signal handler处理函数在哪个进程中运行？

我在父进程中向子进程发一个信号，执行信号处理函数。
然而函数中getpid()得到的pid仍然是父进程的。
这是怎么一回事呢，不应该是接受到信号的子进程来调用函数处理吗？

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <signal.h>
#include <sys/types.h>
int main()
{
    printf("This is farther process,my pid is %d, before signal\n",getpid());
    int i,j,k,status;
    int func();
    signal(18,func());  /*设置18号 信号的处理程序*/
    while((i=fork())==-1);
    if(i==0)
    {
        //子进程执行
        sleep(6);
        printf("Child %d: A signal from my parent is recived.\n",getpid());
    }
    else
    {
        //父进程执行
        j=kill(i,18);   /*向子进程发送信号18*/
        printf("Parent: signal 18 has been sent to child %d,returned %d.\n",i,j);
        k=wait(&status);      //等待子进程结束
        printf("After wait %d,Parent %d: finished.\n",k,getpid());
        exit(0);
    }
}

int func() /*处理程序*/
{
    printf("I am Process %d: It is signal 18 processing function.\n",getpid());
    return 0;
}

没问题，是子进程调用的

This is farther process,my pid is 84191, before signal
Parent: signal 18 has been sent to child 84192,returned 0.
I am Process 84192: It is signal 18 processing function.
Child 84192: A signal from my parent is recived.
After wait 84192,Parent 84191: finished.

uname -a
Linux server 3.13.0-83-generic #127~precise1-Ubuntu SMP Fri Mar 11 12:53:08 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

#include
#include
#include
#include
#include
#include

int main()
{
printf("This is farther process,my pid is %d, before signal\n",getpid());
int i,j,k,status;
void func(int signo);
signal(18,func); /*设置18号 信号的处理程序*/
while((i=fork())==-1);
if(i==0)
{
//子进程执行
sleep(6);
printf("Child %d: A signal from my parent is recived.\n",getpid());
}
else
{
//父进程执行
j=kill(i,18); /*向子进程发送信号18*/
printf("Parent: signal 18 has been sent to child %d,returned %d.\n",i,j);
k=wait(&status); //等待子进程结束
printf("After wait %d,Parent %d: finished.\n",k,getpid());
exit(0);
}
}

void func(int signo) /*处理程序*/
{
printf("I am Process %d: It is signal 18 processing function.\n",getpid());
return;
}

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