(gdb) backtrace
#0  0x00007ffff7a93baf in _int_free (av=0x7ffff7dd3760 <main_arena>, p=<optimized out>, have_lock=0)
    at malloc.c:3996
#1  0x00007ffff7a82565 in _IO_new_fclose (fp=0x602010) at iofclose.c:85
#2  0x00000000004008f9 in main (argc=2, argv=0x7fffffffde30) at main.c:113