Scansets

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Scansets

 
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  #1
Aug 30th, 2006
I'm trying to use scansets to filter out out some textfiles.[/COLOR]

C Syntax (Toggle Plain Text) 
  1. #include <stdio.h>
  2. int main( void)
  3. {
  4.    int i;
  5.    char str[ 80], str2[ 80];
  6.    scanf("%d %[abcdefg] %s", &i, str, str2);
  7.    printf("%d %s %s", i, str, str2);
  8.    getchar();
  9.    return 0;
  10. }

When I input "123abcdtye" I expect the output to be "123 abcd tye". Instead my program exits as if it reaches the return statement even though I have put in a getchar() to pause the program. What is going on?
Last edited by Dave Sinkula; Aug 30th, 2006 at 9:30 pm. Reason: fixed format and deleting some spaces added when pasting ## Fixed the fix.
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Re: Scansets

 
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  #2
Aug 30th, 2006
Hi VinC,
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#include <stdio.h>
int main( void)
{
int i;
char str[ 80], str2[ 80];
scanf("%d %[abcdefg] %s", &i, str, str2);
printf("%d %s %s\n", i, str, str2);
system("pause");
return 0;
}
Use
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system("pause");
instead.
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Re: Scansets

 
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  #3
Aug 30th, 2006
Code is fine and it works as expected in my compiler(gcc 3.4.5).
Try using some other input mechanism which doesn't leave stuff back in the input stream.
Last edited by Grunt; Aug 30th, 2006 at 1:11 pm.
The key to eliminating bugs from your code is learning from your mistakes.
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Re: Scansets

 
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  #4
Aug 30th, 2006
Ok that's weird. Using system("PAUSE") gives me the correct output but why is this? It seems to me that they should be equivalent in this situation but apparently I have a misunderstanding.

I've been taught to use getchar() over system("PAUSE)http://www.gidnetwork.com/b-61.html

I'm using Dev-C++
Last edited by VinC; Aug 30th, 2006 at 1:08 pm. Reason: include compiler
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Re: Scansets

 
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  #5
Aug 30th, 2006
Did it manage to work with getchar() or system("PAUSE")?
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Re: Scansets

 
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  #6
Aug 30th, 2006
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Originally Posted by mostafadotnet View Post
Hi VinC,
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system("pause");
Use instead.
No, don't. Learn your tools. Using scanf() to read characters is even worse than using gets() because not only does it allow you to blow your buffer boundaries but as you can see it also leaves your input stream dirty. The \n is left in the stream for your getchar() to read.

Use a combination of fgets() and sscanf() for safety and to process the input stream cleanly.
C Syntax (Toggle Plain Text) 
  1.     fgets(tmpstr, 80, stdin);
  2.     sscanf(tmpstr,"%d %[abcdefg] %s", &i, str, str2);
[edit]Since you already learned this from GID, you could check out the scanf() series there. [/edit]
Last edited by WaltP; Aug 30th, 2006 at 1:25 pm.
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Re: Scansets

 
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  #7
Aug 30th, 2006
Thank you for all the help!
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Re: Scansets

 
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  #8
Aug 30th, 2006
> gives me the correct output but why is this?
Because scanf() is full of wonderful surprises - the most usual being that it leaves the \n on the input stream - just ready for the getchar() to return with immediate success.

I'd suggest you ALWAYS use fgets() to read a line of input, then use sscanf() (or something else) to extract information from the buffer.
fgets() leaves the input stream in a far more consistent state than scanf() ever can.

C Syntax (Toggle Plain Text) 
  1. char buff[BUFSIZ];
  2. if ( fgets( buff, sizeof buff, stdin ) != NULL ) {
  3.   if ( sscanf( buff, "%d %[abcdefg] %s", &i, str, str2) == 3 ) {
  4.     printf("%d %s %s\n", i, str, str2); 
  5.   } else {
  6.     // some error
  7.   }
  8. }
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Re: Scansets

 
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  #9
Aug 30th, 2006
[edit]Since you already learned this from GID, you could check out the scanf() series there. [/edit][/quote]

Will do. I couldn't help but notice that the author of the articles on GID is also WaltP! :eek:
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Re: Scansets

 
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  #10
Aug 30th, 2006
Hi all,
I've just suggested the easiest and the worst way to use when you have windows running.
Simply,i don't recommend it for your commercial&/ important projects.

Good luck.
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