Linux编程：进程间通信--管道

编程内容：
1.父进程创建管道和两个子进程p1和p2
2.子进程p1打开给定文件（如果没有，则创建文件），并向文件中写数据，写完关闭文件，然后向管道写入一条消息“ok”，目的是通知进程p2可以读取文件内容了。
3.子进程p2通过管道读取消息，如果消息是“ok”,则打开文件，读取文件内容，并将其输出到屏幕上,关闭文件。

/*
create by : Koala
...
*/
#include <stdio.h>
#include <unistd.h>
#include <string.h>

int main()
{
    int filedes[2]; //Declare read or write parameter
    char buf[100]; //Declare buffer segment for pipe
    char buff[100]; //Declare buffer for file
    pid_t fpid,pid1,pid2; //Declare father process and two children processes
    fpid = getpid();
    pipe(filedes); //Create a pipe
    printf("The father process's PID is: %d\n",fpid);
    char dir[100];//Declare file direction
    if((pid1 = fork()) == 0)
    {
        printf("Children process1's PID is: %d and its father process's PID is: %d\n",getpid(),getppid());
        FILE *fp;
        printf("Please enter the file direction:\n");
        fgets(dir,sizeof(dir)-1,stdin);
        fp = fopen(dir,"w+");//Open file"hello pipe.txt",if failed then create
        if(fp == NULL)
        {
            printf("The file cannot be open or create!\n");
        }
        else
        {
            //Write data to file
            fwrite ("hello pipe!", 1,sizeof("hello pipe!")-1,fp );
            fclose(fp);
            fflush(fp);

            char s[] = "OK";
            write(filedes[1], s, sizeof(s));
            close(filedes[0]);
            close(filedes[1]);
        }
    }
    if((pid2 = fork()) == 0)
    {
        printf("Children process2's PID is: %d and its father process's PID is: %d\n",getpid(),getppid());
        read(filedes[0],buf,sizeof(buf));
        if(strcmp(buf,"OK"))
        {
            FILE *fpr;
            fpr = fopen(dir,"r");
            if(fpr == NULL)
            {
                printf("The file does not exist!\n");
            }
            else
            {
                while(fgets(buff,1024 ,fpr)!= NULL)
                {
                    fprintf(stderr,"%s",buff);
                }

                getchar();
                printf("\n");
                fclose(fpr);
            }
            close(filedes[0]);
            close(filedes[1]);
        }
    }
    pid_t childpid =wait(NULL);
    printf("Process of %d exited\n",childpid);
    return 0;
}

运行结果截图：