如何在 fgets 循环中正确刷新 stdin [英] How to properly flush stdin in fgets loop

问题描述

我在此处多次找到使用 while((c = getchar()) != '\n' && c != EOF) 清除 stdin 的示例，并且试图在通过 fgets 获取输入的循环中使用它.我需要刷新，因为循环从最后一个输入中获取 \n 字符并再次运行.

I have found the example of clearing stdin using while((c = getchar()) != '\n' && c != EOF) on here a few times, and tried to use it in a loop that gets input via fgets. I need to flush, since the loop takes the \n character from the last input and runs with it again.

所以现在我必须按两次回车键.为什么会发生这种情况，我该如何解决?

So what happens is that I have to press enter twice now. Why is this happening, and how can I fix this?

#define BUFFER_LIMIT 50
do
{
  int c;
  while ((c = getchar()) != '\n' && c != EOF);

  printf("console> ");
  fgets(input_buffer, BUFFER_LIMIT-1, stdin);

  if(do_something(input_buffer))
    break;
} while(strncmp(input_buffer, "quit", 4) != 0);

推荐答案

所以现在我必须按两次回车键.为什么会发生这种情况，我该如何解决?

So what happens is that I have to press enter twice now. Why is this happening, and how can I fix this?

好吧，这就是您的代码所做的 - 它首先逐个字符读取，直到找到换行符.然后它调用 fgets() 这将......好吧，阅读直到它找到一个换行符(可能是逐个字符，但也可能以其他方式).

Well, that is what your code is doing - it first reads char-by-char until it finds newline. Then it calls fgets() which will... well, read until it finds a newline (probably char-by-char, but, also possibly in some other way).

您可以尝试 fflush(stdin)，但这并不能保证做您想要的(它只保证输出缓冲区，不保证输入).

You could try fflush(stdin), but that is not guaranteed to do what you want (it only gives guarantees for output buffers, not for input).

此外，您可以尝试 setbuf(stdin, NULL) ，它应该禁用标准输入的缓冲，因此没有任何东西可以刷新.我在不同的系统上尝试了几次，它奏效了，但此功能的文档对此并不是 100% 清楚.

Also, you may try setbuf(stdin, NULL) which should disable buffering on standard input, so there would be nothing to flush. I tried this a few times on different systems and it worked, but documentation for this function is not 100% clear on this.

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