Thread: understanding getchar(), buffered user input, and so on...

First... post your code here. Don't make us go chasing it... 'cause we won't.

Buffered input means that every keystroke... even ones that don't get processed, are stored in an input buffer. At some point you need to clear it out.

For example, when you have..

Code:

int c;
printf("Enter a letter : ");
c = getchar();

so the prompt comes up and you press in A then you hit the <enter> key... BOTH keystrokes go into the buffer, the A is read back by the getchar() leaving the <enter> key behind... Now you need to clear that out before calling your next input function, or it will simply see you pressing <enter>.

Worse still you could enter "My name is fred and I like to eat spam" and hit enter... The only thing that is assigned is the M, leaving the rest behind.

The usual method is to loop until you find the newline...

Code:

while(getchar() != '\n');

... is usually adequate to ensure an empty input buffer for your next user input.

Originally Posted by CommonTater

First... post your code here. Don't make us go chasing it... 'cause we won't.

All right. I thought the codes were "too long" (70 and 80 lines) to be pasted here, and I didn't want to place just part of them, since I didn't have a clue on where the problem was. I will not repeat that.

Originally Posted by CommonTater

Buffered input means that every keystroke... even ones that don't get processed, are stored in an input buffer. At some point you need to clear it out.

For example, when you have..

Code:

int c;
printf("Enter a letter : ");
c = getchar();

so the prompt comes up and you press in A then you hit the <enter> key... BOTH keystrokes go into the buffer, the A is read back by the getchar() leaving the <enter> key behind... Now you need to clear that out before calling your next input function, or it will simply see you pressing <enter>.

Worse still you could enter "My name is fred and I like to eat spam" and hit enter... The only thing that is assigned is the M, leaving the rest behind.

I think you explained the issue clearly and accurately. I made some tests and they indeed returned what I expected based on what I learned from you.

Originally Posted by CommonTater

The usual method is to loop until you find the newline...

Code:

while(getchar() != '\n');

... is usually adequate to ensure an empty input buffer for your next user input.

Thanks for the tip. I'll try to use it more often.

Good explanation indeed. And i'd be the first to lurk around threads containing the titles "buffered".

On the topic, what is the buffer size defined by the library used for getchar()? And according to your while statement, are you not merely reaching the end of the buffer, you're not really clearing it? In that case memory will somehow lurk throughout the life of the programme execution?