Create and write function for pipe for usage in main() - c

Question

The 'create_andWrite' function should create a pipe and write a string to it. The child process which is created in the main should read from the pipe.
I only worked with pipes in one method(e.g. read and write are both in main) before and I'm really struggling with this one.
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
int creat_and_write(FILE *fd, char *string) {}
int main() {
int fd[2];
creat_and_write();
int p = fork;
}
These are my functions signatures so far

Answer 1

Pipes are one way of unidirectional IPC, used usually with fork() to pass data in a sort of vertical hierarchy.
Hope the example below is clear. and spot the usage of the 2 functions.
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#define READ_END 0
#define WRITE_END 1
// pipe uses file descriptors to communicate between processes not pointers to files.
int creat_and_write(int *fd, char *string) {
// first and formost we need a pipe.
if (pipe(fd) == -1) {
perror("pipe error");
exit(1);
}
// now the fd contains 2 file descriptors, one for reading and one for writing to the pipe.
// we fork a child process which will inherit most internals including the pipe's file descriptors.
pid_t pid = fork();
if (pid == -1)
{
perror("fork error");
exit(1);
}
else if (pid == 0)
{
// we're at the child process.
// now we can write to the write end of the pipe
write(fd[WRITE_END], string, strlen(string));
// good practice to close done end of the pipe. for a full cleanup.
close(fd[WRITE_END]);
}
else
{
// we're at the parent process.
// now we can read from the read end of the pipe
char buffer[strlen(string)];
read(fd[READ_END], buffer, 100);
close(fd[READ_END]);
printf("now at the parent process: %s\n", buffer);
}
return 0;
}
int main() {
int fd[2];
creat_and_write(fd, "msg from child process");
return 0;
}