Process reads data before writing into pipe - unix

Question

I am trying to create pipe and use it with fork(). But I m confused in the order of execution.
Process reads data from pipe before anything is written into pipe. Sometimes it runs correctly. But sometimes, reads before writing but still gives correct output.
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
int main(void)
{
int fd[2], nbytes,ret;
pid_t childpid;
char string[] = "Hello, world!\n";
char readbuffer[80];
pipe(fd);
if(!fork())
{
close(fd[0]);
printf("Writing...");
write(fd[1], string, (strlen(string)+1));
exit(0);
}
else{
close(fd[1]);
printf("Reading...");
nbytes = read(fd[0], readbuffer, sizeof(readbuffer));
printf("Received string: %s", readbuffer);
wait(NULL);
}
return 0;
}

Answer 1

It happens because scheduler schedules the parent process before the child and thus
it results in the read operation before write. On the other hand, the output may be
as expected sometimes when scheduler will schedule the child first.
SOLUTION:
1. you need to use synchronisation techniuqes like semaphores in order to synchronise the
parent and the child.
2. or you can make the parent process wait until the child has finished. Consider the
following code :
int child_status; // declare this variable
/* add the following line to the else clause */
else
{
close(fd[1]);
wait(&child_status);
// rest of your code
}
Explanation :
If the parent process is scheduled before the child, then its execution will halt when
it finds the 'wait(&child_status)' statement and will wait for the child to finish
its execution and then proceed further.