cout << "\nHello '" << myString << "'.\n\n\n";

Answer 6

How about:

cin.ignore(cin.rdbuf()->in_avail());

Answer 7

I prefer:

cin.clear();
fflush(stdin);

There's an example where cin.ignore just doesn't cut it, but I can't think of it at the moment. It was a while ago when I needed to use it (with Mingw).

However, fflush(stdin) is undefined behavior according to the standard. fflush() is only meant for output streams. fflush(stdin) only seems to work as expected on Windows (with GCC and MS compilers at least) as an extension to the C standard.

So, if you use it, your code isn't going to be portable.

See Using fflush(stdin).

Also, see http://ubuntuforums.org/showpost.php?s=9129c7bd6e5c8fd67eb332126b59b54c&p=452568&postcount=1 for an alternative.

Answer 8

Another possible (manual) solution is

cin.clear();
while (cin.get() != '\n') 
{
    continue;
}

I cannot use fflush or cin.flush() with CLion so this came handy.

Answer 9

Easiest way:

cin.seekg(0,ios::end);
cin.clear();

It just positions the cin pointer at the end of the stdin stream and cin.clear() clears all error flags such as the EOF flag.

Answer 10

The following should work:

cin.flush();

On some systems it's not available and then you can use:

cin.ignore(INT_MAX);

Answer 11

#include <stdio_ext.h>

and then use function

__fpurge(stdin)

Answer 12

It worked for me. I have used for loop with getline().

cin.ignore()

Answer 13

cin.get() seems to flush it automatically oddly enough (probably not preferred though, since this is confusing and probably temperamental).