c - Should a read from FIFO block after all the data was just read from that FIFO? -

i'm learning pipe programming in linux, , having trouble understanding pipe / fifo management.

i wrote small program opens fifo created (i did mkfifo newfifo in terminal before executing program). repeatedly read , dump character buffer. i'm filling fifo using echo "message" > newfifo terminal's cmd line.

the problem when write fifo, can read data in buffer, read doesn't block anymore. understanding after read data fifo, fifo should empty , read should block. thinking wrong, or incorrectly managing fifo?

code below:

#include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <fcntl.h> #include <sys/types.h>  #define newpipe "./newfifo"  void main() {   int great_success = 0;    int fd;   char buffer[20];    fd = open(newpipe, o_rdonly);    while (1) {     great_success = read(fd, buffer, 20);      if (great_success < 0) {       printf("pipe failed\n");     } else {       printf("buffer : %s\n", buffer);       printf("great_success = %d\n", great_success);       great_success = 0;     }   } } 

your understanding of how fifos works incorrect. pipes: if write end closed (the echo command has terminated), read end read end-of-file (eof), i.e. return 0.

note when open fifo, isn't read blocking. blocking system call open() system call, explained in http://linux.die.net/man/4/fifo