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Old 04-24-2006, 11:55 AM   #1
ionuion
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Registered: Dec 2004
Location: Moldova
Distribution: slackware
Posts: 5

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scanf doesn't interrupt flow to read input


hello.
The idea behind my program is to get some numbers to send it asynchronously to a process. The decimals are red from the keyboard.

Code:
#include <stdio.h>

int main(void)
{
	printf("We need integer values. Could you provide us some, please?\n");
	printf("Press Ctrl-C when you have no more to give\n");
	while(1)
	{
		int temp;
		printf("Number? :");
		int ret = scanf("%d", &temp);
                // ferror associated to stdin is 0 at this point  
		if (!ret)
		{
			printf("This might not be a number.\n");
			printf("Please try again. What about right now?\n");
			continue;
		}
		else
		{
			// Good data. Can send them as useful
		}
	}
}
So, if the user sends an "it", the input shall be ignored, and user prompted for another number. At least that's what I expect. The fact is once an errouneous input is provided, the program behaves as the line containing the call to scanf didn't exist.
I tried to read ferror(stdin). It is 0 in any case.

Any hints will be endlessly appreciated.

Linux 2.6.14.2 PREEMPT i686 GNU/Linux
gcc (GCC) 3.3.6 (Debian 1:3.3.6-13)
 
Old 04-24-2006, 05:22 PM   #2
Mara
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Registered: Feb 2002
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That's how scanf() works. In your case, you should read a line as string (using getchar, fgets or read), then use atoi to convert it to a number and that, looking at the result, print the message or deal with the number you have.
 
Old 04-24-2006, 06:21 PM   #3
ioerror
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Registered: Sep 2005
Location: Old Blighty
Distribution: Slackware, NetBSD
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scanf is a function I try to steer clear of.

Quote:
then use atoi to convert it to a number
Better to use strtol, since atoi doesn't detect errors.
 
Old 04-25-2006, 08:45 AM   #4
ionuion
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Registered: Dec 2004
Location: Moldova
Distribution: slackware
Posts: 5

Original Poster
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Thank you for your help. I'll look with another pair of eyes at the scanf family.

Regards.
 
  


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