c++ - 消失的子进程

Question

我有这个方法:

int build_pipe_and_call(char **argv1, std::string cmd1, char **argv2, std::string cmd2, int conc) {
    std::cout << "Building Pipe...\ncmd1: " << cmd1 << "\n cmd2: " << cmd2 << "\n";
    int *pipefd = new int[2];
    if (pipe(pipefd) < 0) {
        std::cerr << "There was an error setting up the pipe.\n";
        return -1;
    }
    pid_t cpid1 = fork();
    std::cout << "First process forked, cpid: " << cpid1 << " - Process " << getpid() << "\n";
    switch (cpid1) {
        case -1:
            std::cerr << "There was an error forking the process.\n";
            return -1;
            break;
        case 0: // this is the part that isn't executing
            std::cout << "Dup2 return: " << dup2(pipefd[1], 1) << "\n";
            std::cout << "Process " << getpid() << " duped and about to exec.\n";
            execvp(cmd1.c_str(), argv1);
            std::cout << "Process " << getpid() << " about to exit.\n";
            _exit(0);
            break;
        default:
            pid_t cpid2 = fork();
            switch (cpid2) {
                case -1:
                    std::cerr << "There was an error forking the process.\n";
                    return -1;
                    break;
                case 0:
                    dup2(pipefd[0], 0);
                    std::cout << "Process " << getpid() << " duped and about to exec.\n";
                    execvp(cmd2.c_str(), argv2);
                    _exit(0);
                    break;
                default:
                    if (conc) {

                    } else {
                        int status1, status2;
                        std::cout << "Process " << getpid() << " about to wait.\n";
                        waitpid(cpid1, &status1, 0);
                        waitpid(cpid2, &status2, 0);
                    }
                    break;
            }
        }
    delete[] pipefd;
    return 0;
}

我添加打印语句只是为了调试。但是，当此方法运行时，这就是打印的内容。

Building Pipe...
cmd1: cat
cmd2: wc
First process forked, cpid: 1454 - Process 1453
First process forked, cpid: 0 - Process 1454
Process 1453 about to wait.
Process 1455 duped and about to exec.

进程 1454 是第一个派生的进程，它在创建后立即打印消息。但是，它从不打印来自 switch 语句的任何消息，也从不执行指定的程序(在本例中为 cat)。该进程不会像僵尸一样徘徊，它只是消失了。结果，第二个子进程挂了，实际上什么也没做。

(另外，补充一下，我知道我还没有添加所有适当的错误处理，功能还没有完成)。

Answer 1

您没有看到来自 switch 语句的消息，因为它们已被写入管道。尝试将 std::cout 替换为 std::cerr。