Input Chunking: How to

[shotgunmoose]

Hello All!

I was wondering if anyone knows of a way that is similar to JAVA's system.in.skip(#); command in C, or if there isn't, is there a way to get around unwanted char inputs by the user in a scanf("%c",&option) line?

thanks for your time and help.

[Deckard]

Hi Moose,

I'm not familiar with Java (ask Iain how lucky that makes me). Would you give an example of what you mean by "unwanted char inputs"? If you want to remove certain characters from a string, I would iterate through it. If you want to see if the value in a single character is valid, just test the value.

I suspect I'm not fully understanding your question :)

Thanks.

[quzah]

There are ways to scan and ignore:

%d == read a number
%*d == read, but ignore a number

The same applies for other values. Additionally, you can use:

%[abc] == read these values only
%[^abc] == read anything but these

Or, you can just scan input a character at a time.

Quzah.

[shotgunmoose]

Well, I'm currently not getting the response I'd like, so here's an example of what I'm trying to do...

i.e.

"Please Enter a Character:"
(User enters-->)abc

"You Entered: a"

(I'm trying to get rid of all the excess garbage that the user enters, including the '\n'(return line) character. But still keeping the 'a'.

I've tried the following: ("%c%c",&option).. but that doesn't seem to help really.. just screws up later by not allowing ANY other character to be inputted.. as it assumes its an invalid character... blah blah balh ..(its the way my code's set up).

[QuestionC]

There's a couple ways to do this...

First, you can make a FLUSH macro to flush the input buffer...

#define FLUSH for (;getchar() != '\n';)

// ... Somewhere in the file, we want to get input...
printf ("Gimme Input.\n");
scanf ("%c", &myChar);
FLUSH;
// Now myChar has the first letter, and everything else that was
//  in the buffer has been trashed by FLUSH

Second, you can just grab the string with gets() and process that string...

char tempInput[80];
printf ("Gimme Input.\n");
gets (tempInput);
sscanf (tempInput, "%c", &myChar);

Incidentally, even though gets will generally work, provided your array is large, it is much safer to use fgets().

Finally, there's the conversion specifiers. I'm not too sure about this one, but I think this will do the trick...

printf (Gimme Input.\n");
scanf ("%c%*[^'\n']%*c", &myChar);

That format string basically says this....
%c get a character
%*[^'\n'] get the longest string possible that does not contain the character '\n'. The * specifies that we don't want to store this string.
%*c get the next character (which is obviously the '\n'). The * specifies that we don't want to store thsi character.

I haven't tested any of these code segments, but I'm pretty sure they're working. I suggest choosing whatever method makes the most sense to you.

[Garfield]

Look, I pretty sure that scanf doesn't scan in the '\n' char. You won't have to worry about that. It scans only what you specified into the specified vars (if string -- null terminated). fgets is the one that you have to do something like:

fgets(line, sizeof(line), stdin);
line[strlen(line)-1] = '\0';

To alter the '\n' to an early '\0'.

[Salem]

> line[strlen(line)-1] = '\0';
If the user filled the buffer, there will be no \n to remove, and this instead overwrites the last char of user input.

See several of my previous posts which use strchr

[Garfield]

Originally posted by Salem
> line[strlen(line)-1] = '\0';
If the user filled the buffer, there will be no \n to remove, and this instead overwrites the last char of user input.

See several of my previous posts which use strchr

Well, if you make a "comfortable" buffer (something like line[512] as the char array), you shouldn't have to worry about something like that. Taking the extra steps isn't worth it in this case and will only defeat the optimization purpose (not that that is what he/she is aiming at, but that should always be in the back of your mind).

[Salem]

> Well, if you make a "comfortable" buffer (something like line[512] as the char array),
So it's OK to use gets with a comfortably large buffer is it?

All you're doing is moving the probability of a problem closer to 0 - that is all.

> Taking the extra steps isn't worth it in this case and will only defeat the optimization purpose
And what do you imagine is the difference between
strlen( buff ) and strchr( buff, '\0' );

A highly optimised bug is still a bug.

[Garfield]

Originally posted by Salem
A highly optimised bug is still a bug.

You're right, Salem. That is the best method to do it. Better off to be safe with looking towards the last char.