Ask the experts about the named pipeline (fifo): one error is that debugging fails.

Ask the experts about the named pipeline (fifo): An error is that debugging fails-Linux general technology-Linux technology and application information. For details, refer to the following. Today, I debugged a program related to the pipeline, but I haven't been playing it out for half a day. Ask the experts:
The pipeline is successfully established, that is, an error occurred while opening the pipeline ~
Error message: No such device or address
What is the problem? Thank you!
# Define WFIFO "writefifo"

Char buf [256];
Int w_fd;
Struct stat stat_buf;

Printf ("begin to create writefifo \ n ";
Int ret = mkfifo (wfirst, 0666 );
Printf ("ret = % d \ n", ret );
If (ret =-1 ){
Printf ("Fail to create fifo % s: % s \ n", WFIFO, strerror (errno ));
Exit (-1 );
}

Strcpy (buf, s );
Printf ("buf: % s \ n", buf );
Printf ("get w_fd \ n ";
W_fd = open (WFIFO, O_WRONLY | O_NONBLOCK );
Printf ("writefifo's fd: % d \ n", w_fd );
If (w_fd =-1 ){
Printf ("Fail to open fifo % s: % s \ n", WFIFO, strerror (errno ));
Exit (-1 );
}

This is the intermediate pipeline code, which is an error in w_fd = open (WFIFO, O_WRONLY | O_NONBLOCK,
Error message: Fail to open writefifo: No such device or address;
If this sentence is changed to w_fd = open (WFIFO, O_RDONLY | O_NONBLOCK); it will be okay, but I want to open it in writing ~
Which expert can give me some advice ~~