c - I am not able to flush stdin

How to flush the stdin??

Why is it not working in the following code snippet?

#include 
#include 

#include 
#include 

int main()
{
        int i=0,j=0, sat;
        char arg[256];
        char * argq;
        argq = malloc(sizeof(char)*10);


        printf("Input the line\n");
        i=read(0, arg, sizeof(char)*9);
        arg[i-1]='\0';
        fflush(stdin);

        i=read(0, argq, sizeof(char)*5);
        argq[i-1]='\0';

        puts(arg);
        puts(argq);


        return 0;
}

Now if i give the input as 11 characters, only 9 should be read but the remaining two characters in the stdin are not flushed and read again in the argq. Why?

Input:
123 456 789

Output:
123 456
89

Why am i getting this 89 as the output?

Answer

I believe fflush is only used with output streams.

You might try fpurge or __fpurge on Linux. Note that fpurge is nonstandard and not portable. It may not be available to you.

From a Linux fpurge man page: Usually it is a mistake to want to discard input buffers.

The most portable solution for flushing stdin would probably be something along the lines of the following:

int c;
while ((c = getchar()) != '\n' && c != EOF);