C：循环不使用循环语句或递归 [英] C: Looping without using looping statements or recursion

问题描述

我想写一个C函数将在标准输出，其中N是一个int型参数的函数打印1到N一种全每一行。该功能不能使用，同时，对，做-whil​​e循环，goto语句，递归和switch语句。是否可以？我想找到一个答案，因为这是一个挑战问题

I want to write a C function that will print 1 to N one per each line on the stdout where N is a int parameter to the function. The function should not use while, for, do-while loops, goto statement, recursion, and switch statement. Is it possible? I want to find an answer to this as this a challenge question

推荐答案

通过阻塞读，信号和报警。我想我必须使用的sigaction和SA_RESTART，但它似乎工作不够好，没有。

With blocking read, signals and alarm. I thought I'd have to use sigaction and SA_RESTART, but it seemed to work well enough without.

需要注意的是setitimer函数/报警可能是UNIX /般特有的。

Note that setitimer/alarm probably are unix/-like specific.

#include <signal.h>
#include <sys/time.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

volatile sig_atomic_t counter;
volatile sig_atomic_t stop;

void alarm_handler(int signal)
{
  printf("%d\n", counter++);
  if ( counter > stop )
  {
    exit(0);
  }
}

int main(int argc, char **argv)
{
  struct itimerval v;
  v.it_value.tv_sec = 0;
  v.it_value.tv_usec = 5000;
  v.it_interval.tv_sec = 0;
  v.it_interval.tv_usec = 5000;
  int pipefds[2];
  char b;

  stop = 10;
  counter = 1;

  pipe(pipefds);

  signal(SIGALRM, alarm_handler);

  setitimer(ITIMER_REAL, &v, NULL);

  read(pipefds[0], &b, 1);
}

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