UNIX for Advanced & Expert Users

Hi,
I wrote a program, to read from a master terminal.
However, the 'read' system call keeps returning the same data endlessly (I expected it to read once and then block).
What will cause t data to be flushed, after 1 read?

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <fcntl.h>

int main()
{
int fd, cfd;
char *path;
char s[20];

memset(s, 0, 20);

fd = open("/dev/ptmx", O_RDWR);

printf("fd is %d\n", fd);

grantpt(fd);
unlockpt(fd);

path = ptsname(fd);

while(read(fd, s, 19)) /* this 'read' reads t same data again n again. I expect it to block after 1 read */
{
printf("Read %d:%s\n", strlen(s), s);
}

return (0);
}

---------- Post updated at 08:19 PM ---------- Previous update was at 08:13 PM ----------

n just to add, i do
echo > /dev/pts/X,
where X corresponds to the slave pts.

its after this that t read goes on infinitely.

---------- Post updated at 09:14 PM ---------- Previous update was at 08:19 PM ----------

sorry guys......... a stupid mistake of not reading t output from 'read' :P

Your read() call probably returned -1 and didn't modify the contents of the buffer.