c - fork 后将父进程保持在前台

Question

我有一个 C 程序，它派生了一个子进程，我从 linux shell 运行它。

我的问题是，在 fork 之后，父进程移动到 shell 后台。我希望父进程留在前台。

这是一个简单的例子:

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

int main(void)
{
    int i;
    for (i = 0; i < 3; i++) {
        printf("Before Fork\n");
        sleep(1);
    }

    printf("forking...\n");
    pid_t pid = fork();
    if (pid) {
        // child
        printf("Child started and now exiting\n");
        exit(EXIT_SUCCESS);
    }

    // parent
    wait(NULL);
    for (i = 0; i < 3; i++) {
        printf("After Fork\n");
        sleep(1);
    }

    return 0;
}

输出(稍后添加注释)

Before Fork
Before Fork
Before Fork
forking...
Child started and now exiting
After Fork
gregp@gregp-ubuntu:~/fork_example$ After Fork       # <--- User returned to shell
After Fork

请注意，fork 后不久，用户将返回到 shell 提示符，程序继续在后台运行。我不希望这种情况发生。我希望程序继续在前台运行。

期望的输出(稍后添加评论)

Before Fork
Before Fork
Before Fork
forking...
Child started and now exiting
After Fork
After Fork
After Fork
                 # Program now exits and user returns to shell
gregp@gregp-ubuntu:~/fork_example$

Answer 1

第一个 pid 在父级中返回，所以你的条件应该是

if (!pid)

因为你代码中的child不会去if。那是因为

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.