stdin - 标准输入和输入缓冲区的内部工作

Question

我试图在 5 秒内打印用户输入的字符数。但是我在获取输入缓冲区时遇到了一些问题。

代码片段

---

# include <signal.h>
# include <sys/time.h>
# define INTERVAL 3
# define MAX_SIZE 1024

char buffer[MAX_SIZE];
int count = 0;

void alarm_handler (int i)
{
    printf("\r\n");
    printf("\nTimer expired.....\r\n");
    count = read(stdin,buffer,sizeof(buffer));
    puts(buffer);
    printf("count:%d\r\n",strlen(buffer));
    exit(0);
}

int main()
{
    signal(SIGALRM,alarm_handler); 
    alarm(INTERVAL);
    setbuf(stdin, NULL);

    printf("Start Triggering....\r\n");
    while (1)
    {
        gets(buffer);
    }
    return;
}

在上面的代码中，我没有得到用户输入的输入，并且输出缓冲区始终为零。谁能告诉我出了什么问题以及解决方案？

输出

++++++

开始触发....

阿卡卡卡卡卡

定时器超时......

计数：0

但我期待以下输出

++++++++++++++++++++++++++++++++++

开始触发....

阿卡卡卡卡卡

定时器超时......

阿卡卡卡卡卡

计数：14

请提出您对此的看法。

Answer 1

缓冲和类似的事情非常复杂。我对您的问题采取了稍微不同的方法 - 设置终端，以便立即将击键传递给程序（而不是等到<enter>被按下），并在发生时计算按下的键数。这需要使用getch()修改终端设置的功能。请注意，我确保终端在最后返回到其“旧”设置，以防中断“在错误的时间”发生。

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <sys/time.h>
#include <unistd.h>
#include <termios.h>
#define INTERVAL 3

int count = 0;
int flag = 0;
struct termios oldt; // keep old terminal settings to restore at the end

// function prototype - compiler was complaining. Not sure why?
unsigned int alarm(unsigned int interval);

void alarm_handler(int i) {
  flag = 1;
}

int getch(void)
{
  // function to return keystroke "as it happens"
  int ch;
  struct termios newt;
  tcgetattr(STDIN_FILENO, &oldt); /*store old settings */
  newt = oldt; /* copy old settings to new settings */
  newt.c_lflag &= ~(ICANON | ECHO); /* make one change to old settings in new settings */
  tcsetattr(STDIN_FILENO, TCSANOW, &newt); /*apply the new settings immediatly */
  ch = getchar(); /* standard getchar call */
  tcsetattr(STDIN_FILENO, TCSANOW, &oldt); /*reapply the old settings */
  return ch; /*return received char */
}

int main() {
  signal(SIGALRM,alarm_handler); 
  alarm(INTERVAL);

  printf("Start Triggering....\r\n");
  char c;
  do
    {
      c = getch(); // get key as soon as it's pressed
      putchar(c);  // and echo to the screen
      count++;     // increment counter
    } while (!flag);

  printf("\nTimed out!\nCharacter count = %d\n", count);
  tcsetattr(STDIN_FILENO, TCSANOW, &oldt); /*reapply the old settings */

  return 0;
}