Solved

fgets sscanf buffer

Posted on 2004-08-26
8
1,038 Views
Last Modified: 2008-02-01
Hi..

there s a problem with scanf when reading a string to char array... if the length of input is greater than the allocated size of the character array..

somebody in the group posted..
fgets , sscanf and the below functions can be used instead of scanf.
void clearbuffer()
{
   int junk;
   do
   {
      junk = getchar();
   } while (junk != '\n' && junk != EOF && junk != '\0');
}

can anyone explain ?
0
Comment
Question by:manojantony
8 Comments
 
LVL 55

Accepted Solution

by:
Jaime Olivares earned 30 total points
Comment Utility
This function is not intended for what you want to do. It only reads pending character in keyboard buffer, it is used before calling an input function to avoid typing errors.

you can use fgets() to read an entire line limiting size, so buffer size will be not a problem.
If the line you read have many values you want to "scanf" then use sscanf():

#define MAX_SIZE 1000

char buffer[MAX_SIZE];
fgets(buffer, MAX_SIZE, stdin);  /* reads from standard input (console) */

Optionally:
sscanf(buffer, "%i %f %s", &myInteger, &myFloat, anotherCharBuffer);
0
 
LVL 1

Author Comment

by:manojantony
Comment Utility
Yes thats fine .. but .. I am not able to clear the buffer.

Suppose the MAX_SIZE is 10 and am enetring 13 characters. In the buffer there will not be any '\n' as well as '\0'. Also 3 characters are extra.

And if am not able to clear the buffer, those 3 will be coming in the next output.

I hope the question is clear.

whats the solution ?
 
0
 
LVL 1

Author Comment

by:manojantony
Comment Utility
Am asking ... If there is an overflow in fgets ... how to eliminate the unwanted characters in buffer ?

Can u please illustrate with example ?
0
 
LVL 55

Expert Comment

by:Jaime Olivares
Comment Utility
you can use:
    fflush(stdin);

or you can use the clearbuffer() function you posted.

This must be done just before the fgets() line.
0
How your wiki can always stay up-to-date

Quip doubles as a “living” wiki and a project management tool that evolves with your organization. As you finish projects in Quip, the work remains, easily accessible to all team members, new and old.
- Increase transparency
- Onboard new hires faster
- Access from mobile/offline

 
LVL 7

Expert Comment

by:aib_42
Comment Utility
Bear in mind that fflush(stdin) causes undefined behaviour on some systems, and that there is no standard way to flush the input buffer. Taking a look at the available ioctl() calls might help, as might jaime's suggestions do.
0
 
LVL 2

Assisted Solution

by:sneeuw_chan
sneeuw_chan earned 20 total points
Comment Utility
The 'clean' way to do this would be to make a function that allocates as much memory as you need to read an entire line no matter what the length is.  Lots of systems already have a function like that, for example BSD has an fgetln() function.  If not, you can quite easily make a small routine yourself that uses fgets and realloc to read lines as long as the user types them.
0
 
LVL 1

Author Comment

by:manojantony
Comment Utility
Hey . what if the fgets is accepting inputs which is invalid format for scanf.

Some buffer management has to be there?
0
 
LVL 55

Expert Comment

by:Jaime Olivares
Comment Utility
It is the same effect than use scanf, string is not evaluated until user presses enter.
sscanf returns number of arguments processed correctly, so it is a primary kind of control.
0

Featured Post

Better Security Awareness With Threat Intelligence

See how one of the leading financial services organizations uses Recorded Future as part of a holistic threat intelligence program to promote security awareness and proactively and efficiently identify threats.

Join & Write a Comment

Preface I don't like visual development tools that are supposed to write a program for me. Even if it is Xcode and I can use Interface Builder. Yes, it is a perfect tool and has helped me a lot, mainly, in the beginning, when my programs were small…
This is a short and sweet, but (hopefully) to the point article. There seems to be some fundamental misunderstanding about the function prototype for the "main" function in C and C++, more specifically what type this function should return. I see so…
Video by: Grant
The goal of this video is to provide viewers with basic examples to understand and use while-loops in the C programming language.
The goal of this video is to provide viewers with basic examples to understand and use switch statements in the C programming language.

763 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

12 Experts available now in Live!

Get 1:1 Help Now