1，2，3，4》。
以下这个小程序展示如何生成一个进程，执行任务，并且当任务完成后捕捉到子进程的信息。]]>
/* One process program */
/* This sample shows how to use fork(),execlp() and waitpid() */
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
main()
{
pid_t pc, pr;
pc=fork();
if(pc<0)
printf("Error occured on forking.\n");
else if(pc==0){ /* open /etc/hosts with nedit */
execlp("nedit", "nedit","/etc/hosts", NULL);
exit(0);
}
do{
pr=waitpid(pc, NULL, WNOHANG);
if(pr==0){
printf("No child exited\n");
sleep(1);
}
}while(pr==0);
if(pr==pc)
printf("successfully get child %d\n", pr);
else
printf("some error occured\n");
}
对于多个进程的情况，还需要学习关于信号的知识。因为进程一旦调用了wait，就立即阻塞自己。而采用信号处理程序（signal handler）就能够避开这个缺点。关于信号处理可以参考《Introduction To Unix Signals Programming》，关于多进程编程可以参考《Unix Multi-Process Programming and Inter-Process Communications (IPC)》。
下面这个程序展示了如何产生两个进程，在二十秒之内有进程退出后就提交指定任务。/* multi process program */
/* This sample shows how to fork two procss */
/* and submit new task once there is task finished */
/* in a period of time */
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <signal.h>
void catch_child(int sig_num)
{
int child_status;
pid_t pc, pr;
pr=wait(&child_status);
printf("child %d exited.\n",pr);
pc=fork();
if(pc<0)
printf("Error occured on forking.\n");
else if(pc==0){ /* open /etc/hosts with nedit */
execlp("nedit", "nedit","/etc/hosts", NULL);
exit(0);
}
}
main()
{
signal(SIGCHLD, catch_child);
int child_pid[2];
int i,j;
for(j=0;j<2;j++){ /* generates two child-process */
child_pid[j] = fork();
switch (child_pid[j]) {
case -1:
perror("fork");
exit(1);
case 0:
printf("hello world\n");
sleep(5); /* sleep a little, so we'll have */
/* time to see what is going on */
exit(0);
default:
break;
}
}
for (j=0; j<20; j++) {
printf("%d\n", j);
sleep(1); /* sleep for a second, so we'll have time to see the mix */
}
}
]]>