Fclose a file that is already fclose
c, c++, fclose
Solution
Calling `fclose` twice with the same stream is undefined behaviour - most likely crash. There is no way to check if `FILE*` has been closed already, so the safe solution is to set pointer to NULL as soon as it is closed:
fclose(fh);
fh = NULL;
Sources: "The value of a pointer to a FILE object is indeterminate after the associated file is closed" (C draft standard). "After the call to fclose(), any use of stream causes undefined behaviour." (The Single UNIX ® Specification).
Problem
In my programm I may close a file that is already close. What happen when I do a `fclose` on a file already close ? And if you can't do so, how to know if a file is closed or open ?