What am I missing? stdout isn't working as expected. Or does exec have something to do with it

Question

EDIT: Using fflush(stdout) does not seem work.

The program takes a command line argument when run and gives the man page of the argument in a new Xterm window.

eg: ./a.out ls should give a new window displaying the man page of ls.

NOTE: The only difference between the two programs is line #11.

The code sample given below works as expected.

int main(int argc, char* argv[])
{
    int fd[2];
    pipe(fd);

    pid_t pid = fork();
    if(pid > 0)
    {
        dup2(fd[1], 1);
        close(fd[0]);
        execlp("echo", "echo", argv[1], NULL);
        wait(NULL);
    }
    else
    {
        dup2(fd[0], 0);
        close(fd[1]);
        execlp("xargs", "xargs", "xterm", "-hold", "-e", "man", NULL);
        exit(0);
    }
    return 0;
}

But the code below doesn't work the same:

int main(int argc, char* argv[])
{
    int fd[2];
    pipe(fd);

    pid_t pid = fork();
    if(pid > 0)
    {
        dup2(fd[1], 1);
        close(fd[0]);
        printf("%s", argv[1]);
        fflush(stdout);
        wait(NULL);
    }
    else
    {
        dup2(fd[0], 0);
        close(fd[1]);
        execlp("xargs", "xargs", "xterm", "-hold", "-e", "man", NULL);
        exit(0);
    }
    return 0;
}

The PARENT process pipes the command line argument and the CHILD process takes stdin from the pipe which exec command uses to run.

Shouldn't printf() also give output onto stdout?