fgets, sscanf question.....

This is a discussion on fgets, sscanf question..... within the C Programming forums, part of the General Programming Boards category; The code below is kinda hard to read, it's a portion of a program I'm trying to make for ANSI ...

  1. #1
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    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;

  2. #2
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    oh, I see it came out looking much better once I posted it....

  3. #3
    Registered User freespace's Avatar
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    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.

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    wow, that makes sense....thanks!

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    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....

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    Also, I just noticed, if you enter a really large number, it prints "Invalid Number" over and over, which is what I put in the DEFAULT part of the switch statement that I added under it.
    Last edited by Ash1981; 01-04-2006 at 02:34 AM. Reason: mistake

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    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

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    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?

  9. #9
    cwr
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    C has no direct support for such a thing (cursor manipulation).

  10. #10
    and the hat of wrongness Salem's Avatar
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    > a way so that it(cursor) can only reside in that one blank....ya know?
    Already answered - There must be a way...

    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.

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    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?

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

  13. #13
    Frequently Quite Prolix dwks's Avatar
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    I mean, what function can do that?
    Manipulate the mouse, you mean? Try searching google, or this board for that matter.
    dwk

    Seek and ye shall find. quaere et invenies.

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