Linux||Linux操作之Shell教程--使用fork创建进程、使用exec替换子进程程序、分析进程的父进程、共享存储区进程通信机制、消息队列实现进程通信（Ubuntu 16.04）

#include<unistd.h>
#include<string.h>
#include<stdlib.h>
#include<stdio.h>
int main()
{

    int i=0,X=0;
    pid_t p1,p2;
    p1 = fork();//鍒涘缓涓€涓柊process
    if(p1 < 0)
    {
            printf("fork() error");
            exit(1);
    }
    else if(p1 == 0)
    {
                for(int i = 0;i<4;i++)
                {
                        printf("The PID of child1 = %d, X = %d\n",getpid(),X);
                        X =X + 2;
                }
    }
    else
    {
        p2 = fork();//鍒涘缓绗簩涓柊杩涚▼
        if(p2 < 0)
        {
            printf("fork() error");
            exit(1);
        }
        else if(p2 == 0)
        {
                        for(int i = 0;i<4;i++)
                        {
                                printf("The PID of child2 = %d, X = %d\n",getpid(),X);
                                X = X + 2;
                        }
        }
        else
                {
                        for(int i = 0;i<4;i++)
                        {
                                printf("The PID of Parent = 2021308310230 鏉庡▍濠? X=%d\n",X);
                                X = X +2;
                        }
        }
    }
    getchar();//涓轰簡鎷︿綇杩涚▼锛屼笉璁╄繘绋嬬粨鏉?
    return 0;
}

#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>

int main()
{
	int i;
	int p, ppid;
	printf("begin\n");
	p = fork();
	if (p == -1)
	{
		printf("fork() error");
		exit(-1);
	}
	if (p == 0) //child process
	{ 
	    for (i=0; i<10; i++)
		{
			ppid=getppid();
			printf("This is child. The PID of Parent is %d\n", ppid);
			sleep(2);
		}
	}
	else
	{
		sleep(3);
		printf("This is parent. The parent process will stop running\n");
	}
	printf("The end\n");
	return 0;
}

#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/types.h> 
#include <sys/msg.h> 
#include <sys/wait.h>
#include <unistd.h>
#include <stdlib.h>
#define KEY 100
#define SIZE 10
struct msgform{
	long mtype;
	char mtext[100];
}msg,smsg;
int main()
{
	int num[SIZE];
	int shmid,i;
	char *shmaddr;
	int sum=0;
	int *p;
	int x;
	int msgid;
	//use shm to deliver data
	shmid=shmget(KEY,sizeof(int)*SIZE,0777|IPC_CREAT);
	if(shmid==-1){
		printf("shmget error!\n");return 0;
	}
	shmaddr=shmat(shmid,NULL,0);
	p=(int *)shmaddr;
	//input data
	for(i=0;i<SIZE;i++){
		printf("杈撳叆绗?%d涓暟瀛?",i+1);
		scanf("%d",p++);
	}
	p=p-5;
	//compute sum of the five numbers
	for(i=0;i<SIZE;i++){
		sum+=*p++;
	}
	printf("SUM:%d\n",sum);
	//use msg queue to deliver result
	msgid=msgget(KEY+1,0777|IPC_CREAT);
	if(msgid==-1){
		printf("msgget error!");return 0;
	}
	if((x=fork())==-1){
		printf("fork error!\n");return 0;
	}
	if(x==0){// child process
		int sum_power2=0;
		p=p-5;
		for(i=0;i<SIZE;i++){
			int temp=*p++;
			sum_power2=sum_power2+temp*temp;
		}
		//send data
		smsg.mtype=1;
		sprintf(smsg.mtext,"%d",sum_power2);
		if(msgsnd(msgid,&smsg,100,0)==-1){
			printf("msgsnd error!\n");return 0;
		}
		return 0;
	}else{//parent process
		wait(NULL);
		//receive data
		msgrcv(msgid,&msg,100,1,0);
		printf("square sum:%s\n",msg.mtext);
	}
	//release resources
	msgctl(msgid,IPC_RMID,0);
	shmdt(shmaddr);shmctl(shmid,IPC_RMID,0);return 0;
}

#include <sys/types.h>
#include <stdio.h>
int main()
{  int i;
     pid_t pid,ppid;
     printf("begin\n");
     pid = fork();
     if(pid == -1)
     {    printf("fork error");
          exit(-1);
     }
       if   (pid == 0) //child process
           { for (i=0; i<5; i++)
            {  ppid=getppid(); 
               printf("parent Pid:%d\n", ppid);
               sleep(2);
             }
            }
       else
       {   sleep(3);
           printf("The parent process will stop running\n");
        }
       printf("end");
     }