Thread: fgets, sscanf question.....

The code below is kinda hard to read, it's a portion of a program I'm trying to make for ANSI DOS. I used fgets and sscanf (only learned about sscanf yesterday - but I see already it rocks), and the program works perfect so far. But I'm curious as to why, when I first tried it, I delcared a char buf[2], figuring that meant that buf[2] = '/0'. Then I had origionally had it where (fgets(buf,1,stdin); - however, when I did, when that part of the program loaded, it would immediatly say "You did not enter a number" - I mean as soon as it came up on the screen, you never had a chance to type anything. Changing it to 2 works just fine, and I know in most examples it's char buf[256], but in this case I'm only receiving one letter, for a menu selection, so I really don't need an array that large. Like I said, it's fixed, I just changed it to 2, and now it works great, but I'd like to know why when you just have fgets read in 1 instead of 2 it does that.

Thanks again,

ash

Code:

void intro() {

	cls();

	printf("\x1b[31m");

	printf("\n\n\n\n\n\n\n\n\n\n\n\n\n");
printf("                     Welcome to Smith Sayings - Freeware Edition\n");
	printf("\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n");
	printf("\x1b[34m");
	printf("                            Press <ENTER> to continue...\n");

	getchar(); 
	printf("\x1b[0m");
return;

}
		
(Sorry this below is so hard to read, it was too long to retype,
and I copied it from DevC to the clipboard, to here)

void menu() {
	int choice;
	char buf[2]; <--if you look here, it's 2, then look below
	cls(); 
(skip down reading to right below all the "***********'s")
(that's where the problem is, this stuff in the middle is the main..)
(..menu that I made, which looks horrible posted in this tiny..)
(..window)

	printf("\x1b[34m");
	
	printf("\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n");
	printf("                         ***********Main Menu**********                        ");
	printf("                          *                            *                        ");
	printf("                          *\x1b[31m         1)\x1b[34mRun Story        *                        ");
	printf("                          *                            *                        ");
	printf("                          *                            *                        ");
	printf("                          *                            *                        ");
	printf("                          *                            *                        ");
	printf("                          *\x1b[31m         2)\x1b[34mAbout            *                        ");
	printf("                          *                            *                        ");
	printf("                          *                            *                        ");
	printf("                          *                            *                        ");
	printf("                          *                            *                        ");
        printf("                          *\x1b[31m         3)\x1b[34mExit             *                        ");
	printf("                          *                            *                        ");
        printf("                          ******************************                        ");

	printf("\n\n\n\n");
	printf("                                 Choice:");		
gets(buf,2,stdin); //<----why won't a 1 instead of 2 work here?
	if (sscanf(buf,"%d",&choice) != 1) {
		printf("Please enter a valid selection\n");
		printf("Press <ENTER>\n");
		getchar();
		menu();
		} 
printf("blah");//if got this far, must be number.
return;

oh, I see it came out looking much better once I posted it....

fgets reads 1 *less* than the number of characters you specified. So if you give it 1, it reads 0 characters. Thats why you need the 2.

wow, that makes sense....thanks!

Thanks again for the input, it not works great, but 1 more question, now if the user enters 2 letters, instead of a number, it says "Please enter a valid selection" like it should. However, if they only enter 1 letter and hit enter, it just clears the screen and makes whatever they entered disappear, and repeats the menu, which isn't a big deal, but I'm wondering why...? It's like, if you only enter 1 letter, it goes, cls, menu(), instead of cls, "please enter blah blah blah" like it should....

actually, I just replaced my switch statement with if conditional statements, and things are looking much better, guess I fixed that one on my own

One thing I'd still like to know however, is how to "trap" the cursor...for instance, make it so that when I'm only expecting like 1 letter as input from stdin, they can't keep typing past 1 letter...for instance: Choice:_ and where the underscore is, if they try to type more than that, it can't look like this: Choice:_fjdkfjdkfdjkdfjk, and continue on past and down to the next line....a way so that it(cursor) can only reside in that one blank....ya know?

C has no direct support for such a thing (cursor manipulation).

> a way so that it(cursor) can only reside in that one blank....ya know?
Already answered - http://cboard.cprogramming.com/showthread.php?t=74053

Or read each character yourself (not using fgets to get a whole line for yourself) and use the ANSI escape sequence for moving the cursor.

When you say, already awnsered, well I went back and read what you had written there, but I'm not quite sure I know what you mean. Can you please elaborate?

I mean, what function can do that? Thanks for the help.