c - fgets 和处理 CTRL+D 输入

Question

我正在从用户那里获取一些标准输入，如果用户按下 CTRL+D，我想显示错误并终止程序。我想我的问题可能与陷入 while 循环有关；

int readInput(){
   char buff[10];
   int count = 0;
   int counter;
   printf("Enter random number: ");
   fgets(buff, 10, stdin);
   if ((int) strtol(buff, NULL, 10) == 0){
      printf("Error reading number. \n");
      return 0;   //This will get hit if the user presses CTRL+D at this input.
   }
   counter = atol(buff);
   while (count < counter){ 
      printf("Enter a label: ");
      fgets(buff, 10, stdin);
      if ((int) strtol(buff, NULL, 10) == 0){
         printf("Error reading label");
         return 0;  //This will not get hit if the user presses CTRL+D at this input, but why?
         //I've also tried assigning a variable to 0, breaking out of the loop using break; and returning the variable at the end of the function but that also does not work.

      //the rest of the while loop continues even if user hit CTRL+D
      printf("Enter Value: " );
      fgets(buff, 10, stdin);
      //..rest of while loop just gets other inputs like above
      count++;
   }

//termination happens in main, if readInput returns a 0 we call RETURN EXIT_FAILURE;

我不明白为什么在第一次输入时，如果用户按下 CTRL+D，程序会做出相应的响应，但第二次它会完全忽略它。

Answer 1

在Linux上，Ctrl + D会产生EOF，所以每次都需要检查fgets()的返回值。当遇到EOF时，fgets()返回一个空指针

if (fgets(buff, 10, stdin) == NULL)
    print_error();