C can't read from fifo (named pipe)

Question

I create a fifo, but i can't read from it. What's the problem? Here is a code and output. If I use O_RDONLY without O_NONBLOCK program just wait.

pid_t p;
int fd;
char str[]="sample";

mkfifo("myfifo", S_IRUSR | S_IWUSR);

fd = open("myfifo", O_RDWR);

printf("write %d byte\n", write(fd, str, 5));

close(fd);

fd = open("myfifo", O_RDONLY | O_NONBLOCK);

printf("read %d byte\n",read(fd, str, 6));

close(fd);

unlink("myfifo");

Output:

write 5 byte
read 0 byte

Answer 1

1. Issue is your closing the file,

you can try this or fork another process and read the file, which is mostly why named fifos are used for i.e inter-process communication

This link explains in detail How to send a simple string between two programs using pipes?

pid_t p;
int fd;
char str[]="sample";

mkfifo("myfifo", S_IRUSR | S_IWUSR);

fd = open("myfifo", O_RDWR);

printf("write %d byte\n", write(fd, str, 5));

printf("read %d byte\n",read(fd, str, 6));

close(fd);

unlink("myfifo");