Unable to open FIFO for writing

Question

'Server' program side:

#define RESP_FIFO_NAME "response"

/* Global Variables */
char *cmdfifo = CMD_FIFO_NAME; /* Name of command FIFO. */
char *respfifo = RESP_FIFO_NAME; /* Name of response FIFO. */

int main(int argc, char* argv[]) {
int infd, outfd; /* FIFO file descriptors. */

... // blah blah other code here

/* Create command FIFO. */
if (mkfifo(cmdfifo, FIFO_MODE) == -1) {
    if (errno != EEXIST) {
        fprintf(stderr, "Server: Couldn’t create %s FIFO.\n", CMD_FIFO_NAME);
        exit(1);
    }
}

/* Create response FIFO. */
if (mkfifo(respfifo, FIFO_MODE) == -1) {
    if (errno != EEXIST) {
        fprintf(stderr, "Server: Couldn’t create %s FIFO.\n", RESP_FIFO_NAME);
        exit(1);
    }
}
/* Open the command FIFO for non-blocking reading. */
if ((infd = open(cmdfifo, O_RDONLY | O_NONBLOCK)) == -1) {
    fprintf(stderr, "Server: Failed to open %s FIFO.\n", CMD_FIFO_NAME);
    exit(1);
}

        /* Open the response FIFO for non-blocking writes. */
if ((outfd = open(respfifo, O_WRONLY | O_NONBLOCK)) == -1) {
            fprintf(stderr, "Server: Failed to open %s FIFO.\n", RESP_FIFO_NAME);
            perror(RESP_FIFO_NAME);
            exit(1);
        }

The program prints an output of:

Server: Couldn’t create response FIFO.

I understand very little on FIFOs as my professor didn't teach it. This was all I was able to manage from reading his examples and lecture notes. I tried without O_NONBLOCK flag but that just causes the program to hang, so it is required. I don't understand why the read FIFO is fine but the write FIFO fails to open.

Answer 1

From the man-page :

A process can open a FIFO in non-blocking mode. In this case, opening for read only will succeed even if noone has opened on the write side yet; opening for write only will fail with ENXIO (no such device or address) unless the other end has already been opened.

You should open this one in the 'client'.