How to make a fifo in C? - linux

Question

I have to use mkfifo in my C program in Ubuntu. But I have an error when I compile: no such file or directory .
I think the problem because I have not set the panel_fifo environment variables. But I don't khow how could I do this.
Here is my code I use to test this method:
char *myfifo="./sock/myfifo";
if (mkfifo(myfifo,0777)<0)
perror("can't make it");
if (fd=open(myfifo,O_WRONLY)<0)
perror("can't open it");
I compile this with:
gcc gh.c -o gh
When I run, I get this error message:
can't make it:no such file or directory
can't open it:no such file or directory

Answer 1

It's because the directory sock doesn't exist.
In a terminal:
christian#fujiu1404:~/tmp/t2$ ls
t2.c
christian#fujiu1404:~/tmp/t2$ cat t2.c
#include <fcntl.h>
main() {
int fd;
char *myfifo="./sock/myfifo";
if (mkfifo(myfifo,0777)<0)
perror("can't make it");
if (fd=open(myfifo,O_WRONLY)<0)
perror("can't open it");
}
christian#fujiu1404:~/tmp/t2$ cc t2.c
christian#fujiu1404:~/tmp/t2$ ./a.out
can't make it: No such file or directory
can't open it: No such file or directory
christian#fujiu1404:~/tmp/t2$ mkdir sock
christian#fujiu1404:~/tmp/t2$ ./a.out
Note the program hasn't completed, but your fifo does exist.
Now in a second terminal, put a string into the fifo
christian#fujiu1404:~/tmp/t2$ ls -l sock/
total 0
prwxrwxr-x 1 christian christian 0 May 27 06:45 myfifo
christian#fujiu1404:~/tmp/t2$ echo abc >sock/myfifo
Note echo also is suspended
Now in a third terminal, read from the fifo
christian#fujiu1404:~/tmp/t2$ cat sock/myfifo
abc
christian#fujiu1404:~/tmp/t2$
Note now all programs complete and exit (in all terminals)

Answer 2

You try
myfifo("./sock/myfifo", ...)
You get
no such file or directory
which is ENOENT.
You then want to look up the relevant documentation and find the following in man 3 mkfifo:
ERRORS
[...]
ENOENT A directory component in pathname does not exist or is a dangling symbolic link.
From all this one could conculde ./sock does not exist.