Why do stdio functions (fgetc, fgets, getc, getchar) always return EOF in RHEL 8 and later?

Issue

• Different return value of fgetc(3) and sibling functions, since RHEL 8

• The following code (test1.c) works on RHEL 7 but not on RHEL 8 and later

  #include <stdio.h>
  
  int main(int argc, char *argv[])
  {
      char buffer[1024];
      char *str;
      FILE *fptr_w = fopen("data", "w");
      FILE *fptr_r = fopen("data", "r");
  
      fprintf(fptr_w, "%s", "Hello, world!");
  
      str = fgets(buffer, 1024, fptr_r);
      printf("s = %s\n", str);
  
      fflush(fptr_w);
  
      str = fgets(buffer, 1024, fptr_r);
      printf("s = %s\n", str);
  
      return 0;
  }
  

• Result on RHEL 7:

  $ cc -o test1 test1.c
  $ ./test1
  s = (null)
  s = Hello, world!
  

• Result on RHEL 8:

  $ cc -o tes1t test1.c
  $ ./test1
  s = (null)
  s = (null)