Problem with input stream

Hi all,

I have two doubts relating to the following code.

Code:

---

#include <stdio.h>

int main(void)
{
    int i;
    char c;
    printf("Enter some integer value:");
    scanf("%d",&i);
    __fpurge(stdin);
    printf("Enter some character:");
    scanf("%c",&c);
    printf("Input values are %d and %c\n",i,c);
    return 0;
}

---

1. In the above code if i remove the fpurge() function then i am not able to input the character (i.e.,) the scanf() for getting the character got skipped
2. When i look into the man page for fpurge() it states that this function is not a standard one and also not portable, so i thought i can use fflush(stdin) but when i used fflush instead of fpurge the code works the same way i discussed in first step.

Why is this behaviour happening?

fflush(stdin) has undefined behaviour.

So in this case, if i want to come up with a standard as well as portable code then what shall i use in the place of fpurge() function. Any clues?

I am finding the FAQ has answers to questions like this

How do I get a number from the user (C)

It really is helping me out. Maybe it will help you too.

Quote:

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Originally Posted by cbalu

2. When i look into the man page for fpurge() it states that this function is not a standard one and also not portable, so i thought i can use fflush(stdin) but when i used fflush instead of fpurge the code works the same way i discussed in first step.

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fflush is meant for use on stdin, read the man page:

Quote:

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The function fflush() forces a write of all user-space buffered data
for the given output or update stream via the stream’s underlying write
function.

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stdin is an input stream, so you now have undefined behavior. Even if it seems to work don't do it! The same is probably true of fpurge, whoever wrote that code was being ignorant.

If you want to learn how to deal with this issue properly read this:

STDIN pitfalls

It will take you about 10 minutes to achieve enlightenment ;)

MK27 thanks for your thoughts i will look at the link which you posted.

Quote:

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whoever wrote that code was being ignorant

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Ofcourse it was non other than me. I was trying some other thing and landed with this problem so started searching for solution online and found out this was working.

Quote:

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Originally Posted by cbalu

Ofcourse it was non other than me. I was trying some other thing and landed with this problem so started searching for solution online and found out this was working.

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It's not your fault, this "ignorance" is propagated online, etc. But now you know!

By the way, looks like the link which you pointed out was written by you, great explanation.

Thanks for making it crystal clear.

Quote:

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Originally Posted by cbalu

By the way, looks like the link which you pointed out was written by you, great explanation.

Thanks for making it crystal clear.

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Yes, that's me :) This is probably the most common problem that comes up here, which is why I wrote that (thanks for the compliment, glad you liked it).