Thread: flushing ....

Why is it that flushall(); works for me in this code and cout.flush(); doesn't??

Code:

while ( i<drivers )
{
	cout.flush();	//not working like flushall();

//	flushall();		//was used, but it don't really want
			//to need to have it there if possible

	cout<< endl << "What is your name: ";
	cin.getline( TempName, NAME_SIZE );	

//	to be entered into a struct, but I didn't put it in this
//	cause it would just clutter up the post 

}

basically, when I have flushall(); it works fine in that the program doesn't skip the getting name thing. but if I put cout.flush(); it doesn't work and if I don't have any flushing thing there it acts as it would with cout.flush() or rather cout.flush acts as if there wasn't any flusher.

I bet that if someone compiles this they actually won't need a buffer for it which leads me to further confusion ... argh

In your example code I don't see any need to flush cout

Code:

while ( i<drivers )
{
	cout<< endl << "What is your name: ";  // endl will flush cout
	cin.getline( TempName, NAME_SIZE );	// cin / cout are synchronized so getline flushes cout

}

Kurt

you may also want to add:

Code:

std::cin.getline(TempName,NAME_SIZE,'\n');

just so that it stops when you hit enter (the way you have it, it'll keep taking input until the array is full)

cin.getline(TempName, NAME_SIZE)

is eqivalent to:

cin.getline(TempName, NAME_SIZE, '\n')

thanks for your reply Zuk/Kurt and major_small !!

Originally Posted by ZuK

In your example code I don't see any need to flush cout

I didn't see any reason to have to flush either, but when I compiled the code it skipped the "Enter your name" thing and went straight to the second thing without inputting anything ...

Originally Posted by major_small

you may also want to add:
Code:
std::cin.getline(TempName,NAME_SIZE,'\n');

that sir, is highly aloof! I had it in the code, but it didn't copy ... must have been a backup file that I copied it from, one which didn't have the '\n' terminator or something similar.

Originally Posted by major_small

did you try:
Code:
std::cout<<std::flush();

I just tried that, with the correction that you posted, and it still didn't do anything to help with the flushing ... does anyone know what the cause of that may be?? Could it have anything to do with the code preceeding it?? if so, all that's being done before is creating a dynamically allocated array and testing to see if it was created correctly .... i'm big time confused!

>> Could it have anything to do with the code preceeding it??
Normally it has. But it has nothing to do with cout.
if you use some statement like

Code:

cin >> number;

before using getline() it will retun an empty string because there would still be a '\n' left in the buffer.
It's never a good idea to mix different types of input statements.
But that is all in the FAQ's
Kurt

One easy solution to the issues from mixing cin >> and getline is to add cin.ignore() after any call to cin >>, and specifically after any call to cin>> that comes before a call to getline.

Originally Posted by Daved

One easy solution to the issues from mixing cin >> and getline is to add cin.ignore() after any call to cin >>, and specifically after any call to cin>> that comes before a call to getline.

good call Daved!! works like a treat now! thanks a bunch! I'm still kinda confused about why I had to do it, cause i don't really think I needed to do it before in similar things ...

As ZuK said, operator>> leaves a newline in the buffer. For example, if you prompt the user for a number and they type 3 and then hit enter, then cin >> number will read the 3 into the variable and stop. However, there will be a newline from when the user hit enter that is still in the stream. Later, you call getline, which just reads until it reaches it's delimiter (which is a newline by default). So if there is a newline in the stream from the previous cin >> call, then that newline is picked up by the getline call and nothing else is read in. The cin.ignore() works by ignoring the newline left in the input stream.

The reason the ignore() isn't necessary when you have a second call to cin >> after the first one is that operator>> ignores leading whitespace (including newlines). So the newline that is in the input buffer from the first call to cin >> is ignored automatically and the second call to cin >> just waits for the user to type in more stuff.