使用 fork() 创建进程树然后给它们编号并在数组上显示

你的主要问题是你的孩子会继续他们父母的循环并创造更多你认为的孩子。我只能建议你读两次的曼努埃尔的fork()。管理流程创建并不容易。您需要了解您的孩子会复制 (~) 其父母的所有状态。两者都将执行相同的代码，因此您需要注意在您的 fork 之后将执行哪些代码取决于fork().

EOF的评论是为了建议您不要fork()在函数中使用更多。您会看到我的实现示例通过没有两个fork()调用来保持简单，我将调用隔离在一个特定的地方。

这是您的第一个代码的正确实现：

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

static int create_two_child(int i, int n);

int main(void) { return create_two_child(0, 2); }

// tail recursive function: child will call this function to create two new
// child
static int create_two_child(int i, int n) {
  if (i < n) { // we look our level
    // debug output
    printf("DEBUG: We are in the level %d and as a child PID:%d, PPID:%d\n", i,
           getpid(), getppid());
    fflush(stdout); // we don't want child print parent output
    for (int j = 0; j < 2; j++) { // we loop to create two child
      pid_t pid = fork();
      if (pid == -1) { // error
        perror("fork()");
        return 1;
      } else if (pid == 0) {               // child
        return create_two_child(i + 1, n); // we call ourself with i + 1 and
                                           // stop function here wich return we
                                           // don't want that child continue the
                                           // loop
      }
      // parent will continue the loop to the number of child wanted
    }
  } else {
    // if we are at max level we show our pid
    printf("We are in the level max %d and as a child PID:%d, PPID:%d\n", i,
           getpid(), getppid());
  }
  return 0;
}

您想要显示树的第二个实现：

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

static int create_two_child(size_t *backtrace, size_t id, size_t i, size_t n);

int main(void) {
  // we create array to stock id
  size_t backtrace[3];
  size_t n = sizeof backtrace / sizeof *backtrace;
  return create_two_child(backtrace, 1, 0, n);
}

// tail recursive function: child will call this function to create two new
// child
static int create_two_child(size_t *backtrace, size_t id, size_t i, size_t n) {
  if (i < n) {                       // we look our level
    for (size_t j = 0; j < 2; j++) { // we loop to create two child
      pid_t pid = fork();
      if (pid == -1) { // error
        perror("fork()");
        return 1;
      } else if (pid == 0) { // child
        backtrace[i] = id + 1;
        // id * 2 cause we create 2 child each time
        return create_two_child(backtrace, id * 2, i + 1,
                                n); // we call ourself with i + 1 and
                                    // stop function here wich return we
                                    // don't want that child continue the
                                    // loop
      }
      id++;
      // parent will continue the loop to the number of child wanted
    }
  } else {
    // if we are at max level we show our backtrace
    printf("Last Level Children: 1");
    for (size_t j = 0; j < n; j++) {
      printf(", %zu", backtrace[j]);
    }
    printf("\n");
  }
  return 0;
}