About c : C-pipe-does-not-work-if-I-use-multiple-files

I’m still new to pipes and I want to understand why this is not working.

Assuming I have the following :

main.c :

#include "macros.h"
#include "child_parent.h"

int main()
{
    if (pipe(pipefd) == -1)
    {
        perror("pipe");
        exit(EXIT_FAILURE);
    }

    switch(fork())
    {
        case -1:
            perror("fork()");
            exit(EXIT_FAILURE);

        case 0:
            return child();

        default:
            return parent();
    }
}

child_parent.c :

#include "macros.h"
#include "child_parent.h"

int child()
{
    char buf;
    close(pipefd[1]); // Close unused write end

    while(read(pipefd[0], &buf, 1) > 0)
        CHECK(write(STDOUT_FILENO, &buf,1),"write1()");

    CHECK(write(STDOUT_FILENO, "\n" , 1),"write2()");
    close(pipefd[0]);

    return EXIT_SUCCESS;
}

int parent()
{
    const char *msg = "Hello world!\n";

    close(pipefd[0]); // Close unused read end
    CHECK(write(pipefd[1], msg, strlen(msg)),"write3()");
    close(pipefd[1]);

    wait(NULL);

    return EXIT_SUCCESS;
}

child_parent.h :

#pragma once

static int pipefd[2];

int child();
int parent();

macros.h

#pragma once

#define CHECK(func, msg) do {       \
    if ( (func) == -1) {            \
        perror(msg);                \
     }                              \
    }while(0)                       \

So basically I just wanted to test the inter-process communication between anonymous pipes. When compiling the program, it throws the following error:

write3(): Bad file descriptor

Which means that the parent process couldn’t write into the pipe.

But when writing the whole implementation in main.c, the communication will work correctly.

So it has to do with the static int pipefd[2] that is declared in child_parent.h.
What am I doing wrong here ?