The setup:
exerciser - A program that prints some stuff, and launches a child process that also prints some stuff.  Their prints are setup so that both processes could have the "A" buffered unless stdout is flushed before the fork.
reader - Launches a child process and sets up a pipe to read it's output.  Prints immediately everything it reads from the child.  The child runs the exerciser program.

The problem:
The terminal somehow deals with the exerciser in a smart way that prevents "A: 10" from showing up twice, the poor reader on the other hand gets "A: 10".  What does *reader* have to do differently so that it gets the exact same result as what the terminal shows?

NOTE: I know how to fix this by adding flushes to exerciser but a part of the problem is that I must solve this by only altering reader.

----terminal output----
<...>/pipe-testing$ ./exerciser
A: 10
B: 42
C: 42
C: 10
<...>/pipe-testing$ ./reader
READER...
A: 10
B: 42
C: 42
A: 10
C: 10

----exerciser.cpp----
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

int main(){
    int n = 10, status = 0;
    fprintf(stdout, "A: %d\n", n);
    if (fork() == 0){
        n = 42;
        fprintf(stdout, "B: %d\n", n);
    }
    else{
        wait(&status);
    }
    fprintf(stdout, "C: %d\n", n);
    return(0);
}

----reader.cpp----
#include <stdio.h>
#include <unistd.h>

int main(){
    fprintf(stdout, "READER...\n");
    fflush(stdout);

    int pipe_fds[2];
    if (pipe(pipe_fds) == -1){
        fprintf(stdout, "failed to make pipe\n");
        return(0);
    }

    pid_t child_pid = fork();
    if (child_pid == -1){
        fprintf(stdout, "failed to fork\n");
        return(0);
    }

#define PIPE_READ 0
#define PIPE_WRITE 1

    if (child_pid == 0){
        close(pipe_fds[PIPE_READ]);
        dup2(pipe_fds[PIPE_WRITE], STDOUT_FILENO);
        dup2(pipe_fds[PIPE_WRITE], STDERR_FILENO);

        char *argv[] = {
            "sh",
            "-c",
            "./exerciser",
            0
        };

        if (execv("/bin/sh", argv) == -1){
            fprintf(stdout, "failed to execv\n");
            return(0);
        }
    }
    else{
        close(pipe_fds[PIPE_WRITE]);

        char buffer[1024];
        int capacity = sizeof(buffer);
        for (;;){
            ssize_t num = read(pipe_fds[PIPE_READ], buffer, capacity);
            if (num == -1){
                fprintf(stdout, "read error\n");
                return(0);
            }
            else if (num == 0){
                break;
            }
            else{
                fprintf(stdout, "%.*s", (int)num, buffer);
                fflush(stdout);
            }
        }
    }

    return(0);
}