Question

我的任务是编写一个C程序（“procs.c”），它创建了三个进程：一个创建两个子进程的父进程。

第一个孩子应该做到以下几点：

显示“第一个孩子出生，我的pid是......”
显示十次“第一个孩子执行迭代X”的消息，其中X是迭代次数
显示“第一个孩子安静地死去。”

第二个孩子应该做到以下几点：

显示“第二个孩子出生，我的pid是......”
显示十次“第二个孩子执行迭代X”的消息，其中X是迭代次数
显示“第二个孩子安静地死去。”

父进程应执行以下操作：

显示“父进程诞生，我的pid是......”
创建第一个孩子
创建第二个孩子
显示“父进程悄然死亡。”

使用gcc编译程序并命名可执行文件“procs”。多次执行程序并注意两个孩子的输出如何交错。属于项目这一部分的所有文件都应放在nova主目录中，并在H3分配下发布在Webtycho中。

该程序的可能输出是：

nova> ./procs

Parent process is born, my pid is 7847
First child is born, my pid is 7848    
First child executes iteration: 1
First child executes iteration: 2
First child executes iteration: 3
First child executes iteration: 4
First child executes iteration: 5
Second child is born, my pid is 7849
Second child executes iteration 1
Second child executes iteration 2
Second child executes iteration 3
First child executes iteration: 6
Second child executes iteration 4
Second child executes iteration 5
Second child executes iteration 6
First child executes iteration: 7
Second child executes iteration 7
Second child executes iteration 8
Second child executes iteration 9
Second child executes iteration 10
Second child dies quietly.
First child executes iteration: 8
First child executes iteration: 9
First child executes iteration: 10
First child dies quietly.    
Parent process dies quietly.

但是我得到的当前输出是：

nova2> ./procs
Parent process is born, my pid is: 1977
First child is born, my pid is: 1978
First child executes iteration: 1
First child executes iteration: 2
First child executes iteration: 3
First child executes iteration: 4
First child executes iteration: 5
First child executes iteration: 6
First child executes iteration: 7
First child executes iteration: 8
First child executes iteration: 9
First child dies quietly
Second child is born, my pid is: 1979
Second child executes iteration: 1
Second child executes iteration: 2
Second child executes iteration: 3
Second child executes iteration: 4
Second child executes iteration: 5
Second child executes iteration: 6
Second child executes iteration: 7
Second child executes iteration: 8
Second child executes iteration: 9
Second child dies quietly
Bus Error (core dumped)

我现在的代码是：

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

int main() {
    int pid, i;

    printf("Parent process is born, my pid is: %d\n", getpid());

    pid = fork();
    switch(pid) {
    case -1:
        /* an error occurred */
        printf("Fork error");
        break;

    case 0:
        /* this code is executed by child process #1*/
        printf("First child is born, my pid is: %d\n", getpid());

        for(i=1; i<10; i++)
            printf("First child executes iteration: %d\n", i);

        printf("First child dies quietly\n");

        exit(0);

    default: /* this code is executed by the parent process */

        if(fork()==0) {
            printf("Second child is born, my pid is: %d\n", getpid());

            for(i=1; i<10; i++)
                printf("Second child executes iteration: %d\n", i);

            printf("Second child dies quietly\n");
            exit(0);
        }

        wait();

        printf("Parent process dies quietly.\n");

    }
}

任何人都可以帮助我，我不确定是什么问题，因为我继续编码，对我来说似乎是对的。

Answer 1

wait函数接受一个参数，一个指向int的指针。省略参数意味着可以传递一些随机值，这意味着wait将尝试将子进程的退出状态写入某个随机内存位置，从而导致程序崩溃。一个简单的解决方法是传递NULL：

wait(NULL);

如果您编译了启用了警告的程序，编译器应该警告您。例如，gcc会告诉您：

test.c: In function ‘main’:
test.c:40:9: warning: implicit declaration of function ‘wait’ [-Wimplicit-function-declaration]
test.c:45:1: warning: control reaches end of non-void function [-Wreturn-type]

进程未正确运行

1 个答案: