关于系统调用的问题，如fork()和C中的pipe()。-QuestionsaboutSystmcallslikefork()andpipe()inC

   #include
   #include
   #include
   #include
   #include

   int main(int argc, char **argv){
       int n = atoi(argv[1]);
       int superdaddy = getpid();
       int p[n+1][2];
       int i=0;
       int cpid,output;
       int result = 0;

       if(pipe(p[0])<0){
           perror("1");
           return 1;
       }
       if(pipe(p[n])<0){
           perror("2");
           return 1;
       }
       output = p[0][1];
       if(getpid()==superdaddy){
           if(write(p[0][1],&result,sizeof(result))<0){
               perror("3");
               return 1;
           }
           if(close(p[0][1])<0){
               perror("4");
               return 1;
           }
       }
       while(1){
           if(i==n){
               if(read(p[n-1][0],&result,sizeof(result)<0)){
                   perror("5");
                   return 1;
               }
               result++;
               output = p[n][1];
               if(write(output,&result,sizeof(result))<0){
                   perror("6");
                   return 1;
               }
               if(close(p[n-1][0])<0){
                   perror("7");
                   return 1;
               }
               if(close(p[n][1])<0){
                   perror("8");      
                   return 1;
               }
               break;
           }
           i++;
           cpid = fork();
           if(cpid==0){
               if(i==n)
                   continue;
               if(pipe(p[i])<0){
                   perror("9");
                   return 1;
               }
               if(read(p[i-1][0],&result,sizeof(result))<0){
                   perror("10");
                   return 1;
               }
               result++;
               output = p[i][1];
               if(write(output,&result,sizeof(result))<0){
                   perror("11");
                   return 1;
               }
               if(close(p[i-1][0])<0){
                   perror("12");
                   return 1;
               }

               if(close(p[i][1]<0)){
                   perror("13");
                   return 1;
               }
               continue;
           }
           else if(cpid<0){
               perror("14");
               return 1;
           }
           break;
       }

       if(getpid()==superdaddy){
           wait(NULL);
           if(read(p[n][0],&result,sizeof(result))<0){
               perror("15");
               return 1;
           }
           printf("Result: %d\n",result);
           if(close(p[n][0])<0){
               perror("16");
               return 1;
           }
       }
       return 0;
   }

The Program aims to read a number n from command line and then forks n child process and create n pipes. process p0 will be parent of process p1, p1 will be parent of p2, so and so on. One variable (named result here) will be passed through pipes, every time it is passed it will be added by 1. So the output should be n as well. Pipe Fi connects Pi and P(i+1). Attached is my code.

该程序旨在从命令行读取数字n，然后派生n个子进程并创建n个管道。进程p0是进程p1的父进程，p1是进程p2的父进程，以此类推。一个变量(此处命名为result)将在管道中传递，每次传递时它将被1添加。所以输出也应该是n。管道Fi连接Pi和P(i+1)。附件是我的代码。

When n=1 or n=2, the program can output correctly, which is 1 and 2 correspondingly. However, when n=3, it gives me a bad file error at error 5. I have hand-tracked the code for the whole afternoon but got no idea what is wrong with it. Anyone could help? Appreciate it first!

当n=1或n=2时，程序可以正确输出，即1和2。然而，当n=3时，它在错误5处给出了一个错误的文件错误。整个下午我都在跟踪代码，但不知道它有什么问题。任何人都可以帮忙吗?先欣赏它!

1 个解决方案

if (i == n) {
    if(read(p[n-1][0],&result,sizeof(result)<0)){
        ...
    }
}

#include 
#include 
#include 
#include 
#include 

int
main(int argc, char *argv[])
{
    if (argc != 2) {
        fprintf(stderr, "Usage: %s N\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    int n = atoi(argv[1]);
    int pipes[n][2];
    int i, val;
    pid_t pid;

    val = 0;

    for (i = 0; i 

$ ./a.out 3
P 2005 writes 0
C 2006 read 0
P 2006 writes 1
C 2007 read 1
P 2007 writes 2
C 2008 read 2
2008 is going to leave.
2007 is going to leave.
2006 is going to leave.
2005 is going to leave.