Implicit declaration of function ‘mknod’ but I have the headers included

I am trying to make a C program that uses named pipes to communicate with a C++ program on a Raspberry Pi 3.

The warning that GCC is spitting out when I compile some code of mine:

/home/pi/BluetoothTest/btooth.c|76|warning: implicit declaration of function ‘mknod’ [-Wimplicit-function-declaration]|

Here is the code from for the function, including the #if above it:

#if defined __USE_MISC || defined __USE_BSD || defined __USE_XOPEN_EXTENDED
extern int mknod (const char *__path, __mode_t __mode, __dev_t __dev)
     __THROW __nonnull ((1));

and here are the includes that I have in the file:

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <pthread.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <bluetooth/bluetooth.h>
#include <bluetooth/hci.h>
#include <bluetooth/hci_lib.h>
#include <bluetooth/rfcomm.h>
//#include <linux/stat.h>

The program attempts to create the pipe here:

umask(0);
fifo = mknod(PIPE_LOC, S_IFIFO|0666, 0);
fp = fopen(PIPE_LOC, "w");

fifo is an int that isn't used anywhere else and fp is a FILE* to the pipe. Some debugging that I have done shows that fifo has a value of -1 after mknod runs, likely because of the compiler not seeming to be able to find the implementation of the function.

How do I make it so that GCC knows where to find the implementation of mknod?

Solution

As you can see that for declaration of mknod() function to stay after preprocessing stage, one of three macros (__USE_MISC, __USE_BSD, __USE_XOPEN_EXTENDED) should be defined. Otherwise, declaration of mknod() will be removed during preprocessing stage.

#if defined __USE_MISC || defined __USE_BSD || defined __USE_XOPEN_EXTENDED
extern int mknod (const char *__path, __mode_t __mode, __dev_t __dev)
 __THROW __nonnull ((1));

You can use compiler options: -std=gnu99 -D_GNU_SOURCE or you can define these macros on your own and place them above header file inclusion.