c - 使用 fork() 获取 child 的 child

Question

我在操作系统课上遇到了一些问题。我需要在 C 中编写一个函数，其中每个 child 生成另一个 child ，并且每个 parent 只能有一个 child 。我还必须打印他们的 pid。

这是我目前所拥有的:

#define MAX_COUNT 10

pid_t ex5_1 (pid_t pid) {
    pid = fork();
    if (!pid) {
        printf("ID %d Parent %d \n", getpid(), getppid());
        _exit(1);   
    }
    return pid;
}
void ex5 () {
     pid_t  pid;
     int    i;
     pid = fork();
     for (i = 1; i <= MAX_COUNT; i++) {
          pid = ex5_1(pid);
          int status;
          wait(&status);
     } 
}

如果有人能提供帮助，我将不胜感激!

Answer 1

这是这个人对 fork 的评价:

On success, the PID of the child process is returned in the parent, and 0 is returned in the child. On failure, -1 is returned in the parent, no child process is created, and errno is set appropriately.

所以你只需要像这样检查 fork 的返回:

int pid = fork();
if (pid < 0)
    // error handling here
else if (pid == 0)
    // here you are in the child
else
    // here you are in the parent

最后，要在 child 中创建一个 child，您可以这样做:

void child(int i)
{
    int pid;

    printf("Child number %d, ID %d Parent %d \n", i,  getpid(), getppid());
    if (i == MAX)
        return;
    pid = fork();
    if (pid < 0)
        // error handling here
    else if (pid == 0)
        child(++i);
    else
        waitpid(pid, null, 0);
    exit(0);
}

int main() {
    int i = 0;  
    int pid = fork();
    if (pid < 0)
        // error handling here
    else if (pid == 0)
        child(++i);
    else
        waitpid(pid, null, 0);
}