打开命名管道的问题

Question

I've run into a problem while trying to send data through pipes, to be more exact: i do not get non-null file descriptors for pipe. Here is the code for creation of the pipe:

//PIPE is defined as a "/tmp/my.fifo"
umask(0);
...
mknod(PIPE,S_IFIFO,0);
...
p=fopen(PIPE,"w");
if (p)
{
    //fprintf(p,"some message");
    fclose(p);
}
else
    printf("Could not open the pipe\n");

Here is the code for reading from the pipe:

cos_pipe = fopen(PIPE,"r");
if (cos_pipe)
{
    fgets(buffer,80,cos_pipe);
    ...
    fclose(cos_pipe);
}
else
{
    printf("Couldn't open the pipe\n");
    usleep(300000);
}

Code is compiled into two different bineries that i launch separately. All the output i get is "Couldn't open the pipe".

On somewhat related note: should the program that created pipe delete it later?

Answer 1

The mode argument requires permissions too. Use S_IFIFO|S_IRUSR|S_IWUSR .

Consider using the mkfifo function instead:

mkfifo(PIPE,S_IRUSR|S_IWUSR)

You should remove the pipe when you are done using it. Also, what happens if more than one instance of your program is running at once - you're using a fixed name for the pipe.