getline() and cin.ignore()

swappo · 06-27-2009, 11:29 AM

I have a program where I call getline(cin, something); multiple times. I need to clear the input buffer of '\n' but if I use cin.ignore() after getline(), I get a cursor on the command line and have to hit enter before being prompted for the next input. How do I clear the input buffer with out this extra line?

**laserlight** · 06-27-2009, 11:31 AM

Quote:

Originally Posted by swappo

I have a program where I call getline(cin, something); multiple times. I need to clear the input buffer of '\n'

The newline is also consumed by the getline call, so you do not need to get rid of it.

swappo · 06-27-2009, 11:42 AM

Example:

Code:

char loop = 'y';
	while(loop != 'n')
	{
		cout << "Enter a name: ";
		getline(cin, name);
		cout << "Enter a number: ";
		getline(cin, num);
		numbers[name] = num;
		cout << "Enter another name and number? 'y' or 'n': ";
		cin >> loop;
	}

Here is my output without flushing the buffer:

Code:

Enter a name: me
Enter a number: 45
Enter another name and number? 'y' or 'n': y
Enter a name: Enter a number:

How would I fix this?

**laserlight** · 06-27-2009, 11:44 AM

You would use cin.ignore() after this line to ignore as many characters as necessary until the newline character:

Code:

cin >> loop;

swappo · 06-27-2009, 11:53 AM

If I put cin.ignore() after getline(cin, name); I have a line with just a cursor which I have to hit enter to get to the next line of input. Yet, I put cin.ignore() after cin >> loop; as you suggested it works without that extra line. I don't understand why I get differing results with the different placements of cin.ignore().

**laserlight** · 06-27-2009, 11:58 AM

Quote:

Originally Posted by swappo

If I put cin.ignore() after getline(cin, name); I have a line with just a cursor which I have to hit enter to get to the next line of input. Yet, I put cin.ignore() after cin >> loop; as you suggested it works without that extra line. I don't understand why I get differing results with the different placements of cin.ignore().

As I noted, getline would consume the newline. Thus, if there is no newline to ignore, you end up waiting for more input, against your intention. On the other hand, formatted input with operator>> does not consume the newline (by default, if I remember correctly), thus there is (at least) a newline left in the input buffer. If this newline is not ignored, the next call to getline will consume it, against your intention.

swappo · 06-27-2009, 12:12 PM

Ok, thanks.

06-27-2009, 11:29 AM	#1
swappo Registered User Join Date: Nov 2008 Posts: 56	getline() and cin.ignore() I have a program where I call getline(cin, something); multiple times. I need to clear the input buffer of '\n' but if I use cin.ignore() after getline(), I get a cursor on the command line and have to hit enter before being prompted for the next input. How do I clear the input buffer with out this extra line?
swappo is offline

06-27-2009, 11:44 AM	#4
laserlight C++ Witch Join Date: Oct 2003 Location: Singapore Posts: 10,352	You would use cin.ignore() after this line to ignore as many characters as necessary until the newline character: Code: cin >> loop; __________________ C + C++ Compiler: MinGW port of GCC Build + Version Control System: SCons + Bazaar Look up a C/C++ Reference and learn How To Ask Questions The Smart Way
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06-27-2009, 11:53 AM	#5
swappo Registered User Join Date: Nov 2008 Posts: 56	If I put cin.ignore() after getline(cin, name); I have a line with just a cursor which I have to hit enter to get to the next line of input. Yet, I put cin.ignore() after cin >> loop; as you suggested it works without that extra line. I don't understand why I get differing results with the different placements of cin.ignore().
swappo is offline

06-27-2009, 12:12 PM	#7
swappo Registered User Join Date: Nov 2008 Posts: 56	Ok, thanks.
swappo is offline

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