yyin & fopen.

Author: janpgit

docs/class-assignments/labs-assignment-2020.txt

@@ -90,6 +90,9 @@ Family of fopen(), fread() functions, et al are prohibited.  Instead use
 functions from the printf(3) family, and system calls like open(2),
 read(2), write(2), etc.
 
+!!!! The only exception is the use of fopen() to initialize flex's yyin
+for a non-interactive shell mode - that is allowed.
+
 popen(3), system(3), and all other functions that fork() inside are
 strictly prohibited.  The only way to create a new process for you is to
 use fork(2).