c10-19--system call withour signal handler

#include "apue.h"
static void
sig_int(int signo)
{
    printf("caught sigint\n");
}
static void
sig_chld(int signo)
{
    printf("caught sigchld\n");
}
int main(void)
{
    if (signal(SIGINT,sig_int) == SIG_ERR)
        err_sys("sig_int error");
    if (signal(SIGCHLD,sig_chld) == SIG_ERR)
        err_sys("sig_chld error");
    if (system("/bin/ed") < 0)
        err_sys("system error");
    exit(0);
}

#include <sys/wait.h>
#include <errno.h>
#include <unistd.h>

int system(const char * cmdstring) /*version without signal handling */
{
    pid_t pid;
    int status;

    if (cmdstring == NULL)
        return(1);  /* always a command preocessor with unix */
    if ( (pid = fork()) < 0) {
        status = -1; /* probably  out of processor */
    } else if (pid == 0) {   /* child porcess */
        execl("/bin/sh","sh","-c",cmdstring,(char *) 0 );
        _exit(127); /* execl error */
    } else {
        while ( waitpid(pid,&status,0) < 0) {
            if (errno == EINTR) {
                status = -1; /* error other than sintr from waitpid */
                break;
            }
        }
    }
    return(status);
}

output of the program :

gcc -Wall -o c10-19 c10-19.c signal l.o error.c system.c
ubuntu@ubuntu-virtual-machine:~/Desktop/apue$ ./c10-19
a
hello. ,world
.
1,$p
hello,world
w temp.too
12
q
caught sigchld
ubuntu@ubuntu-virtual-machine:~/Desktop/apue$ ./c10-19
a
hello,wol rld
1,4p  4 $p
.
1,$p
hello,world
1,$p
w temp.to  foo
17
^Ccaught sigint
 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
?
^Ccaught sigint
 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
?
q
caught sigchld
system系统调用没有处理SIGCHLD,SIGINT,导致父子进程均受到该信号，而产生上面的输出，唯一和原文不一致的地方在于用xXXX表的行，一个空白行，书上没有，不知道什么原因，估计是shell产生的输入，shell本身是忽略这两个信号的，不知道这个猜测对不对？

进程如图所示：

fork              fork               fork

sehll--------->c10-20----------->shell -------------> ed

ps -o pid,ppid,commd
  PID  PPID COMMAND
 2610  2437 bash
 3267  2610 c10-20
 3268  3267 sh
 3269  3268 ed
 3273  2610 ps