c1-2 copy from stadin to stdout

#include "apue.h"

#define  BUFFSIZE 4096

int main(void )
{
    int n;
    char buf[BUFFSIZE];

    while( (n = read(STDIN_FILENO,buf,BUFFSIZE) ) > 0)
        if(write(STDOUT_FILENO,buf,n) != n )
            err_sys("write error");
    exit(0);
}

print the stdin to stdout 

PS:

STDOUT_FILENO---------------->1

STDIN_FILENO----------------->0

STDERR_FILENO----------------->2