c

Question

我正在写一个C程序。所有代码都在while循环中，但我还没有添加它。它需要来自用户的输入，例如start ls -l并运行ls -l。等待新命令。如果用户写“等待”并且有一个未结束的进程，它将等待子进程完成并打印刚刚完成的子进程ID并接受新命令。我的等待命令不起作用，我需要你的帮助。

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


int main (int argc, char **argv) 
{   

    char command[1024];
    char *cmd;
    char *ptr1;
    char *ptr2 = (char*)malloc(10 * sizeof(char));
    char *ptr3;
    char *pos;
    char *args[3];
    char tmp[1024];
    int count = 0;
    int cstatus;
    pid_t  child;
    pid_t c;


    printf("newShell> ");
    fgets( command, 1024, stdin );


    if ((pos=strchr(command, '\n')) != NULL)
            *pos = '\0';

    if (strlen(command) > 1024)
    {
        printf("Command is too long\n");
        exit(1);    
    }

    strcpy(tmp,command);

    ptr1 = strtok(tmp," ");
    cmd = ptr1;


    while(ptr1 != NULL) 
    {   
        ptr1 = strtok(NULL, " ");


        if (ptr1 == NULL) break;

        if (count == 0)
        {
            ptr3 = ptr1;

            count = 1;
        }

        else
            strcat(strcat(ptr2,ptr1)," ");
        }

    ptr2[strlen(ptr2) - 1] = '\0';

    args[0] = ptr3;
    args[1] = ptr2;
    args[2] = NULL;

    if (strcmp(cmd,"start") == 0)
    {
        if ((child = fork()) == 0) 
        { 
            printf("\nProcess %ld is started\n", (long) getpid());
            execvp(args[0], args); 

            fprintf(stderr, "execvp() couldn't do the process\n");
            exit(1);
        }

        if (child == (pid_t)(-1)) 
        {
            fprintf(stderr, "Fork error.\n"); exit(1);
        }
    }

    else if (strcmp(cmd,"wait") == 0)
    {   

        if (child > 0)
        {
            c = wait(&cstatus); 
            printf("Process %ld completed with code: %d \n",
            (long) c, cstatus);
        }
        else
            printf("There is no process\n");
    }   


}

编辑：

我应该用以下内容更改该部分：

child = fork();

    if (child == (pid_t)(-1)) 
    {
            fprintf(stderr, "Fork failed.\n"); 
            exit(1);
    }

    if (strcmp(cmd,"start") == 0)
    {
        if (child == 0) 
        { 
            printf("\nProcess %ld is started\n", (long) getpid());
            execvp(args[0], args); 

            fprintf(stderr, "execvp() couldn't do the process\n");
            exit(1);

            continue;
        }

    else if (strcmp(cmd,"wait") == 0)

        c = wait(&cstatus); 
        printf("Parent: Child  %ld exited with status = %d\n",
        (long) c, cstatus);
        continue;


    }

Answer 1

进程只能等待自己的子进程。您需要将while循环添加到您的程序中，以便它可以等待它分叉的子节点。您无法重新运行该程序并等待上一次调用启动的进程，因为该进程不是它的子进程。

所以你需要在你的程序中添加while循环。

while (1) {
    printf("newShell> ");
    fgets( command, 1024, stdin );

    ... // all the rest of your code
}

请注意，您可能无法找到newShell>提示。由于您的程序在返回循环开始之前不会等待子进程，因此它通常会在子进程运行之前打印提示并打印其输出。