Clear the cin buffer before another input request, c++

Question

I have the following code:

int choice = 0;
char st1[N];

cout << "enter choice" <<endl;
cin >> choice;

cout << "enter sentence" << endl;
cin.get(st1, N-1);

when getting to cin.get line, no matter what the input is, it will read \0 char into st1[0] and that's it.

I assume it has something to do with the latest cin ( into choice variable ).

How do i "clean" cin buffer before getting new input from the user? if that's possible.

thanks

I advise using getline(cin, aString); This will never leave any input behind in the stream + it's type safe. — user3152069, May 17 '14 at 16:00

score 3 · Accepted Answer · edited May 23 '17 at 11:50

3

You might use ignore to drop the newline from the buffer (e.g. drop X characters before the newline as delimiter). Extraction and ignore stop when the delimiter is extracted.

e.g.

cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');

Also related: Why would we call cin.clear() and cin.ignore() after reading input?

edited May 23 '17 at 11:50

Community

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answered May 17 '14 at 15:59

Marco A.

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What happens, if the input was s.th. like this: `3 \n`? – πάντα ῥεῖ May 17 '14 at 16:22
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THX for the sample, I already upvoted your answer. I just wanted to put this in contrast to the other _"answer"_ ... – πάντα ῥεῖ May 17 '14 at 16:31

score 0 · Answer 2 · answered May 17 '14 at 16:41

0

You could always try using cin.sync().

answered May 17 '14 at 16:41

Callum

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score -1 · Answer 3 · answered May 17 '14 at 15:58

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Do a getchar() after cin >> choice;. This will consume the \n from the input buffer.

Since choice is of type int, the \n is left over in the buffer and when the string input is taken, this \n is encountered and it stops taking input there.

answered May 17 '14 at 15:58

HelloWorld123456789

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This doesn't really _clear_ the `cin` input buffer. As a last resort `cin.clear()` will do, including resetting all the stream error states. – πάντα ῥεῖ May 17 '14 at 16:10
This will not clear the input buffer, but will get the job done in OP's case. – HelloWorld123456789 May 17 '14 at 16:12
There's no guarantee that a single `getchar()` call will do the job correctly. That completely depends on, what the user actually enters at `cin >> choice;`! – πάντα ῥεῖ May 17 '14 at 16:16
In that case other solutions may fail to work too. It's a different case altogether. – HelloWorld123456789 May 17 '14 at 16:27

Clear the cin buffer before another input request, c++

3 Answers3

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